I hope you right about the head flow. As for the intake my feeling is that the plenum is too small and not direct for good flow. In stock form incoming air has to make a 90 degree turn into the throttle, then 1/3 the air has to got left and 1/3 goes right, and then make another 90 degree bend into the runner. That is not ideal in any case. I'd strongly suggest you section and enlarge the plenum for more volume. Then move the throttles to the front edge of the plenum like BMW did on their V12. If you do this the air will have 1/3 the number of 90 degree bends and if you get the plenum large enough they wont matter as much. Since the stock plenums are alu and square, some flat stock welded to a sectioned plenum and a nice plate on the front drilled for a throttle is a serious welding project but very doable.

 

the intake I am looking at is from the group a car, andIt flows 185cfm after extrude honing. u found some head numbers online. stock you're looking at 145cfm, at .4 or .5 lift and after a mild porting it jumped to 185cfm

 

if I build something like that I will.most likely get 3 inch aluminum box tubing and have it welded on the side

 

the funny thing about extrude honing is that ut brings the intake to a.mirror polish, and a roughed up surface does better on the flow bench than a mirror polish

 

Wasn't there a company in the UK called Forward Engineering that was getting big power out of the older V12s? I read about them in the 80s and actually contacted them about dropping one of their engines in an E-Type.

 

stew jones has a couple 7.3 engines.that make over 500bph, maybe the used the same techniques.

 

[QUOTE=dgr8n8;738725I seem to have run into the same thing everyone else has...It is possible but limited success with deep pockets..[/QUOTE]

Next for me is Porsche 928 GTS twin turbo Kuhn kit, or Ferrari 456 with custom twin turbo kit. I feel it's the way to go.

As much fun as a twin turbo XJS would be, I find the 928 and 456 much more modern chassis to experiment on.

It's all talk till it's done, though. :-|

[edit]

to Ronbros and everyone else who has had the stones to significantly modify your XJSs, Cheers. I'm considering a quantum leap.

 

I have talked horse power with Blue Dorward who owns a TWR XJS he built in about 1983 or 84.
At the time he worked for TWR, bought his car new from Jaguar, drove it off the production line and back to TWR where he rebuilt it. He stroked it to 6.4 litres by building up the crank journals then re-machining them with a longer throw. It is essentially Group A specification, 5 speed Getrag, Gp A brakes, etc.
Dyno'ed when built, it had 410 bhp & 405 lb-ft, he claims it can do 175mph.

I said it must be fun to drive, he said I can have a drive sometime, I said what's it like, he said You'll f***** **** yourself...

 

im actually in the process of buildind a 6.5 stroker motor, the car has the journals machined for sbc rods using chevy 6 cylinder bearings custom forged pistons and 278 duration 440 lift cams! and hopefully group A intakes aswell! its already got a Bw t5 five speed with heavy duty gears aswell

 

Take a look at this:
Lyon's Tales -- The On Line Virgina Jaguar Club Newsletter - Page 5

 

That's an interesting conversation. Allan Scott, in his TWR XJS book (Group A history) tells of the path they were on in Group A. Couldn't reach 500 HP until late in the Group A effort, and this was the result of much intake and exhaust manifold work (constrained by Group A rules) and a lot of cam work (Group A meant valve sizes had to be OEM, and lift OEM, but they found a way to bend the rule a bit on that one).

The engine development work undertaken for Group C is much more interesting, and here's where they were expanding displacements. They had a 6.4L motor (same bore, longer stroke), 10:5:1 cams, and this was making a really broad torque of >400 ft-lbs, and >400HP. I don't think this same result is easily possible on an HE, although Chad Bolles may disagree.

-Mike

 

There are a couple of 6.0L engines here in Aus making 450hp. I think with advancements in engine management over the past few years it is possible to make 500hp from a NA V12. Although I think FI would be cheaper and easier.

 

So, here is my question: Do you have to drop compression for a twin turbo setup like you do for superchargers?

 

Good question. I am interested in the answer because...

I picked up a very low mileage 1979 pre-HE motor, in order to pull the heads, and locate a 6L block. Then, planned to bore to 92 mm and build from there. But looking at the costs involved (custom pistons, etc.), it then became obvious to me that I really should look at turbocharging instead. Power potential is much higher, costs about the same or less, depending on how its done.

Here's why: the 1979 motor I have is set up with 7.9:1 pistons. I figure set the engine management up (replace injectors) to run E85. This should get us into the 450 HP range without too much trouble. On a 4200 lb XJS, this is just starting to enter the territory where the car will get interesting to drive.

