Experience
in a Book
Engine
Modifications
The following is a collection of comments regarding
modifications for the XJ-S. Most are performance-related,
but a few are not. The owner who merely wishes to drive at
the speed limit nevertheless may still benefit from this
section; many of the suggested modifications (such as the
replacement of the steering rack mounts) are suggested for
everyone, and many suggestions are worth considering for
their ease of implementation.
AIR FILTER REPLACEMENT: K&N Engineering, Inc.,
makes permanent air filters consisting of special fabric
sandwiched between aluminum mesh and treated with oil. They
have much less flow restriction than stock paper filters,
while still providing excellent filtration. Tests on race
engines show only a slight drop in power compared to no
filters at all! Since these filters are permanent and
cleanable, they can even save money in the long run.
The part number is 33-2011 for any pre-1991 XJ-S. Note
that stock air filters changed when the ABS brakes were
added; since the housing shifted forward, the blank-off area
over the throat had to move rearward. The K&N filters
have no blank-off area, so the same part number fits either
application.
Roger Bywater of AJ6 Engineering says, "...we gave up
using K&N filters some time ago because they fall to
bits around the edges where the air box clamps up. We raised
the matter with K&N Europe, for whom we do consultancy
work on occasions, but they claim not to be aware of the
problem..." AJ6 Engineering now offers their own design
permanent washable foam air filters.
Glen E. MacDonald notes, "Roger Bywater gave up using
K&N filters because "they fall to bits around the edges
where the airbox clamps up". True enough. However, I was
determined not to trash an otherwise perfectly acceptable
(and expensive to replace) pair of filters. The fix I found
was to take four suitable lengths of windshield washer hose,
split lengthwise. These are then slid over the edges of the
filter, after cleaning off whats left of the 'bits' Bywater
refers to. I made this alteration over 3 years ago and
haven't had any problem since."
Of course, K&N filters come with a "million mile
warranty", so another option would be to gripe to K&N
about the problem.
For some of us, performance is not the issue with air
filters; the wear rate of an engine can be closely related
to the filtration of the air intake, and any risk of
inferior filtration would not be worthwhile. K&N claims
that a NASCAR stock car fitted with its filters will
outperform a car with no filters over a 500-mile event,
since the deterioration of the engine due to contaminated
air over 500 miles will exceed the power loss due to the
intake restriction of a K&N filter. K&N claims
excellent filtration -- although there have been some
contradictory reports from other sources. K&N filters
contain a layer of cotton soaked with sticky oil; as the air
passes through the cotton, particles should stick to the
oil. Such a system normally is not described as a particular
size micron filter, since it really should stop all
particles regardless of size. The stock paper filter, on the
other hand, is a porous media filter, and particles below a
certain size are free to pass right through.
Either K&N or the stock paper filter is probably
acceptable. However, speaking as an engineer, I must express
doubts about the filtration efficiency of most of the foam
filters I have seen (I haven't seen the AJ6 Engineering foam
filters). A foam filter works on a similar theory as the
K&N, the foam providing a media for the air to pass
through that is coated with sticky oil. However, the
passages between the cotton fibers on a K&N filter are
very tiny indeed, it's hard to imagine how a speck of dust
could get through without sticking, but some foam filters
you can see through. And even those you can't see
through appear to have passages that are quite large. And
I've also seen foam deteriorate, with crumbs of foam
breaking off and going into the inlet.
AIR INTAKE MODS - VERSION 1: Each of the air
cleaner housings has a long tapered tube with a relatively
small opening for the air intake. The purpose of the small
intake opening is to accelerate the air to near Mach 1 at
wide open throttle. This prevents intake sound from coming
forward through the intake. In other words, it makes the car
quiet.
Unfortunately, the air is now moving fast, and there's an
air filter up ahead. If the air is allowed to simply run
into the filter, the energy associated with the speed will
be wasted, and the result is a loss of pressure. Therefore,
Jaguar provides the tapered tube to gradually and
efficiently slow the air down, recovering most of the energy
and pressure. Jaguar designed this tapered tube as long as
they could fit under the hood.
Also unfortunately, once the air reaches Mach 1, the
passage is "choked" and all the sucking the engine can
manage will not increase the amount of air flowing through
it. The opening therefore forms an absolute control on the
maximum amount of air going into the engine -- and therefore
the HP generated.
If you cut off this intake tube and form a large opening
for the air intake into the air cleaner housing, you will
eliminate this restriction. If you interfere with the
mounting of the temperature sensor in the left side intake
tube, relocate it into the housing itself (drill a hole and
use a nut on the inside); it can sense the air temperature
anywhere in there. Because the EFI system detects manifold
vacuum, the system will automatically compensate for the
increased airflow; no tuning modifications are required.
There is no effect on emissions, so there should be no
complaints from inspectors.
At part throttle (most of the time with an engine this
powerful), the butterfly acts as an air-accelerating
restriction, and no sound gets out anyway. The car will
sound like it did before. However, when you open it up, you
will be greeted with a sonorous growl from under the hood.
This is a very sexy sound, but some Jag owners may not like
it.
The performance improvement goes along with the noise. In
any situation where there is still no sound, there is no
change in performance either. When the engine growls, there
is more airflow than there was before.
This mod will have no effect on fuel economy, except when
you hear the growl; at that point, increased fuel use
accompanies the increased airflow and increased power.
You can give this mod a trial run without much effort.
Unscrew the air temperature sensor, then reconnect the wire
to it and tape it down anywhere convenient. Then, remove
both air filter covers and tie the air filters in place with
some wire. This setup will provide the same performance (and
a little more noise) than the intake tube removal described
above.
AIR INTAKE MODS - VERSION 2: Any engineer will
tell you that an internal combustion engine will run more
efficiently (more power and better fuel economy) on
cooler intake air. Most automobiles nowadays (including some
Jaguars) have hoses directing cool outside air into the air
cleaners rather than the hot air of the engine compartment.
The XJ-S is a notable exception; perhaps they felt that the
hoses would make their engine compartment less
attractive.
While opening up the intakes on the air filter housings
as described above, a flange can be provided for an intake
hose. One such installation used 3" exhaust pipe, but 2‡"
pipe would work nearly as well (still four times the area of
the stock inlet) and would probably be easier to install.
Intake hoses in many sizes can be found at most parts
stores, and some have built-in clamps. Remember to provide
flexibility in the system, since the engine moves around on
its mounts.
All of that was easy. The hard part is routing the intake
hoses somewhere. The best place on the XJ-S appears to be
the back end of the headlight compartments. By making a hole
and providing a flange for the hose (2‡" or 3" pipe again),
cool air can be routed from existing openings just inside
the grille through the space behind the headlights and into
the intakes. An opening must be made in an unseen panel
within the headlight compartment to permit air flow. The
modification will also require relocating the headlight
relays. Be sure to clean up the intake path as well as
possible when you're finished, and check your air filters
for debris after driving a while.
On cars with ABS brakes, the air cleaner assemblies are
essentially unchanged except that they are moved forward to
avoid the brake system. It is uncertain what impact that
would have on the above modifications, if any.
The good news here is that this mod will reduce the noise
from the Version 1 mod. The intake hoses, as well as the
sheer length of the intake path, will help dampen the
growl.
Since the EFI temperature sensor will detect the cooler
intake air temperature, once again no tuning mods are
needed. The cooler air provides improvements at all
operating conditions, and will improve fuel economy. There
is even less tendency to overheat. The only effect on
emissions is a reduction in nitrogen oxide
emissions.
Peyton Gill reports, "I used a Dremel to cut the horn out
of the air filter cover and then rounded the "not so perfect
hole" with a grinding stone mounted in a drill press. I did
not use the exhaust pipe Kirby mentioned, I went to Home
Depot and got 2 inch gray PVC couplings. The ones I got came
from the electrical dept. The couplings I used have threads
on one side and open for a PVC pipe on the other. The
conduit works good because you can get a "nut" that fits the
threaded side. This nut I'm talking about is more like a
threaded ring, it is very common in the electrical conduit
world. The rounded hole you leave when you cut the horn out
is close to the same size as the threaded side of the
coupling and the nut inside the air filter holds the
coupling tightly in place. The hole I cut was not perfect so
I sealed any openings with black RTV (silicon). I did have
to relocate the ballast resistor pack on the right hand side
and managed not to have to relocate the relays on the left
hand side.
