Hi fellow jag lovers...

Hopefully this time tomorrow I should be the proud owner of a Jaguar XJS H.E and I am wanting to turn it into a replica of the TWR Jag that won at bathurst in 1985.
My plans for it would be
Manual conversion using the Gearbox from a BMW M3
grafting the brakes from a modern Supercharged Jaguar with the help of a 3D printer
17" compomotive TH wheels
TFT dash
F type seats
removal of the +2 seats
If you're still with me then I would like to know how I could get to 400hp and maybe even beyond that?
Would it be possible to stroke the v12 using chevy parts?
I'd like to use kent ultimate road cams or something like that as well as porting and polishing the heads and adding a less restrictive exhaust with an emerald k6+ ecu, where do you think that would get me?
Installing the diff out of a 4.0 xjs for better acceleration

 

Please open your wallet and provide us with a metric AND imperial measurement of it's depth, upon review you will be informed as to how much more you'll be spending.

lol but if this is the experience your aiming for you'll be tens of thousands in before getting there, thats if your rebuilding a race engine yourself like some guys here are/have done.

 

Probably the first thing you should do is pick up a copy of " TWR and Jaguar's XJS" by Allan Scott. It details much of the modifications that went into the TWR cars in the 80's.

Next question: is this to be a road legal car, or a pure track car? That will determine the extent of the modification you can do, and if you'll be able to get insurance. Depending on what you want to do and how it will be driven will answer some of your questions. But as mentioned above, the extent of the modifications you're proposing will be very expensive, even if you can do most of the labour yourself.

Alarm bells went off in my mind when you talked about making brake modifications with a 3D printer. Most 3D printed materials are very weak, and will also not withstand braking temperatures. They are actually designed to melt easily, and that's the opposite of what you want in a braking environment

 

Hello Sam

Bathurst - 1985, what a year - my introduction to the XJS.

Since it is a Australian race - this is also a Australian machine going around still


So is possible, if your wallet is big enough

Cheers
Steve

 

Sorry - couldn't resist

5 minutes, 30 in, can't get more aussie than that

https://curiousjag.com/blog/that-yellow-jag-from-orange

https://curiousjag.com/blog/mark-hammonds-xjs/

 

Power,
the problem with the HE heads is the valves are recessed. That means the air and fuel flowing in has to make relatively sharp turns both going in and going back out. that limits horsepower to the 400-450 range at a maximum.
if you can find a pair of V12 heads from 1971-1980 the potential is so much greater. 750 is available if you spend as much as getting 400-450. With the HE heads.
The early heads bolt right on and everything works. I’ve picked up early heads from rusty sedans for very little so don’t give up easy.
The most expensive problem is pistons. Forged high compression pistons will cost about $130 each. Times 12 and go up from there. The best pistons are made by Cosworth, they are not only the lightest but also have the most suitable combustion chamber. In the past I’ve heard of low cost Cast pistons From various cars used, but they need to be modified to either accept the Jaguar wrist pin or used in conjunction with Chevy rods that are modified. All that machine work starts driving costs up.
The stock connecting rods work and can be lightened with a home made jig and a drill press. Pretty easy work
Better are Modified Aftermarket Chevy connecting rods which work in combination with offset grinding of your crankshaft. Thus you wind up with as much as a .400 stroke increase and a bore increase.

The trouble is the stock oil pump isn’t big enough so now you’re fitting a 6.0 oil pump and boring oil passageways etc to correct the plumbing problem Jaguar has.

All those changes Can get horribly expensive. You can spend $ 20,000+!just to get all the stuff you need. And still have to assemble and test it.
Mind you We haven’t mentioned the fuel injection yet!! Stock won’t work!!

Can we discuss practical, affordable cheap modifications? Again the best heads are the early ones. 71-80 in conjunction with the early pistons. But use the later engine blocks 1981-1992. Yes the pistons and heads will work. No you don’t need new pistons. Wear on V12’s is really minimal. Even if the car has gone well over 100,000 miles it’s not uncommon to still see original hone marks in the cylinder walls only rarely are bearings worn excessively. As long as oil was kept up the timing chains can often be reused!! The guides and tensioner will guide you in that regard.
Use the early distributor. 1980 or newer. And here’s the secret to cheap power. Carburetors! The stock manifold with a simple modification will make more power than the fuel injection. Forget Weber’s!!!! Too expensive And no clearance.
Not to mention buying jets air correction meters etc. will cost a fortune and then you need to sort them on a chassis Dyno. Oh, they are wonderful eye candy. Just expensive and no real power gain over a slightly modified stock set up.
Strombergs or SU’s. The Strombergs are 1&3/4 inch compared to SU’s HD8’s which are 2 inch. It’s easier to modify the SU’s than the Strombergs and the SU’s are capable of make a little more power but the Strombergs are much shorter and with the required modification you’re close to sticking the carbs up through the bonnet.

You can easily build an early engine to make 450 horsepower for a few thousand dollars while anHE to make that sort of power is going to run north of $5000

I haven’t talked about camshafts or porting. But those will be required. There are easy ways and hard ways on both of those.

 



 

I was under the impression that 400hp wouldn't be unobtainable if I was replacing the gm autobox with a manual gearbox, upgraded heads, cams, upgraded intake manifiold and a modern ECU.

 

Thank you for the detailed response. 450hp for a few thousand is much better than spending tens of thousands..
450hp would be very nice, indeed. Would you know what the ballpark figure would be for the torque?
So i'll be on the lookout for a pre HE engine from now ow since fuel consumption isn't much of a worry for what will most likely be a weekend car

 

Are the later 5.3 blocks superior to the early PRE HE ones? and if so what is the difference?
thanks

 

the 6.0L engine is far better than 5.3L, many FORD engineered modifications!

 

Oh its very possible, even just lifting the needless dead weight off the car and doing better cold air intake/exhaust setup can free up a fair bit of power, all the emissions junk and the Fred Flinstone era ac compressor is probably 60 pounds at least. I'm just (jokingly) saying it'll be a pricey adventure but again quite possible with deeper pockets.

I asked the guys who own the red & white xjs in the video I linked to they didn't really do all that much it has race cams better valve springs, intake manifolds enlarged (within stock housing) bigger valves to account for that and some light forged pistons, that engine is at about 5.4L but he states the 6L is a better starting point if building a race car.

 

Absolutely agree, but not all of those changes were Ford designed. They needed additional money to implement them but I’m sure they were in the works.
The stroke had long been planned for. You can see it in the design.
The oil pump was a by product of selling to Germans The stock oiling system works backwards. Oil going to the cooler is bypassed oil (except on German bound cars.)
The improvements in the fuel injection though clearly reflect Fords thinking along with elimination of the distributor.

 

Let’s be clear. The pre HE blocks are virtually the same as all the later blocks. About Mid 1977 Jaguar switched from the Borg Warner transmission to the GM Turbo 400 when they did they used the GM locating pins that makes swapping in a Manual gearbox unbelievably easy. You can buy junkyard Or new Manual transmissions T5’s T56 etc and almost bolt them on directly. , Almost but it’s a simple almost. If you can drill holes and cut aluminum you can do it in a few hours.

Rereading an earlier posting, I may have confused you. You cannot use pistons from an HE engine with the Flathead or early preHE heads. You can put the early (used) pistons from the Flathead ( or Pre HE ) in a HE block.
Did that make sense? HE pistons with HE heads Flathead pistons with Flathead heads. Flatheads are what the Pre HE engines 1971-1980 are called.
The best Flathead pistons are in 1980 cars. But only worth a few extra horsepower.

Now with regard fuel injection. Nobody has a easily adjusted system for Jaguar V12’s AJ6 comes reasonably close but it’s based on pretty standardized stuff. if you change cam shafts for example you have to send it back.

Mega Squirt sells a unit cheap but I’ve watched guys spend years trying to get the system to perform as well as the stock system does.
There are aftermarket people who will spend thousands of dollars and give you a plug and play system.

However there are cheaper ways to make power.
Nope, Weber’s while wonderful eye candy Barely make stock horsepower. The air inlets are too close to the hood( bonnet ) and not long enough. Plus just the parts to get them properly tuned will set you back a lot! Not to mention the knowledge and dyno time required.

Group 44 made 450 horsepower in their XKE V12 using the stock( ish) carb manifolds and 4 HD 8 SU carbs.
Huffaker used Strombergs and made more power. Both group 44 and Huffaker agreed they had more power while Group 44 handled better. However the Strombergs are a little harder to tune than SU’s
The Jaguar factory used carbs from 1971-1974 Ask and I’ll give you the details required to make more power with carbs than the fuel injection system has. ( stock the fuel injection makes 22 more horsepower. )
No the fuel injection system will get slightly better fuel mileage.

 

Street driver or race car? If a street driver how much comfort are you willing to sacrifice for performance. And where are you located?
If you are in England/Europe/ Australia some of my advice won’t work for street use. ( that’s a real pity since E85 works even better there)
If in America parts of the country have E85 in many gas stations. While other parts not so much.
With regard to Torque. Even highly modified V12’s have plenty of torque. The advantage of the V12 configuration over a V8. (More details available)
plus even the most wild camshafts idle smoothly. With regard to valve springs. The factory springs were tested by the factory all the way to 8300 RPM before valve float began. So assuming your springs are good that is money saved. There is a poor boy approach to checking the valve springs.

 

I'm planning on replacing the water pump with an electric one so hopefully that should free up some power

 

I'm in England so no e85 for me unfortunately.
I'm planning on replacing the superbly comfortable seats with some electric recaro bucket seats from something a little more modern or with f type seats so it wont be much of a cruiser when I'm done with it

 

no, fortunately I understood that in would need both pre he pistons and heads
I'm in the UK so most of the T5 gearboxes come from cosworths and t56s are hard to find although the occasional one does come up, usually from a vanquish...
would you happen to know what a junkyard t56 would cost?
I was really wanting to use a modern efi system but if it's not worth it then carbs it is.

 

I found a third of the race on youtube and watching the v12 jag dance around the track was intoxicating lol

 

Mguar, I'd be grateful if you could impart what seems to be a treasure trove of knowledge on how to make more power with carbs