EDIT: update.
The idea currently is to lump the 5.3 for a 6.0 and be happy, or to take an H.E. install flathead pistons, fabricate a twin carbd 4brl manifold, add boost, viola.

 

definately thinking of dropping the injection system and going with a twin carb'd Flathead.

 

First can you let us know what model XJS there were differences in CR and ignition between the years. If your is a HE I would not go replacing the heads with flat if you do you will also need to replace the pistons. The HE heads with some boost are capable of 700+hp with the right engine rebuild.

If it is HE you will need to lower the CR as it will be somewhere between 11 and 12 depending on the year and country sold.

This can be done a number of ways
* Custom pistons - expensive
* a de-compression plate this would have to custom - could be expensive
* machine a dish in the stock pistons
* use off the shelf Holden 202 +0.040 pistons or WRX +1.0mm both will give you 93mm approx so a bore of the cylinders will be required and some machining of the piston.

You could boost a a pre-HE, but without an engine built to take boost you would be limited to about 6psi on a stock engine. Which ever way you go you will need to build an engine capable of handling boost. I am happy to share my research as I have done plenty. I was planning to twin turbo mine but will most likely go with centrifugal supercharger and a capacity increase (bore and stroke) to 6.5L.

I would not ditch the injection - if you are handy there is an ECU called Megasquirt a couple of guys around have used these on Jag V12's along with Ford dual EDIS-6 distibutorless ignition with success and there are reasonably priced.

This guy has a twin turbo XJS and he put it up on the hoist for me have good look over. http://www.jagworks.com.au/

cheers
Warren

 

hey, thanks for the reply. youve got some great info there. i havent bought the car yet. i wanna start off with the most ideal car, instead of buying one and stuggling with it.
so according to you i would be better off boosting a non H.E. v12? and why is it limited to 6psi? is that really all the headgaskets can handle? im assuming this engine, since it is E.F.I. has got a map sensor? if so, can the map sensor understand boost figures?
thanks again.

 

I would go for the latest model you could find preferably an 1989 or later as these engines had the lip seal (rubber) as apposed to the rope seal that leaks although you can have a rope seal crank reground for a lip seal.

Buy one that has no rust if you can find one or a little as possible. Check out this guys web site good info on where and why the XJS rusts. Jaguar XJ-S and XJS (all variants 1975 to 1996)

I would not worry too much about flat or HE heads both can be made to develop power with FI.

I say limited to 6psi due to head gasket and pistons. Boost puts enormous load on pistons rods and crank. The crank is almost bullet proof and the rods are pretty good.

My plan is to have the crank offset ground for Chevy 6.0" H beam rods reducing the BE journal size to chev small journal 2.0" and mating to WRX HPC 93mm pistons. This will lighten the rotating assambly considerablly I estimate by over 1kg. This will give me 6.5L and a reduced CR to 8.5-9.0:1

It does have a MAP sensor but you will need to replace it as it most likely will not accept boost, or very much boost. I don't know as I have not found any specs on it, just replace it they are cheap use one off a local Turbo car.

 

by "local turbo car" you mean any boosted car? ive got several map sensors off my pontiac that will handle boost. i guess i could adapt one for the AJ6.
since im planning on going pre H.E. so i can run as much boost as possible, theoretically i could reduce compression even more by putting may cylinder heads on a flathead block with stock, dished, flathead pistons.
will flathead blocks accept May cylinder heads? im assuming the block didnt change too much for it to not be a simple bolt on.

 

im running 8.5:1 compression pistons in my V6 with 10psi.

 

Correct you can bolt the HE heads to the older block but why use pistons that were not designed to take boost. Use pistons that were designed to run in a turbo car.

You mention the AJ6 this is the I6 engine not the V12

Going pre HE will not allow you to run as much boost as possible - only a proper engine build will let you do this.

Take a look at what this guy did and this car uses HE heads Lyon's Tales -- The On Line Virgina Jaguar Club Newsletter - Page 5

 

I think you might be under estimating what is required to make serious power. It does not matter whether it is a Jag V12 or a BBC if you are going FI the engine must be built to take the enormous pressure.

An engine running 10psi boost and 9.0:1 CR has a effective CR of over 13:1

 

sorry, what is the correct designation for the V12 engine? i was pretty sure it was AJ6.
i dont particularly want to make an engine build out of this, as i can't find parts/bearings/ gaskets/ head bolts/ for the V12.
im guessing the dished pistons from the flathead block arent particularly beefy. so if i went may heads on a flathead block i could run 6psi safely? thats really all the more i want. im dont want to undertake something i cant handle. i wanna start off small and work my way up.
you were talking about your CSC project. do they make a CSC kit for the V12? are you talking procharger? do they even make a turbo kit for the V12? personally when i started planning this project, i was planning on doing an Eaton M90 build using a variation of the M90 that mounts on a bracket and pumps air out the top, similar to the way a turbo or CSC is "set up" so it doesnt have to have a special Intake manifold made for the blower to mount on.

again, can i use pretty much any map sensor capable of boost readings?

also im curious as to what gearbox your planning on putting behind your CSC build, or what your using currently.

 

what do you mean by BBC?
and yes ive read the twin whipple jag article. very wonderful read, but not much tech info.

 

Big Block Chev

I too looked at M90 and Toyota SC14 although to have everything mounted under the bonnet would require using 2 -- one on each bank. There is a guy here in Aus that has mounted 2 SC14's to a V12 said it was a relatively easy mount. 1 M90 would not be big enough to feed the V12 you could use an M112 but would need to stick it up through the bonnet on a custom manifold

There are no kits currently available that I know of so everything will need to be custom.

I decided to go CSC with a capacity increase. I need to replace the pistons anyway so may as well offset grind the crank to 84mm stroke and using chev small journal rods means I don't need to have the crank welded and ground. Chev rods good for 500hp in a V8 will be good for 750hp in a V12 (hp per pot).

Subaru pistons are the right size 93mm is about as much as the V12 can be bored without replacing the liners. If you replace the pistons the liners will have to be honed anyway as the piston and liner are a matched set. The Subie pistons can take 350hp all day in a 4pot (1000hp in a V12) and are very cheap for the HPC (NOT forged). The wrist pin will need to be machined with the rods to fit and the rods machined to fit the crank. But with this done 700hp will be acheivable with reliability.

Here are some pics of a twin turbo V12 here in Sydney

 

haha, sounds like youve got a good machine shop in your area. which is something i dont have.

 

I am currently rebuilding the rear end - almost complete with 4.09 gears and I have a 4L60e to go in.

Next will be a front end rebuild although this will be a partial as I have already replaced the bushes.

All this in preparation for the supercharger. I decided to go the CSC route as this is what Lister did with the 700hp 7.0L twin Albrex supercharged XJS Lister V12, and with the 4.09 rear PDSC would make 1st gear useless.

 

m90's definately arent the best set up. im running 10 psi with a P&P housing and a 3.4" pulley. it generates a lot of heat. pretty much anything will run cooler, but the m90 is hands down the most simple blower for a low budget build.
how is the belt setup on the V12? would you have to have a custom balancer? do they make a harmonic balancer for your motor for blown applications?
my V6 has a dedicated SC belt, so its a dual belt balancer.

 

4l60e is a 4 speed, correct? i have the FWD equivalent in my Grand Prix. im running 2.93's FDR ATM. im very happy with that ratio.

anyone on here tried messing with the 4L80E?

 

M112 would definately not be worth the effort.

 

BTW if you put HE heads with pre HE pistons you will lower the CR to about 6.5:1

 

If you have the Pontiac you probably have the same engine as in my 3.8 M90 V6 Commodore not a bad motor.

Jag used the 4L80 behind the 6.0L V12

Yes the 4L60 is a 4speed but my plan is to put a gearvendors behind it.

The V12 has 4 belts not the best setup and depending on where you are might have an air pump squeezed into the engine bay. There is not much room in the bay

 

Sorry too many posts just reading through

The V12 uses head studs and an open deck wet liner block.

The balancer is there to dampen the crank harmonics so this will only need to be modified if you change the rotating assembly resonance (ie change its weight.)