"I used a hole saw ( maybe 2 1/4 inch) or whatever size
slightly larger than the conduit coupling threads to cut
holes in the panels behind the headlights. Since the hole
was only slightly larger than the threads so they screw
fairly tightly in plus a little more RTV to be sure they
hold. I got a flexible hose from Pep Boys (they have hoses
made for air filter intakes). I took my conduit coupling
with me and found a hose that fit snugly over the pipe side.
The hoses have clamps that snap into place and one of the
hoses fit my conduit perfectly.
"All that was fairly easy; the good part comes when you
attack the "hidden panel" described in Kirby's book. This
panel is between the headlight opening in the front and
where the hole was cut in the engine compartment. You can
see it easily enough when the headlight assembly is removed.
Seeing the panel is one thing, cutting a hole in it's
another. There is not much room to work or cut. I got a 12
inch extension for my drill and put the hole saw on this and
cut a couple 2 inch holes in the panel.
"The air temp sensor also has to be relocated. I drilled
a hole in the air filter cover and placed the sensor in the
direct air path. I did not have a nut with the same size
threads as the sensor so I cut the fitting off the old horn
and used it as a nut. I don't think the threads are anything
special, I just did not want to make a trip to the hardware
store to get one. I had to extend the wires a little."
AIR INTAKE MODS - VERSION 2A: Scott Horner,
apparently before he became aware of this book, designed his
own cold air intake system: "I based the cold air intake on
my car on a friend's XJ-S race car's set-up. He has approx.
4" tubing going into the front of the inner guards, with the
air filters mounted within that panel (in front of the
wheels). But this is a bit rough for a road car as all you
can hear is induction roar...
"For my car, I visited a panel beater friend to modify
the guards, etc., as I wanted the mod to look as if it had
come out of the factory...
"I'll try and describe this without pictures...We used 2
1/2" tubing which is bent to come out of the inner guard and
face up to the original air intakes, which have been cut
down (with new tubing) to just a stub and attached via
flexible tubing.
"Within the guard, the tubing is bent down (to vertical)
which then meets up with another piece of tubing (via
flexible hose) that is welded into the valance on the outer
corners. These tube holes are cut just under the bumper, so
are fairly unobtrusive and with the angle of them look
fairly sexy anyway...
"The great thing about them (apart from the cold air), is
if you get someone to give the engine a rev while you've got
your hand over one of the intakes, you can really feel the
engine sucking! There'll be hell to pay the day I hit a
sparrow!"
AIR INTAKE MODS -- BOLT-ON VERSION: John Goodman
reports: "My (unmodified) '89 XJR-S 6.0 has different air
cleaner boxes (part numbers SPE 1008 and SPE 1009 ) with
large bore intakes. These take I believe the standard air
filters and fit the standard intake manifolds. In other
words it's all simple bolt-on improvements for any V12.
"Even more interesting is a special very neatly designed
radiator top crossbeam (part number SPD1164) which has quite
large smooth oval air intakes incorporated in it. The air
intakes in this crossbeam line up perfectly with the air
boxes.
"It all looks very neat, but they are JaguarSport parts
and won't come cheap!!!"
Regarding that top crossbeam SPD1164, Goodman adds: "I
think the part no. has been superseded with SPD 1428.
This is the part no. listed for '93 XJR-S (American spec).
The only difference AFAIK is that this part has mounting
holes for the location of the Ign power amp, (necessitated
because the manifolds were different) and rubber connecting
hose. There is a good picture of this component in Jaguar
World vol.2 no.2; anybody handy with a welder could modify a
standard one."
AIRFLOW IMPROVEMENT -- HOME MACHINIST VERSION: If
you have access to a machine shop, you can make a minor
improvement in intake airflow with little fuss. Remove the
air filter housings, and remove the butterfly housings. You
will need a #30 Torx screwdriver to remove the butterfly
housings. NOTE: The ports the hoses connect to may look
similar, but they may be different! Be sure to carefully
record which hose connects to which port prior to
disconnecting the hoses.
Referring to Figure
25, machine a rounded edge on the inlet into the
butterfly housing. This modification should not be attempted
by hand, as smoothness and consistency is important. It is
important that the radius blend smoothly into the inner
surface of the passage, but it will form an edge with the
air filter mounting surface.
Before starting, ensure that the machining will not
interfere with the butterfly seat nor with any of the vacuum
ports near the butterfly seat; by avoiding machining more
than 3/8" into the throat, problems should be averted. Also,
avoid cutting into the openings for the two bolts that hold
the butterfly housing onto the manifold; while doing so
wouldn't cause any leakage, it may cause a whistle as the
air flows past the opening. Keeping the outer diameter at
2-13/16" should be acceptable.
Enlarge the opening in the air
filter housing to 2-13/16". The gaskets typically are
already this size, but final trimming can be done after
assembly by using a razor knife before installing the
filter.
This modification has not yet been tried, so performance
improvements are unquantified. In theory, this mod can
provide an airflow improvement (and hence a horsepower
increase) of several percent. Considering the proximity of
the blanked-off section of the air filter, the improvement
may be even more significant. There should be no change in
performance other than at wide-open throttle. Since the ECU
senses and corrects for changes in manifold vacuum, no
tuning changes are required.
AIRFLOW IMPROVEMENT -- MAIL ORDER VERSION: AJ6
Engineering offers revised butterfly housings on an exchange
basis in which the entire bore is enlarged from 2-1/2" to
2-7/8" (32% airflow area increase) and larger butterflies
are fitted. Note that their kit includes low-loss foam
filters and air filter housings with enlarged openings,
fulfilling some of the other suggestions above. The kit also
includes an electronic gadget to revise the ECU response,
since the larger butterflies will behave differently than
the stock ones at a given throttle position. AJ6 Engineering
claims a 20-25 horsepower increase with this kit.
Roger Bywater points out that "...our large bore versions
have radiused entries as well so they will certainly flow a
lot more than just radiused stock items."
INTAKE MANIFOLD MODIFICATION: AJ6 Engineering
offers a service called the Plus Torque Conversion where
they cut the intake manifolds open and modify the openings
into each runner, then weld the manifolds back together.
CARBURETORS: Replacing the EFI with carburetors is
not recommended. Carburetors have several disadvantages:
First, a standard carburetor does not correct for changes in
altitude, temperature, fuel density, or other variables that
make an engine run at less than optimum performance.
Corrections usually require an excessive amount of
complication in the carburetor design.
Second, since the carburetor relies on a pressure
reduction due to drawing air through a venturi, there is
always a flow restriction due to the venturi. Using a
carburetor with a larger venturi reduces the loss, but the
airflow at idle is so small that they have difficulty
drawing fuel consistently, and a rough idle and poor low
speed performance is the result. The American solution was
the progressive 4-barrel, which uses one set of venturis at
low speed and an additional set at high speed.
Third, carburetors tend to have problems ensuring proper
fuel/air mixtures at all cylinders. With most arrangements,
the corner cylinders on a V-8 tend to run leaner, because
the path for the fuel/air mixture to get to them is more
convoluted, and the fuel gets left behind and drawn into a
nearer cylinder. Such problems would be even more serious on
a V12.
Problems occur when a cylinder runs lean; burned pistons
usually result. In the old days, the engines would simply be
adjusted rich enough to avoid any problems. When
environmental regulations and fuel efficiency demands
rendered this solution unacceptable, the incidence of burned
pistons increased.
The time-honored solution to this problem was multiple
carburetor systems. The intake path for each cylinder must
be similar, and sometimes even a dedicated barrel for each
cylinder was used (Webers, etc.).