The main concern I have is drivability- I want a good streetable motor. So low end behavior and lag issues are on my mind. On that, I found a couple of guys who use very short nitrous bursts run by the engine management system, done at low rpms, to provide the exhaust gas hit required to spool the turbos more quickly. With tuning (the $10,000 question), it is said to provide a pretty seamless power curve. And, sipping at the nitrous bottle makes the supply last quite a while (the nitrous is on less than a second or so).

So, optimizing CR for turbocharging: a better CR for this motor out there?

-M

 

I think I can answer some of these questions.

First of all, CR and turbo engines do have some relationship. The idea is that a lower CR will allow you to run more boost and thus ultimately produce more HP. However, it is a game of diminishing returns. At some point, for each .1 that you drop the CR, you will not be able to run enough boost to make it up. I think you guys already know this. It holds true for supercharged and turbo engines.

There is a flip side to this: as you drop CR, you will make your engine feel more sluggish out of boost. Throttle response will not be as crisp, and it will not have the pep that you want driving it around town. I built my non-Jag engine for FI at 8.5 CR and it was a bit of a dog. I bumped it up to about 9.5 with a new set of heads and there was a very noticeable difference. The bottom line is that you probably want a happy medium. Things like a good intercooler setup or meth injection will help you keep your CR up while still being able to run the boost that you want. IMHO, getting the CR right is a key part of drivability.

One note - different engine designs act differently with CR numbers. The engine I took from 8.5 to 9.5 was an LS1. Just because my LS1 felt sluggish at 8.5 does not mean that you V12 will, etc.

Regarding the nitrous system - it sounds like a crutch to me. With over 5L of displacement and a properly sized turbo, lag should not be an issue for you. A larger turbo will typically produce more ultimate power but will come on later in the power band and have more lag. A smaller turbo will typically produce less ultimate power but will come on earlier in the power band and have less lag. Most people want something in the middle.

There are other things you can do to alleviate turbo lag. If the car is a manual, you can usually downshift. Higher RPMs seem to get a turbo pulled much much faster. If the car is an automatic, a looser torque converter will help get you into the power band sooner.

 

But with most of the HE motors the CR runs around 11:1. Could 2 small turbos running a lower boost still work without blowing the head gaskets?

 

I think this depends on a number of factors.

1 Fuel will need to be high octane
2 Detonation will need to be controlled - low boost, ignition timing and you could use water meth injection to keep the intake cool.


Lowering CR to 9.5 to 10:1 would be better. There are turbo kits here in Aus for stock LS1 engines running 10:1 and making good power. Lowering CR could be done with a thicker head gasket or decompression plate..

 

the OPs question is; has anyone on this site actually made 500hp, well i ask, is that at the flywheel(BHP) or measured at the rear wheels (RWHP)??

lots of good advice from many,but seems its all speculation so far, so its back to the OP ques. who,if any has done any serious mods to there engine?

transmission and gearing comes little later,after the horses are let out!

jags original R&D said that for the pre-he heads C/R was around 10.6 max with premium fuel for that era. engine durability was in question after that,for a street automobile!

decomp plates requier two head sealing sides,one top one bottom, expensive!

thick gaskets could work, more money,.
both methods lose the important squish and swirl of the combustion process, MPO, is a custom piston, with a proper shape,
,now think slowly here<< when you raise the cylinder head away from the bore, you lose some of the effective valve lift,valve does not go down into the bore far enough, for effective breathing and flow.

remember we are trying to get more air into the cylinder not the chamber or even the piston bowl!!

a mod i did on my engine puts my valves .050 thou. deeper into the cylinder bore, my cams only lift the valve .400 thou. but my machining work puts the valves(effectivly) .450 thou. further into the bore. old hot rod idea, the great thing about an american hot rodder, is they do things because no one ever told them it wont work!! hehe.

 

Ahhh...BUT, with forced air either by turbo, supercharger, etc.. you can overcome some of that intake restriction/obstruction. The resistance is still there, but the air is forced past it to a degree.

It does not help with evacuation of the cylinder exhaust gases, but I'm not sure how much of an issue that may be.

I have a spare 5.3 with 56,000 miles on it. If I don't sell it I may look into what it would take to put twin low boost turbos on it. I'd probably just build an engine stand to make it easier to work on and worry about putting it into a car later.

 

if you get a chance could you ask him how he got an 84mm stroke on a stock crank? id be much abliged (: