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E-Type Performance Updates

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The following tech tips were compiled from the member's of e-type Digest from jag-lovers.org. There are no implied guarantees. These suggestions are from other XKE owners on how they solved similar problems or challenges and may illustrate varied and occasionally contradictory conclusions to the same problem. Please forward any questions, comments, criticisms, or suggestions to mhicks@mathe.com. Commercial use is strictly prohibited. Ó Copyright 1998 by Mark Hicks. Legal Restrictions

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PERFORMANCE ENHANCEMENT AND TOOLS

Performance Enhancements

Tools

 

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Performance Enhancements

SUPERCHARGING

We're not talking super performance here, just a little boost, but substantial results. I know someone who supercharged his Jag. Other stock English cars of similar compression mildly overheated with 4 PSI, but I

think that's related to a poorer engine design . Supercharging would net 50% HP increase at 4 PSI for only $3000 including custom mounts, etc. This fellow had no other problems. He also used a vintage supercharger. Todays are more effecient and beat the air less, also some don't need a separate oil line. There are a couple of well known brands which bolt on like an alternator. And.. just what is that empty space where the AC compressor goes good for? 8:1 pistons are better than the 9.1:1 I have, but that means you just adjust for less PSI. Also, most importantly, is some retard control related to boost pressure. The entire idea is not really un-feasable.

 

I am considering supercharging my 72 OTS. 6 PSI would be OK for an occasionally drive stock engine. It is a cost effective way to get 375 HP. This would follow an exhaust upgrade + 26 HP more. I am not really certain of stromberg modifications, which might also be done independently.

 

General

If you want to spend money on the performance do a 5 speed box first lighten the fly wheel at the same time, then work over the suspension.

 

DOHC VS SOHC

The "classical" response has always been that a DOHC system presents the possibility of operating the valves with less reciprocating mass and simplifies the design of the cylinder head. Obviously, one wants a cross flow design to the head - i.e. inlet one side and exhaust the other - and the DOHC system permits the valves to be to either side of the head and operated directly by the cams (in the case of our Jags, via buckets with internal shims).

Of course, cross flow designs are possible with pushrods and SOHC designs, but they are usually compromised by either valve placement, and/or mass of the valve train. If you want high engine speeds, then the valve train is usually the limiting factor as its mass is a limiting factor. The USA NASCAR stock car engines are an interesting example - these highly developed engines struggle to get high RPM due to valve train limitations even with the sophisticated components which are used. They can complete 500 mile races revving to ~8.5k, quite an accomplishment for a pushrod V8).

Ultimately, power is related to engine speed so components and design which will permit high engine speeds are preferable (less reciprocating mass, short stroke engines - our Jags don't do so well in this respect - low internal friction, etc.)

For ultimate performance (e.g. formula 1 - engines revving to ~17k!!!), pneumatic systems replace valve springs - less weight, tendency to float, etc. - but this is beyond "exotic"!

Then, why don't all cars have DOHC - simple, cost. Compare all the "bits" we have with those of a typical pushrod or SOHC engine (the weirdly complex 6 cylinder BMW/Bristol engine and anything with desmo' valves excluded), and you will understand. However, Japanese manufacturers must be complimented in producing small, relatively low cost and superbly made DOCEs which give excellent power with equally good reliability.

Of course, these are only some of the reasons, none of which should bother us, as the two cam covers make the XK engine one of the most beautiful in realistically priced cars (provided one has the early, smooth cam covers - I risk multiple "flames" here from Series II owners....). I am embarrassed to admit that I have spent far too long simply standing and staring at the engines of my early E and XK140, they just look so good!

 

DOHC VS SOHC (2)

Although the low reciprocating mass of DOHC valve trains is often touted as their greatest advantage, that is not quite so. A well designed SOHC valvetrain using rocker arms usually has less mess moving up and down than a DOHC system does.

The biggest advantage of the DOHC engine is the STIFNESS of the valvetrain. With the cam lobe directly depressing a bucket tappet, whihc, in turn, directly depress the valve stem, there is nothing in the system to deflect. No rocker arms to deflect, no pushrods to buckle slightly, no nothing.

This stiffness allows a DOHC engine to use a more agressive cma profile to pop the valves open more quickly and keep them near their fully open position longer. This in turn promotes breathing.

It also makes for a more tractable engine. In a high performance, single cam, pushrod engine, for example, a cam grind with a very long duration is usually needed in order to get the valves open long enough and far enough to breather properly at high revs. Ironically, at low revs, such a design transfers the cam's long duration to the valves more effectively than it does at high revs, which is why such engines tend to have lumpy idles and very little torque at a low revs.

The DOHC engine, on the other hand, due to its stiff vavle train, does not need such long camshaft durations to achieve useful valve openings at high revs. Consequently, it can idle smoothly and pull strongly throughout the rev range.

DOHC designs have another advantage when coupled with four-valve cylinder heads. It allows the spark plug to be placed smack in the center of the combustion chamber, which promotes efficient combustion and reduces the engine's taste for high octane fuel. With an SOHC engine, the camshaft is usually in the middle of the head, precluding this optimal plug location.

DOHC designs do cost more, but their advantages in power and combustion efficiency make them beneficial even for non-sporting cars. Which is why they have become available on Toyota Corollas and Ford Contours.

 

Tools

THE ULTIMATE EMERGENCY TOOLKIT

The following was submitted as a list of items used by a dealer who picked-up and drove various vintage cars from the docks to their dealership. It included a variety of items to cover most emergencies and problems.

 

Contents:

 

2 qts of oil

1/2 gallon of gasoline (I think its illegal to carry gas on a buss now)

1/2 gallon of distilled water

1 qt of ATF (also used in the power steering and carburetors dampers)

1 pint of Brake fluid

2 adjustable length fan belts

1 set of 3/8 inch drive sockets (metric and SAE)

1 set of 1/2 inch drive sockets (metric and SAE)

1 small "crow bar" and a tire tool set with a small sissors jack

1 roll of gasket material

1 can of Permatex gasket sealer

1 tube of GE silocone sealer

1 package of "Bars Leaks"

3-4 stainless hose clamps of different sizes

1 each philips and common head screwdriver

2 vice grip pliers (one large and one small)

1 needle nosed plier

1 oil filter wrench

1 electric air pump

1 set of jumper cables

1 roll of duct tape

1 set of various light bulbs

1 roll of electricians tape

1 set of dealer plates

1 spool of #12 wire. insullated

1 kit of electrical fittings and a crimp tool

3-4 shop towels

1 can of hand cleaner

2 valve stems (interior bits and a valve stem remover)

1 tire patch kit.

1 package of muffler sealer

1 headlight bulb

several & various length and size fuel and vacuum tubing

an assortment of fuses

A magnet to retrieve things

windshield wipers

some cotter pins of various sizes

a flash light (torch for the limeys) with fresh batteries

a plastic "jump suit" that I could zip up over my cloths to work in.

And some Band Aids and iodine!

(To which others added spray lubricant)

 

Most of this list are small things and even though it sounds like alot it all fitted into a medium sized suit case. Most of the room was taken up by the gas and water and other fluids. Leave out the gas and water and you have a very nice size.

 

The kit was mainly designed to get ANY car from the docks to the nearest auto parts store parking lot where I could work on it and get parts. But I NEVER needed to stop (except for gas, they drain the tanks before putting them on the boat) after leaving the docks and just drove straight home.

 

 

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