Obviously, fixing all these problems simultaneously would
involve a truly elaborate carburetor system, possibly
requiring multiple, progressive barrels for each
cylinder.
EFI systems generally come in two types: throttle-body
and multi-port. Each type will correct the first and second
problem of carburetors, because all EFI systems
automatically correct for variables and no EFI requires a
venturi. The throttle-body system, which consists of a
single injector in the same housing as the butterfly valve,
shares the same distribution problems as carburetors, but is
much simpler and cheaper than multi-port.
Multi-port EFI, what the Jaguar comes with, is the ideal
fuel supply system. Since the injectors serve each cylinder
individually, there is little chance of a cylinder not
getting its share.
The only disadvantage of EFI is the difficulty in
modifying it -- which, of course, the EPA considers an
advantage. However, contacting AJ6 Engineering will likely
alleviate all such concerns; they will modify ECU's for very
reasonable fees.
EFI SYSTEM REPLACEMENT:
Electromotive Inc. makes a system called the TEC-I (TEC
stands for Total Engine Control) that replaces the EFI
computer and the entire ignition system as well. It's got
more modern and comprehensive electronics than the Jaguar
original, including an optional knock sensor. Also, it is
programmable using a PC-compatible computer, allowing the
owner to customize the operation to suit his needs. It's not
cheap; but if your ECU has already died and you're looking
at the cost of the Jag original to get running again, it
starts to look cheaper. And if you're having ignition
problems as well (this system renders the entire distributor
superfluous, you might as well put in a blank-off plate), it
starts to look downright reasonable.
If you are performing serious engine modifications, this
system is just the ticket. Since it can be calibrated, you
are not restricted to the original response curves on your
non-stock engine.
AJ6 Engineering also makes replacement EFI systems and
components, and will modify the stock ECU on an exchange
basis. According to Jeffrey Gram, "if experimenting was
wished they could do a single EPROM version , which has up
to 8 MAPs. It would be possible to switch between the MAPs
if the ECU is depowered between switches by means of a
"dial". AJ6 do such programmes to experimenters which then
have 8 maps to choose from trying to find the best
setting."
Scott Horner found an aftermarket system in New
Zealand:
Link Electro
243D Annex Rd
Christchurch, ph +64 3 348-8854
"From them you can buy the ECU, Ignitors, Injector
Ballast and Tuning Module (a handheld LCD interface) &
the Crank Angle Sensor... You still need to supply a lambda
sensor (aftermarket Bosch will do), and the coils...On my
car, we used VN Holden Commodore (Australian GM car) coils,
2 coil packs. The Holden uses the Buick 3.8 liter engine, so
it's presumable the coils would be available in the US in
some form. I have heard these coils only last about
20,000km, but we'll see.
"Any 3 or 6 pack coil combination would do, I have heard
Audi have a very tidy solution..."
Robert Joseph Dingli reports: "Here in Australia there
are many, many aftermarket injection ECU's available. I've
tested many of them in cars and on the bench and have found
most of them to be garbage. Common faults are production
quality, lack of temperature compensation and other
instabilities, and general difficulties with setting up a
system from scratch. Basically you get what you pay for. A
$2000 Motec or Autronics unit is highly recommended over
sub-$1000 Injec, Linx EMX, Microtec or Haltec. The expensive
units also control ignition. The Motec, Autronics and Haltec
require a portable PC (to be added to the cost if not
available) to make proper adjustments.
"As far as "high performance" chips are concerned, I'm
rather skeptical as to their worth. The problem (??) with
modern day EFI systems is that they are very close to
optimum, being a fine balance of performance, economy and
exhaust emissions. Some of the chips available advertise
that the systems will still comply with pollution levels.
The specs reveal that power increases are only in the order
of a few percent for most cars."
"Systems where chip changes may actually make a
noticeable difference are:
- Systems with electronically-governed rev limits.
- Racing use where pollution isn't a concern.
- Turbo cars where the electronically-governed boost
limits are raised.
- Electronic ignition systems without knock sensors
where the timing maps can be advanced to take advantage
of better quality fuels.
- Electronically-controlled auto gearboxes where
upshift points are raised.
- Older poorly-calibrated systems, e.g. SIII XJ6 Jags
set up for cold climates but being run in warmer
climates."
According to Ken Wallace, "If you live in a regulated
area the smog police will not approve of any of this even if
it improves your emissions. You can have your installation
certified, but this is very expensive like more than $10,000
from what I hear."
Robert Gee adds a warning about aftermarket EFI systems:
"I worked for a car manufacturer who made their own
injection systems (Rover MEMS). One or two people had fitted
MEMS to their own cars, mostly for competition use. One guy
had a modified peugeot 205 GTi with one in. He had spent a
fortune on the thing.
"Now, given that this guy had access to rolling roads,
vehicle calibration experts and the like, the driveability
was never perfect (an important Jaguar feature - low
throttle response crucial on an auto). Also he went through
about 3-4 tankfuls of petrol doing the calibration (not too
bad at US petrol prices I suppose - more than the cost of an
ECU at UK prices). And this was still with the very fine
tuning carried out automatically (This was done with some
special adaptive software we were working on which used the
lambda sensor feedback signals to adjust the fuelling
maps).
"To cap it all, when he came to sell the car it was quite
hard since it was non-standard and hence not supported by
any garages.
"Put it this way, I could have converted my XJ-S 3.6 to
full sequential injection with fully programmed ignition for
next to no cost - but preferred to keep it standard and I
probably would not have got it any better than the Lucas P
digital.
"If there one thing I learn't at Rover it's that the low
throttle drivability is what separates a good car from a bad
one - and it also takes about 95% of the engineering effort.
Anybody can make a car which goes well at full throttle -
and I suspect it's the latter market at which the after
market fuel injection systems are aimed."
IGNITION SYSTEM REPLACEMENT: Welsh Enterprises
offers at least two different models of Lumenition
electronic ignition system for the XJ-S, each featuring an
optical pickup and compatible with their engine rev
limiters. Note that these systems do not offer
electronically controlled advance; they merely replace the
existing electronic ignition with another, continuing to use
the seizure-prone centrifugal advance and the leak-prone
vacuum advance that come with the car. These kits are
terrific upgrades for points and condensers, but benefits
over the stock XJ-S electronic ignition system are probably
minimal.
NITROUS: Martin R. Fooks has a nitrous system in
his XJ-S: "The Nitrous system was supplied by Trevor
Langfield and is a customized "High Power Nitrous" system.
Because of the size of the hit to the engine (150BHP) they
installed a progressive controller, which fits neatly in my
car where the trip computer used to be. This enables me to
control the way the extra power is delivered to the engine,
such as starting power, ending power, time delay and time
from starting level to ending level.
"I am very happy with the Nitrous installation, which
really seems to be very smooth on the V12. Trevor's people
have the computer equipment to work out power and 0-60MPH
times and that is where the figures came from. As a side
note, it ran 5.3 seconds 0-60 with a standard TH400 and only
75BHP jets in the NOS system instead of the 150 jets.
"Nitrous got a very bad press in the past, caused mostly
by people adding too much power to their engines, or by not
richening the fuel mixture when the NOS was injected. The
casualties in my case have been the torque converter and the
rear IRS mounts, which were all bar 1 ripped off." (See the
notes regarding rear
suspension mount weakness.)
"The engine is stock except for the exhaust and intake,
and I have had no problems at all with it (unlike the torque
converter).
"The builders of my system told me that they do not
recommend putting any more than 50-75BHP into your engine
without using a progressive system as avoidable damage to
the engine could result.
"Their main concerns with adding 150BHP were not with the
engine as they believe it to be a very strong and reliable
item. The standard transmission and torque converter were
their main objection to the increase which as it turns out
was well founded."
"The amount of power provided in total by the NOS system
can be changed by installing new jets at an English price of
7 pounds per pair, so if 150BHP proves too much to handle,
you can always fit a smaller pair taking very little time
and expense. 200BHP is the maximum obtainable by my kit. My
suppliers stated to me that as a rule they do not fit
systems with more than 50% of the original engine power
(which is why I'm only using 150 Jets instead of 200).
Obviously this is not the case if you bullet-proof your
engine."
ADDING EMISSIONS CONTROLS: Huh? Well, Germany now
has a taxation system that penalizes cars without emissions
controls so severely that many German XJ-S owners are
seeking to retrofit. For many years the German version had
no catalytic convertors or oxygen sensors even though they
were provided in the US.
According to Jeffrey Gram, the following outfits (all in
Germany) will install emission controls in cars that were
not originally equipped with them:
- Ernst Apparatebau, Hagen, Tel +49 (0)2331 3600-0
- GAT-Abgastechnik, Gladbeck, Tel +49 (0)2043
24021
- Gutmann, Breisach, Tel +49 (0)7667 1091
- G+M Kat, Gladbeck, +49 (0)2043 42410
- HJS Abfgastechnik, Menden, +49 (0)2373 9870
- Oberland, Garmisch-Partenkirchen +49 (0)8821
1036
- Oettinger, Friedrichsdorf +49 (0)6172 7053-55
- Walker, Viernheim, +49 (0)6204 738-0
- Waschkuttis, Wiesenthau, +49 (0)9191 96495
- Wurm, Stuttgart, +49 (0)711 420071.
CAMSHAFT REPLACEMENT: Most performance enthusiasts
will agree that replacing the camshaft (or camshafts; the
Jag V12 has two, some cars have four) is the most effective
way to change the performance of an engine. The entire
personality of a car can be radically altered by merely
changing the camshafts.
Chad Bolles reports that Isky makes high performance
camshafts for the Jaguar V12.
Rod Beere Racing Services also offers hot cams, as well
as tappet shims in extreme thicknesses that may be necessary
for such installations.
Note that any camshaft alterations should be accompanied
by an EFI system modification; there will be increased
airflow at wide open throttle, but since the feedback
circuit is disabled under those conditions the fuel supply
will remain at the original fixed map with no trim. The
engine will therefore run lean at full throttle, a situation
that begs for burned pistons and valves.
There has been some confusion regarding the difference
between pre-H.E. and H.E. cams, since published valve timing
data on the two engines seemed to differ. However, Bywater
points out that they actually use the same part number
camshafts. "When the V12 was launched the valve timing was
quoted in Walter Hassan's SAE paper 720163 as being
17,59/59,17. When the H.E. version was launched in 1981 the
supplement to the manual quoted cam timing as 13,55/55,13.
In fact, the same cam profile had been in use since the
early 1970s and continued through into the 1990s under part
numbers C42176/7, therefore all EFI V12s were produced with
these cams. Now it is not widely known that for some time
the V12 was mildly plagued with excessive tappet noise and
in the course of dealing with the problem the quietening
ramps on the cams were altered at least once around 1972-3.
I was personally involved in an investigation into the
causes of a spate of tappet noise around 1978 and am not
aware of any cam change ever being made to the V12 in
production for any other reason than to reduce valve gear
noise.
"Measurement of true cam timing is not a straightforward
matter and it has been accepted practice to measure from the
point where the quietening ramp ceases and the lift curve
proper commences. For those who are not familiar with the
term, a quietening ramp is an area at the flank of the cam
where the rate of lift is small, at around 0.0005" per cam
degree, and to be fully effective must extend rather higher
than the widest clearance likely to be encountered. The idea
is that any reasonable running clearance found in use it
will always be taken up at a predetermined velocity which
should not give rise to noise. If the ramp geometry is
changed, as we know happened on the V12, then the timing as
measured at the top of the ramp could also vary and this
accounts for the small difference of timing quoted at
different times in its life."
Mike Cogswell elaborates: "Duration itself can be
misleading, since almost nobody measures duration from the
instant the valve leaves the seat until the instant it
returns. Instead, duration is commonly measured at some
point where there is noticable flow, albeit typically a very
low fit. This is important, since different cam grinders
measure duration at different lift, hence one man's long
duration might be less than another's short duration. Caveat
emptor, as always."
Bywater again: "It is perhaps of interest to note that
over the years Jaguar used virtually identical valve timing
on all their mainstream engines. Consider the
following:
SS 2.5 & 3.5 litre 16,56/56,16
XK 3.4,3.8,4.2 15,57/57,15
V12 17,59/59,17 (13,55/55,13)
Clearly having found something that worked there was
great reluctance to change from it, although the smaller
displacement engines often had softer timing to beef-up the
low speed torque as the following examples show:
SS 1.5 litre 10,50/50,10
XK 240 saloon 10,50/50,10 (5/16" lift)
Note also that hot cams might not have the expected
effect. AJ6 Engineering (page *) once
offered a milder cam than stock, and the result was
higher mid-range torque and a nearly one full second quicker
0-to-60 time. Bywater explains: "...we introduced some short
duration cams for the V12 back in about 1984. They certainly
boosted mid-range performance, especially appreciated with
the 3 speed BW and GM transmissions, but suffered a
marketing problem because they gave slightly less peak power
so we eventually discontinued them. We sense that attitudes
are changing and many drivers are realising that a
performance gain around 40-70 m.p.h. is far more valuable
than adding to a rarely seen top speed so we may well offer
a modernised version of such a camshaft again in the near
future."
VALVE ADJUSTMENT (!):
Roger Bywater of AJ6 Engineering (and formerly with Jaguar)
says, "we knew back in the 1970s that running with the
exhaust valve clearances set at 0.016" gives a slight but
measurable gain in mid-range torque and reduced fuel
consumption. Noise is not excessive at this setting because
the actual running clearance closes up with the higher
temperature of the exhaust valves compared to the inlets
which must be set as normal.
"Anyone wishing to measure a V12 cam, as I have done in
the past, will find that the timing quoted for the H.E.
occurs at 0.010" lift whilst the timing at the point at
which 0.012" clearance is taken up is an almost unbelievable
36,78/78,36. The difference in overlap between 0.013" and
0.016" clearances is about 12 degrees so the need to avoid
tight clearances will be obvious and although the extra lift
may be insignificant it can profoundly effect the HC
emissions generated, quite apart from the modest effect on
torque. In my view the best compromise regarding noise and
performance is to aim for 0.013" for inlets and 0.015-0.016"
for exhaust which, because of greater expansion of the
exhaust valve stem, results in a similar true running
clearance for both.
"...If mid-range torque could be improved by just opening
up the clearances, why did the factory not do it in
production? Well maybe they did (I am not prepared to be
more positive than that) -- but you will not find any manual
telling you so because the reason for doing it would have
been to reduce HC emissions at a critical time, at the risk
of introducing more tappet noise problems."
CAM COVERS: Strictly an appearance mod here. Some
of us think those Jaguar decals on the cam covers are not in
keeping with the general class of this automobile. One
suggestion is to remove the decals and attach some brass
insignias with screws -- making sure not to cause a leak.
Might even find just the right key fob to use.
A suggestion from Steve Averill: "If you want to find
something a little better looking that the Jaguar decal on
the valve cover, why not either get it photo etched or
alodyned? That'd be more apropos than sticking on something
that'd probably wind up looking "tacked on" & you could
pick any pattern that appeals to you."
If you have them off anyway and have a milling machine at
your disposal, you might consider skimming the top of the
ribs, leaving the black paint in the grooves between the
ribs. It'll really make it look snazzy.
SO YOU'RE DOING A VALVE JOB: To many of us, doing
a valve job means pulling the heads off the car, taking them
to a machine shop, picking them up later, and bolting them
back onto the engine. However, the valves are a prime place
for easy improvements when the heads are off. I will mention
a few ideas.
The valve guides are sleeves that are press-fit into the
heads, and protrude a little bit into the inlet and exhaust
ports. Jim Isbell suggests that, before you install the
valves, you take a hand grinder and grind off the protruding
parts of the guides flush with the surface of the port.
The valves and seats on the Jaguar V12 are supposed to be
machined with 44‡† angles. Most machine shops will suggest
that the seats be "triple cut", in which additional cuts are
made at angles greater and less than 44‡† in order to
control the width and location of the contact area. Typical
angles for these cuts would be 32† and 60† and the contact
area width should be about 1‡ mm wide. Chad Bolles suggests
that a similar triple cut on the valves themselves would be
beneficial.
John Milne suggests that, after the valve contact
surfaces have been machined, some machinist's bluing be
applied and the valve trial fit to determine the location of
the actual contact on the valve surface. Then, carefully
avoiding the contact area, the inner edge of the machined
surface should be blended to form a smooth continuous
surface with the "tulip" shape of the valve. This helps the
flow through the valve, since it makes a smooth passage
instead of that corner. It also slightly enlarges the
opening, since the smallest flow area when the valve is open
is between this inner corner and the seat. "It's kinda like
getting a little extra valve lift for free." Blending the
inner edges of the machined surfaces of the seat may have
similar benefits.
Of course, every high-performance enthusiast will suggest
that you do a little "porting" while you're in there. This
means carefully enlarging the intake and exhaust passages.
In the case of the intake passages on the Jaguar V12,
however, this may produce undesirable results. These intake
passages are designed to provide a certain amount of
resonance-induced flow enhancement, and this requires that
the flow rates be fairly high. Enlarging the ports makes for
slower flow, which means better flow at high RPM but less
boost at low RPM. In other words, enlarging the intake ports
may increase high-speed horsepower at the expense of
low-speed torque.
The next automatic suggestion is "polishing". Quite
literally, the passages may be polished using successively
finer abrasive compounds until a mirror finish is achieved.
This supposedly will reduce surface friction of the
flow.
Before you reinstall the head, Jim Isbell suggests you
"cc" it. This means that you measure the volume of each
combustion chamber, and grind a little metal away here and
there to make sure they are all the same. This makes for a
smooth running engine. To measure the volume, you can set
the heads upside down on a level surface and fill each
chamber with a carefully measured amount of light oil.
Cc'ing must be done after the valves are installed for
the final assembly. Clearly, if valves are ground or
relocated after cc'ing, they will sit at a different level
than they did before and this would significantly change the
volume of the chamber. And this is the reason that cc'ing is
recommended whenever the valves have been redone.
TEFLON VALVE STEM SEALS: Michel Carpentier says,
"Teflon valve seals are the way to go. They last forever,
plus you can fit them on the exhaust guides as well. Less
blow-by, reduced crankcase pressure, no more oil leaks, and
cleaner oil to boot.
"Our engines came from the factory with 24 valves but
only 12 valve stem seals. Jaguar probably realized that the
British rubber intake rendition would soon fry on the
exhaust side.
"Why would any (effective) exhaust valve seal affect
crankcase pressure? When the exhaust valves open, gases gush
out of the combustion chamber with tremendous pressure. Even
though the valve itself acts as some sort of an umbrella,
there is still a significant pressure differential between
both sides of the exhaust guide. Any clearance between valve
and guide will let exhaust gases into the crankcase area.
Jaguar old trade secret to keep engines leaking oil!"
Of course, the decision to switch to Teflon seals, and to
install 24 instead of 12, may not be quite that simple. This
author had some discussion on the phone with the rep at
Silver Seals about the differences between Teflon valve stem
seals and normal nitrile seals. There is apparently a
functional difference: the nitrile seals always leak, and
the leakage allows a small amount of oil down the valve
guides to lubricate them. The Teflon items will not leak, so
the valve guides run dry. According to the rep, this is a
problem on some cars and not a problem on others. I'm
betting it's not a problem on the Jag, since it uses good
materials on both the valves and guides. Also, the action of
the cam on the tappet applies no sideways load to the valve
stem, as there is in any valve train with rockers. Still,
recognize that you may be trading oil burning for faster
valve guide wear.
Does anyone make Teflon valve stem seals for the XJ-S?
Carpentier: "Perfect Circle does, although unwittingly since
I doubt they ever considered Jaguar engines as a possible
application for their product. Our valve guide diameter is
0.502 to 0.501 in, that's essentially 1/2" or sixteen (16)
thirty secondths of an inch. Valve stem diameter is 0.3092
to 0.3093 in, and that's within 3 thou of 5/16" or ten (10)
thirty secondths of an inch. These dimensions are a bit
unusual but luckily match those of the first generation
Chrysler Hemi engines. Call Perfect Circle (they are a DANA
subsidiary) and they will tell you: "Yes, we manufacture
such Teflon seals, part number D1610, available at any NAPA
auto store".
"There is a catch: if you go to NAPA and ask for this
reference, they look it up in their computer and tell you it
does not exist (never mind telling them what kind of car it
is for...). The last time I was in the US, I finally found a
place in Los Angeles that would order them for me. The seals
actually came from a company called Silver Seals
Products/Whip-L Products, Trenton, Michigan, 1-800-521-2936;
their reference is DT1610 but the seals carry the Perfect
Circle logo." This author called that 800 number, and had a
set of 24 Teflon valve seals on order in a matter of minutes
and in hand in a week at a cost of less than a dollar each.
For those outside the US where an 800 number won't work,
their regular phone number is +1 (734) 479-2255.
The OEM nitrile seals on the inlet valves are pressed
over the valve guide until they snap into a groove around
the guide just above the surface of the head. The exhaust
valve guides have no such groove. This turns out to be a
non-issue with the Teflon seals; these seals press fit onto
the OD of the valve guide, and therefore do not use the snap
groove. While the OEM seals are a simplistic piece of
rubber, the Teflon seals include a metal ring on each
diameter to provide a secure fit on the guide and on the
valve stem itself.
Besides the diameters of the guide and stem, there are a
few other things to consider whenever fitting a non-OEM
valve stem seal to an engine. In this case, the OD of the
base fits within the inner spring just fine. The Teflon seal
is a little taller than the original seal, which makes for a
really close fit; the valve lift is 3/8", and that's pretty
much right where the valve keepers sit down on the top of
the seal's lip. If you intend to run an aftermarket cam with
more lift, you'll need to either use the shorter OEM seals
or make some other changes, like shortening the keepers or
the guides.
Installation is not as simple as with the nitrile seals.
Carpentier: "You cannot push them in as you would plain
vanilla seals. With your package you should get a clear and
rather flimsy plastic tube closed at one end. Slipped over
the valve stem, it protects the seal as you first push it
over the stem end (push with your thumb with a slight
rocking motion to get started) then slide it over the cotter
groove. Trim this sleeve so it still covers the groove but
does not stay trapped under the seal when fully home." Note:
on the valve stems, just below the groove, the part number
is engraved; might as well leave the sleeve long enough to
cover the number too, just to make sure you don't damage the
seals going over it.
"When you start, remember (24 times!) to put the spring
seat first as it does not fit over the seal. This is
especially important as a teflon seal cannot be removed
without being destroyed: 1) it is hard to pull it from the
guide without distorting it and 2) as it goes back over the
cotter groove, the sealing surface between stem and seal
will be damaged." Clearly, you need to have the valve in
place before installing the seal and you can't remove it
afterward, so make sure you are actually at the final
assembly stage (all lapping completed, etc.) before
installing seals.
"Now you need to push the seal over the guide. Use a tube
(e.g. a deep socket) with ID greater than the narrow upper
section and a rubber mallet. A first blow will get you over
the guide chamfer, then tap it all the way in. Don't hammer
too hard though or the upper portion will shear off as you
hit bottom." Note: this author has done this job, and it's a
lot easier than it sounds.
EXHAUST FLOW LIMITATIONS: Roger Bywater explains
an inherent shortcoming of the H.E. engine: "The small and
pocketed exhaust valves are the real problem and is why all
the high performance racing V12s have been based on the old
"flat head" design. Putting big exhaust valves in doesn't
help because the chamber walls are so close and leave no
room for flow around the edge of the bigger valve head. In
fact if the HE were not of abnormally high compression
ratio, always a useful trick to get a bit more top end power
out of an engine that doesn't breathe, it would struggle to
produce the barely adequate power that it gives as standard.
You can build an HE to 6 or more litres (we used to do a 6.3
using 98 mm bore and standard crank) but all you really get
is more torque low down but not much more power."
TOTAL SEAL PISTON RINGS:
Total Seal, Inc., makes a type of piston ring set in which
the second ring is a two-piece ring. Effectively, it puts
two rings in a single groove with the gaps staggered -- so
gases cannot pass either gap. As a normal ring wears, the
gap gets larger and the leakage increases accordingly. With
Total Seal rings, the gap is covered by the second ring, so
it won't leak no matter how much it wears.
Apparently, these rings are highly recommended by just
about everyone who has ever used them -- including high
percentages of competitors in several types of racing.
Testing shows considerably less leakage even compared to new
conventional rings. Not only will performance improve, but
the reduced blowby should result in less contamination of
the oil.
MAJOR ENGINE MODS: The Jaguar V12 H.E. engine is a
technically advanced powerplant. It is recommended that
major engine modifications such as enlarged bore or stroke
be attempted only by knowledgeable and experienced
performance enthusiasts.
Changes to the engine displacement would require
modifying or replacing the EFI. The stock EFI is hard to
modify; it has a fixed (trimmable, but fixed) program for
intake manifold vacuum and RPM versus fuel. If the
displacement is altered, this relationship changes. One
solution is an aftermarket EFI system that is completely
programmable and re-programmable (see above). Most choose to
ditch the EFI at this point for carburetors, beginning the
problems outlined above. And, the emissions inspector will
not smile at them.
With an advanced combustion chamber design, the H.E.
engine has 11.5:1 compression and runs on 89 octane unleaded
(Unleaded Plus). Almost any mods to the engine internals
would endanger the integrity of this design, and the owner
would risk having to lower the compression radically and/or
face buying octane boosters ($$$). His fuel economy would
get worse, and if he didn't do his job right, his
performance would get worse, too.
One modification worth considering is to install the
European pistons, raising the compression to 12.5:1. This
will obviously require higher octane fuel. The European XJ-S
H.E. reportedly produces about 30 more HP than the US
version. According to Chad Bolles, the only difference in
the engine is the piston, which has a slightly different pin
bore location.
ENGINE ENLARGEMENT: There are two ways to get more
power out of an engine: tune it to obtain more horsepower
per liter, and enlargement to provide more liters. Of the
two, enlargement has some definite advantages: if the
horsepower per liter is not changed significantly, the
durability may not suffer; the "manners" of the engine,
important in street applications, may remain as stock or
even improve; fuel economy may remain nearly unchanged; and
the use of higher octane fuel or octane boosters may not be
necessary.
Indications are that the Jaguar V12 has a lot of
room for expansion. A 5.3 liter (90mm bore x 70mm stroke)
for two decades, it was enlarged by Jaguar in the early 90's
to 6.0 liter (90mm bore x 78mm stroke). AJ6 Engineering once
offered engines bored and stroked in sizes up to 7.1 liter
and 405 BHP.
The room for expanding the bore seems to be limited to
around 98mm. The stroke, however, can go a long way, and
since it is so over-square to begin with, getting too
under-square is not a problem. Bill Whitehas prepared a
Jaguar V12 for use in a 3/4-scale replica of a Spitfire
fighter plane. He expanded the bore and stroke to 96mm x
95mm -- almost an inch of additional stroke, for a
displacement of 8.4 liters! This was done without
significant modification to the block, and the stock H.E.
heads were used. At 3000 rpm, this engine produces 500 ft-lb
of torque in naturally-aspirated form, and 820 ft-lb when
supercharged as it is in the aircraft.
According to White, that isn't the limit by any means. He
reports that an outfit in the UK called Forward Engineering
prepares Jaguar V12's for use in offshore racing boats. They
install a spacer 3/4" thick between the block and the head,
and use liners the same amount longer than stock to provide
longer cylinders. Longer studs hold the head on, and since
3/4" is the length of a link of the timing chain the
addition of four links allows an otherwise completely stock
timing chain scheme to be used. White says the engines so
assembled are 9.3 liter, and are very successful at offshore
boat racing.
ALUMINUM CYLINDER LINERS: Apparently aluminum
cylinder liners are available for the Jaguar V12 from GKN
Squeezeform in the UK. Such use would require the
replacement of the pistons as well, since the stock pistons
are designed (via the use of a special alloy, as well as
steel expansion-control inserts) for the expansion rate of
the stock iron liners.
Jeffrey Gram contacted Rob Beere Engineering, which
reported: "In the 1980's the Jaguar Group C endurance racers
used aluminum liners. It is actually not pure aluminum but a
compound called nickasil or similar. This material is very
light and is treated (don't know with what). In 1986-1988
the alu-liners were not used anymore for endurance races
since the wear was too big and inferior to cast iron.
Apparently this nickasil material has a tendency to pick up
material by which the pick-up process is accelerated and the
material wears out quickly. The nickasil was only used on
race engines with frequent liner renewal."
The V8 engine used in the XK8 and XJ8 comes with nickasil
cylinders.
SEEEEERIOUS ENGINE MODS: There have been
experiments to adapt the 4-valve DOHC head from the Jaguar
AJ6 2.9 engine to the V12. The cylinder spacing and bolt
patterns are the same -- according to Roger Bywater, not
because the AJ6 was derived from the V12, but rather because
there was a plan to put the V12's H.E. head on some versions
of the AJ6. If the DOHC heads are just bolted onto the V12,
on one side the intake ports will be on the outside and the
exhaust ports will be toward the center -- not good. So, one
of the AJ6 heads must be turned around backwards -- and some
complicated fabrication work is required to get such things
as the cam sprockets rearranged. Bill White appears to be
reviving this idea, and since he generally does good work
he's likely to produce an attractive product.
Steve Averill reports that the Autumn 1988 issue of
Jaguar Quarterly has an article on "a 60 valve DOHC V12 that
was under development by Warrior Automotive Research. They
expected to achieve 100 bhp/litre in low tune with a 5.8l
engine. The head had 3 inlet & 2 exhaust valves per
cylinder." No word on what's happened since, but Warrior's
phone number was given as 061-928 3284 in Cheshire if anyone
wants to try a call.
There has been at least one experiment in Australia in
turbocharging the XJ-S, but the results were apparently not
good. Officially the problems were blamed on the inability
to assemble a drivetrain that would handle the 1000+ hp for
more than a few seconds.
Chris Sleeman (also in Australia) reports on a 1998
endeavor: "When I picked up my Daimler Double Six yesterday
from my local Jaguar specialist, he showed me an XJ-S he is
working on. It is a '76 model, with a 6.8 Litre Twin Turbo
V12. The motor was built by them, and the customer is
apparently going to enter it into the Targa Tasmania in
April. The motor is being dynoed next week, but they say it
puts out around 700hp. It is running 0.8 bar of boost at the
moment, and will be using Motec injection."
AIR INJECTION SYSTEM: Removing
the system that injects air into the exhaust system is not
recommended, as this would obviously be a modification of an
emission control system and would be illegal in many areas.
Too bad, too; this system accounts for a great deal of
plumbing under the hood as well as a belt-driven load on the
engine. And it only functions when the engine is cold -- the
pumped air is wastegated after the engine warms up to
prevent interference with the operation of the oxygen
sensors. And removal would be so easy: making a bracket and
mounting a standard Ford adjustable idler pulley in place of
the pump, being sure to mount the idler low enough that the
belt clears the fan belt idler (a different A/C belt would
be needed); and plugging the holes in the intake
manifold.
Of course, some people insist on genuine Jaguar parts.
