// JagWeb // XJ-S Help // Contents //

 

XJ-S 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 332011 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.

Air Cleaner Housing

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.

Cool Air Intake

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 inch exhaust pipe, but 2-1/2 inch 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 (2-1/2" 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.

JaguarSport XJR Air Intake

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 V-12.

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 !!!

Intake 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 17, 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.

Figure 17 - Butterfly Housing Airflow Improvement

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.

Revised Butterfly Housings

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 K & N 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.

Alternative Inlet Systems

Forget all the above minor modifications and purchase one of the alternative inlet systems made by AJ6 Engineering. One of their systems replaces the cast aluminum intake manifolds with a tuned steel tubing assembly. AJ6 Engineering claims an increase of 55 HP with this kit. All engine accessories, including the air injection system, remain undisturbed.

To present a countering opinion: Bill White, who is an expert on intake systems, reports that the rearmost runners on the AJ6 Engineering manifolds gain a little boost from being at the end of the plenum, and provide cylinders 6A and 6B with a slightly larger charge than the other cylinders. Since all cylinders receive the same amount of fuel, this makes these two cylinders run leaner than the others. If the EFI system is using oxygen sensors, they will pick up the oxygen from the leanest cylinder in each bank and control accordingly, so the rest of the cylinders will simply run slightly rich; no harm done. However, White also reports that, when used with non-feedback EFI systems, these engines tend to be tuned lean to achieve maximum power -- and end up burning the back two pistons.

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 V-12.

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.

Idle Mixture Adjustment

The Electronic Control Unit for the EFI system is in the right side of the trunk, and there is an opening (sometimes covered with a rubber plug) in the side of the ECU. Within this opening is a shaft with one flat side, like those under radio knobs. This shaft turns in little snaps, and adjusts the fuel mixture at idle. It is intended to be adjusted only by the dealer while the car is connected to emissions monitoring equipment. Don't mess with this knob; you'll only end up making your car idle smoother.

To make not messing with this knob easier, you can open the ECU up by removing several screws, then use a hand grinder with a small cutting wheel to cut a screwdriver slot in the head of the shaft. Be sure to get all metal particles out of the works before closing it back up.

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.

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.

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 V-12. Trevor's people have the computer equipment to work out power and 0-60 mph 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 Suspension & Steering Modifications section 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 36000
• GATAbgastechnik, 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, GarmischPartenkirchen +49 (0)8821 1036
• Oettinger, Friedrichsdorf +49 (0)6172 705355
• Walker, Viernheim, +49 (0)6204 7380
• 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 V-12 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.

If you have an XJ-S H.E., Chad Bolles says you can get more performance by replacing the camshafts with the pre-H.E. models. Apparently, the E-type Mk III, early XJ12, and pre-H.E. XJ-S camshafts were all alike, and were "hotter" than the H.E. camshafts. Due to longer duration, the result should be more power at high rpm. Whether the car will still run on 89 octane fuel is uncertain (it probably wouldn't require much higher octane, if at all). The fuel economy would probably suffer a little, since increased duration usually hinders fuel economy at low speed.

Chad Bolles also reports that Isky makes high performance camshafts for the Jaguar V-12 -- hotter than any original Jaguar camshafts.

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.

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" and 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.

Valve Guides

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.

Valve and Seats

The valves and seats on the Jaguar V-12 are supposed to be machined with 44.5º angles. Most machine shops will suggest that the seats be "triple cut", in which additional cuts are made at angles greater and less than 44.5º in order to control the width and location of the contact area. Typical angles for these cuts would be 32º and 60º and the contact area width should be about 1.5 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.

Porting and Polishing

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 V-12, 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.

CC-ing the Head

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.

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 Modifications

The Jaguar V-12 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.

Risks and Benefits

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 U.S. 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 V-12 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 offers 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 White has prepared a Jaguar V-12 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 V-12'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 V-12 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 aluliners 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 pickup process is accelerated and the material wears out quickly. The nickasil was only used on race engines with frequent liner renewal.

Multiple-Valve Heads

There have been experiments to adapt the 4-valve DOHC head from the Jaguar AJ6 engine to the V-12. The bolt patterns are reportedly alike. Since on one side of the engine the intake ports will be on the outside and the exhaust ports will be toward the center, one of the heads must be turned around backwards, and therefore some complicated fabrication work is required.

Steve Averill reports that the Autumn 1988 issue of Jaguar Quarterly has an article on...

...a 60 valve DOHC V-12 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.

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 states. 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.

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 it to original condition for some reason.

I elected to use what automotive electrical rebuilders refer to as a 'large case GM 70 amp alternator with 12 and 6 mounting'. Obviously, this should not have a serpentine belt pulley; a standard GM Vbelt 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 US$30.00 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 integral 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 'down' 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/Cair 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/Cair 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 heatshrink 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 'battery' 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 'hot' when the ignition is on.) Plug in the two main Jag alternator leads to the 'battery' 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.

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.

Crossover Pipe

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.

Mufflers

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.

Catalytic Converters

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.

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 V-12, 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	C31063	C31063
Gasket
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 V-12 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 the Drivetrain Modifications

 

 

---

// JagWeb // XJ-S Help // Contents //