Peter Smith: "I removed my air injection system and used a
jockey pulley to carry the V-belt. These pulleys were
standard equipment on English cars which did not have to
meet emission requirements in the early days and some of
these jockey pulleys may still be available in wrecking
yards in England." Smith went on to provide enough data from
the parts books to create a parts list:
C36014 Pulley
C37886 Hub
C37889 Bearing
C23128 Setscrew
C37879 Bearing Holder
C37875 Bracket
...plus an assortment of generic bolts, nuts, etc., that
you can get locally. Here's a guess: judging from the
drawings, it's entirely probable that the pulley used as an
idler is the very same part that's used on the air pump --
so you may be able to skip buying C36014.
If you happen to be using your car
for competition or other applications where the air
injection system is unnecessary, John G. Napoli devised a
method for replacing the air pump with a GM alternator,
allowing the elimination of the Lucas alternator and
eliminating one of the four belts on the XJ-S. Since a GM
alternator hardly costs any more than an idler pulley (!),
it's a low-cost mod. And if your Lucas alternator is acting
up, it will assuredly save you $$$. His description
follows:
"First, remove the original alternator. The original
Lucas unit then gets tossed." Note: you might wanna just
store it -- the guy you eventually sell the car to might
wanna return the car to original condition for some
reason.
"I elected to use what automotive electrical rebuilders
refer to as a ëlarge case GM 70 amp alternator with 12
and 6 mounting'. Obviously, this should not have a
serpentine belt pulley; a standard GM V-belt pulley is
needed. This unit is available up to 100 amps. (You could
probably use some other alternator.) The cost of this
rebuilt alternator at my rebuilder was $30.00 (US) with no
core charge. And a replacement, should one ever be needed,
is as close as any auto parts store." Note: be sure the GM
alternator selected has an internal regulator.
"The air pump and its vacuum valve get tossed, too. Now,
take the steel bracket that supported the base of the air
pump. Take a piece of flat steel or aluminum sheet (I used
aluminum) about 5/32" thick (you want stiffness but too
thick and you'll need longer bolts, and who needs the extra
weight) to use as an adapter plate. The piece should be as
wide as the stock air pump bracket and twice as long
(high).
"The idea is to use the stock air pump bracket to secure
the alternator right side up in its new position, shifted
ëdown' one set of bolt holes to mount the alternator a
little lower in the engine bay for thermostat housing and
radiator hose clearance.
"The stock air pump bracket has four bolts that secure it
to the side of the block (via an aluminum block bracket
casting itself attached to the block with two large bolts).
The plate you'll make will be drilled for six bolt holes,
and is mounted sandwiched between the alternator (via the
steel air pump bracket) and the block bracket. The upper two
holes are used to bolt the adapter plate to the upper two
holes of the block bracket. The middle two holes are used to
bolt the air pump bracket and adapter plate to the lower two
holes of the block bracket. The lower two bolt holes of the
adapter plate bolt the air pump bracket to the adapter
plate. Got it? Use the air pump bracket as a pattern for the
bolt holes on the adapter plate.
"Bore a large hole in the top center of the adapter plate
to clear the forward bolt that attaches the block bracket to
the block -- once again, use the air pump bracket as a
guide. If you made the adapter plate too wide, notch it to
clear the alternator (nee air pump) adjusting bolt. Polish
the adapter plate to a high gloss to add several miles per
hour. Make a spacer that fits between the lower alternator
mounting lug and the back of the air pump bracket, so that
the lower pivot bolt can snug everything up.
"Mount the adapter plate and air pump bracket on the
engine. Take the brass terminal lugs off the Lucas
alternator and transfer them to the GM unit. Loosely bolt in
the GM alternator, using the stock air pump adjuster. You
will see that the alternator will line up perfectly with the
plane of the A/C-air pump belt.
"Now the aggravating part: remove all the belts! Toss the
original alternator and air pump belts. Buy a belt 2 inches
shorter than the stock A/C-air pump belt. Install this new
belt and reinstall the power steering and fan belts. Tighten
the alternator.
"If you have a GM alternator plug, use it for this next
step. Otherwise, standard solderless connectors (which I
always solder and insulate with heat-shrink tubing) can be
used providing they are well insulated to prevent
accidental grounding to the case of the alternator. The
original Jag idiot light sensor wire goes to terminal 2 of
the GM alternator. Hot wire terminal 1 of the alternator to
the ëbattery' terminal of the alternator. (This does
not seem to be a parasitic current draw problem -- if you
prefer, wire a relay thru the ignition circuit so this
connection is only ëhot' when the ignition is on.) Plug
in the two main Jag alternator leads to the ëbattery'
terminal via the brass lugs you transferred from the Lucas
unit.
"Plug the air pump hoses in the air cleaner and the
exhaust manifolds as needed. Replace the battery cable,
radiator hose and air cleaner. Start it up, watch that baby
charge, stand up straight, get the kinks out of your back,
and feel proud of yourself.
"Notice that you have picked up 300 or 400 rpm of idle
speed. Readjust the idle. Note the number (length) of the
new alternator belt and scratch it into the fender of the
car. Alternately, write it down and keep it in the glove box
or trunk."
Michael Aiken points out that if you started with the
Bosch 115-amp alternator instead of the Lucas, you will be
reducing your capacity with this mod -- and the Bosch seems
to be far more reliable than the Lucas, so you may not be
improving reliability significantly either. The loss of
generating capacity is not likely to cause problems unless
you have something added to your car that uses a lot of
juice. The removal of the air pump and the reduction in the
number of drive belts may still justify the mod.
Napoli offers a suggestion for plugging the air injection
holes in the intake manifold: "Buy 1/4" nail anchors from
Home Depot. They are aluminum and look like a large pop
rivet. Get them 1" long. Cut them back to 5/8" long with a
band saw or hack saw (only cut the body, don't worry about
the ënail'). Put the two o-rings from each air tube on
the shank of the anchor. Smear on some engine-grade
silicone. Insert into the manifold and hammer down the nail
all the way. Omit the ëplates' and retighten the intake
manifold to the engine. Looks great and works great."
EXHAUST SYSTEM: The stock XJ-S exhaust system is
quite restrictive, especially the area right around the
oxygen sensors. However, there appears to be little
available in the way of aftermarket exhaust systems, other
than stainless steel systems similar to the stock system.
There is probably not enough room under the hood for a
header. To improve exhaust flow, there appear to be few
options other than custom-making your own system -- a real
challenge, considering the spaces to work with.
One option is to add a crossover pipe: a connection
between the dual exhaust systems to permit each exhaust
pulse to escape through both systems. This method has been
used with dramatic results on V8's, and some cars come with
them now. To avoid screwing up the EFI, the crossover should
be after the oxygen sensors; but the closer it is to the
engine, the more effective it is.
It should be noted that the improvements would not be
expected to be as great as on a V8; six cylinders per bank
results in smoother exhaust flow than four, so the benefits
of a crossover are smaller. However, the Series III E-type
WAS fitted with a crossover pipe, so it must have had some
benefit.
A crossover has two disadvantages: First, it can make the
exhaust system, already a pain to work on, even more
difficult to assemble and disassemble. Second, being able to
check the exhaust from each bank helps with engine fault
diagnosis. Both of these problems can be minimized by
including a flat face flange in the crossover, and making a
flat blank-off plate that can be bolted into the connection
when doing engine analysis.
Another option is to replace some of the mufflers with
straight pieces of exhaust pipe. Obviously the car would
leave the realm of the totally silent, but perhaps a little
exhaust sound is acceptable.
It is not recommended that the catalytic converters be
removed to improve performance. There would obviously result
a discussion with the emissions inspector. Furthermore,
tests have indicated that the convertors don't offer much
restriction, so benefits would be small. The only good
reason that ever really existed for removing convertors was
to allow the use of cheaper leaded gasoline, but that
benefit has all but disappeared.
OIL COOLING: The standard oil cooler on an XJ-S is
a bypass unit, meaning it only cools the oil that doesn't go
through the engine. However, as pointed out by Bob Tilley,
the XJ-S sold in Germany is fitted with a full flow oil
cooler system, and the parts are available through Jaguar.
We can make assumptions about why the German cars would be
different than other cars, possibly involving those
Autobahns.
John Goodman adds, "it's worth pointing out to others who
own later model V12's who may not be aware that all
V12 HE engines after engine no. 8S44317 had full flow oil
cooling, can't remember the year this was introduced."
Both oil systems, as well as almost any other in
automotive use, work like this: Oil is drawn from a pickup
in the sump into the oil pump. From there it goes to a
pressure relief valve, which relieves enough of the oil flow
to prevent excessive pressure in the system. The relieved
oil goes back to the sump, while the remaining pressurized
oil goes through the filter (which has its own bypass in the
event of clogging) and into the galleys that feed the
bearings, cam followers, and other parts of the engine
requiring lubrication.
In the basic bypass oil cooling system in the Jaguar V12,
only the oil that is relieved by the pressure relief valve
is piped to the oil cooler in front of the radiator, and
from there back to the intake of the oil pump. In the full
flow system used in German cars, the oil destined to go to
the galleys is piped to the oil cooler at the front of the
radiator and then back to the relief assembly to continue
through the filter and into the galleys.
Physically, the distinction is like this: in the bypass
system, oil feeds out of the outlet elbow at the bottom
front of the relief assembly to the right side of the
cooler. From the left side of the cooler, it goes to a
fitting on the bottom front of the sandwich plate on the
crankcase. It doesn't simply return into the sump here, but
instead goes directly into the inlet elbow on the bottom of
the oil pump. Hence, the oil pump actually draws suction
from two places: the sump pickup and the return from the
cooler.
In the full flow system, oil to the cooler starts at the
relief assembly as well, but at a different place on it --
higher up on the front, from one of a pair of fittings that
don't exist on the bypass relief assembly. This feed is
piped to the right side of the cooler. From the left side of
the cooler, it goes back to the other fitting on the relief
assembly. The oil pump therefore has only one intake, from
the pickup in the sump, and there is no opening in the
bottom of the sandwich plate.
The bypass system has an inherent shortcoming in that it
tends to vary the amount of cooling incorrectly. When the
oil is cold, it is also thick, and the pressure relief valve
has to bypass a great deal of it in order to limit the
pressure. As a result, flow through the cooler is high --
precisely when not needed. On the other hand, when the oil
is hot and thin, very little or none at all is bypassed, and
hence flow through the cooler is minimal -- precisely when
it is most needed.
The full flow system always flows the oil through the
cooler before it goes through the engine, so there is always
cooling. And, the coolest oil in the system is the oil fed
to the galleys, so it can be expected to reduce the
incidence of burned bearings.
If you wish to incorporate the full flow system to a car
that didn't come with it, you will need the following parts.
The corresponding part numbers for the bypass system are
also shown:
Part
|
Bypass p/n
|
FF p/n
|
Oil Suction Pipe
|
C35512
|
EAC6424
|
Oil Suction Elbow
|
C33869
|
EAC6422
|
Oil Suction Elbow Gasket
|
C31063
|
C31063
|
Relief Assembly
|
Unk
|
EAC6398
|
Relief Outlet Elbow
|
C38802
|
EAC6789
|
Oil Cooler
|
C43923
|
CBC2692
|
Oil Feed Pipe
|
C38075
|
CBC2691
|
Oil Feed Pipe
|
N/A
|
EAC8956
|
Oil Return Pipe
|
C38074
|
CBC2690
|
Oil Return Pipe
|
EAC1380
|
EAC8954
|
Retainer
|
N/A
|
EAC6413
|
Bracket
|
Unk
|
EAC6414
|
Clamp
|
Unk (1)
|
EAC6800 (2)
|
Sleeve
|
Unk (1)
|
EAC6790 (2)
|
Bracket
|
Unk
|
EAC6419
|
Plus a few bolts, nuts, O-rings, etc., all of which can
be purchased locally. If you're the industrious type, you
can probably improvise all those clamps and brackets
too.
A different sandwich plate, without the opening for the
oil return, is also required, but I don't know the part
number. It is probable that most would prefer to simply make
a blank-off cover for their existing sandwich plate rather
than pay for a new one anyway.
Now for some hints that may make the job easier. To
install all these parts would require pulling the sump off
the engine to replace the oil suction pipe, oil suction
elbow, and the sandwich plate itself. However, in theory
anyway, these replacements may not be necessary, and the
retrofit might be accomplished without pulling the sump. The
difference in the oil suction elbow is that the one for the
bypass system has the second inlet on it, and this inlet is
readily accessible via the opening in the bottom of the
sandwich plate. If this second inlet is securely plugged, it
will serve the purpose of the EAC6422 part. This can be done
by making a suitable part that plugs both the second inlet
on the oil suction elbow and the opening in the sandwich
plate, or by using a separate plug -- perhaps like the
rubber expansion-type freeze plugs -- on the suction elbow,
along with a simple blank-off on the sandwich plate. This
would not only reduce disassembly requirements, but it also
eliminates the need for purchasing a new oil suction pipe,
oil suction elbow, gasket, and sandwich plate.
Note that the difference in the oil suction pipe -- which
is, in fact, the pickup -- is unknown. But there is no
reason to believe the one designed for the bypass system
won't work properly for the full flow system. Perhaps the
design was changed slightly to fit the revised oil suction
elbow.
FLYWHEEL INTERCHANGABILITY: According to Mike
O'Neill, the bolt pattern for the V12 flywheel is the same
as the bolt pattern for the 6-cylinder Jaguar XK flywheel. I
dunno what use this info may be, since the starter ring gear
and other features are not the same; it is included
here for general info.
TORQUE LINK: When the engine/transmission turns
the driveshaft, the reaction is a twisting force trying to
tilt the engine/transmission assembly on its mounts. There
are only three mounts, two soft rubber mounts under the
engine and the complicated spring assembly under the tranny.
The tranny mount really does little to counter this force;
the torque is entirely taken by the two motor mounts.
Since the mounts are soft, the torque can move the engine
around quite a bit. If the car is not stock and producing
more torque than originally intended, the left-side mount
may actually be damaged since it is put in tension under
extreme conditions.
A racing trick is to add a fourth connection between the
engine and the chassis. By adding a link, torque can be
taken up before the engine moves very far or stresses the
mounts too much. Newer FWD cars are usually designed with
such a link, but front-engine/rear-wheel-drive cars
typically rely on rubber in tension.
Under torque, the engine twists, which means the top
moves to the right, the left side moves up, etc. A link can
be added anywhere that restricts this movement, but it is
usually preferable to put it either on the left side of the
engine connecting downward to the chassis, or from somewhere
near the top of the engine connecting to the left side of
the compartment. Either of these locations puts the new link
in tension (preferable for such parts) and helps keep the
motor mounts in compression (protecting the rubber).
Backyard mechanics have been known to accomplish this fix
by bolting a length of chain between the left-side exhaust
manifold and the chassis. Under normal conditions, the chain
is slack and does nothing but rattle. When the engine tries
to lift, the chain pulls tight and stops the motion. This
method does work, but it is hardly a suitable fix for an
XJ-S; the chain makes too much noise, and the sudden jolt
when the chain gets tight is not conducive to an impressive
ride.
To do a professional job, a better idea is to install a
link made from threaded rod with some rubber bushings
(available at any auto parts store), washers, nuts, and some
fabricated brackets to provide holes for the bushings to fit
into. Rubber bushings are essential, since a rigid
connection would transmit vibration directly to the chassis.
If necessary, shield the rubber parts from radiant heat from
the exhaust system.
Alternatively, the ingenious mechanic may find a way to
make a link from one of those FWD cars fit.
It should also be noted that the motor mounts on the XJ-S
are not actually between the engine and the chassis, but
between the engine and the front suspension subframe. This
provides two layers of isolation between engine vibrations
and the chassis: the motor mounts and the subframe mounts.
Hence, adding a torque link from the engine directly to the
chassis would defeat some of this isolation and perhaps
expose the occupants to increased noise and vibration. If
possible, it would be preferable to connect the torque link
to the subframe as well. Or, use really soft bushings on
it.
On to
Cooling
System Upgrades
|