When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Easiest - ZZ502 BBC Marine motor-
Hardest - v12 with 6 webers - tuner's nightmare?
The TH400 isn't bulletproof and costs approx. 50 HP loss due to rotating mass. I have lost the 1-2 governor which was an easy fix. It is the best 3 speed GM trans built. I would love a 60LE OD trans but not worth the effort.
Hot Rodders love the GM400 & Jag rear and we see some $100k+ rods with them here in AZ.
those in pix are for show,not for GO, a solid rear axle is best for hard straight line acceleration, and if you are not lifting the front wheels ,you dont have enough tire grip or torque!
and for myself i'd use a GM 4L80E trans much stronger than 60E. there is avaliable a 6 speed shift kit for the 80E.
I don't like swaps in Jags myself but there are limited options:
- LS swap & 6 speed has been done here.
Back to orig topic:
The HE or pre HEs need CNC head work or port & polish, EFI tune and bigger injectors to get anywhere near those numbers. a Full rebuild of a Jag v12 is $6-12K. Not as bad as a MB v12 but pretty steep.
I don't like swaps in Jags myself but there are limited options:
- LS swap & 6 speed has been done here.
Back to orig topic:
The HE or pre HEs need CNC head work or port & polish, EFI tune and bigger injectors to get anywhere near those numbers. a Full rebuild of a Jag v12 is $6-12K. Not as bad as a MB v12 but pretty steep.
it would take a lot more than head work and injectors to make an HE or pre HE, get to 500hp!
the ones that make big HP are always after big cubic displacement.
at least a 1/2" stroker,and as big a bore you can afford money for!
7L plus.
and for some odd reason, real XJ-XJS Jaguar enthusiests want 12 cylinders(i know i do)! V8s-V6s just dont compute,there are in-line 6 guys, but they are NOT after serious HP.
Yes a lot of head work.
I have a pair "pre HE" that were prepared in England to TWR spec they have large ports and valves. I am aiming for 7.3 Litre.
I have a cross ram throttle body injection system with long intakes, and injectors just after the throttle bodies. "Will post pictures when I get time"
An Emerald programmable ECU already set up for a TWR 6.0L so will need tweaking.
I have a big bore liner set that will have custom Arias pistons and Megacycle cams to Bill Terry specs.
A similar set up in my E type race car gave 385 BHP @ 6000 they are now touching 400 with the six.
On a recent trip back I saw a 7.3 that had been dynoed @560BHP but they had to stop due to an oil tank issue. The tuner says there's more!
I wanted to build an XJS race car as I am getting bigger and need more room.
I owned my first in 1981 when I lived in England and am building a 1976 now.
Now this will have steel main caps crower rods and a dry sump and lots of trick bits so is not a practical road car.
But it does have a Florida title so will be driven on the road occasionally.
At the end of the day it is not about the HP its about owning a V12 Jag.
I bloody luv em.
Unfortunately the V12 heads and intake are a severe compromise. The ports are all wrong for high rpm flow, and that's what a super short stroke, stock displacement Jaguar V12 needs to make horsepower.
If there was a market for more than about 10-20 units, new heads and a modern barrel type intake would resolve the issues. Until then, the only solution is to bandaid the heads and add displacement.
It's interesting, but for all the "sophistication" that is attributed to the Jaguar V12, the valve layout is much more of a compromise than many "primitive" pushrod V8 engines.
Jaguar really should've separated either the intake or exhaust valves from under the cams to allow a proper valve angle for better flow. It would've also allowed much better port layout. Even a 15-20 degree separation in valve angles would've allowed much improvement in breathing and valve sizes.
Of course, that would've meant also moving the distributor to a more sensible position, like on the end of the camshafts and Jaguar was too constrained by a lack of development money to do that.
Yes a lot of head work.
I have a pair "pre HE" that were prepared in England to TWR spec they have large ports and valves. I am aiming for 7.3 Litre.
I have a cross ram throttle body injection system with long intakes, and injectors just after the throttle bodies. "Will post pictures when I get time"
An Emerald programmable ECU already set up for a TWR 6.0L so will need tweaking.
I have a big bore liner set that will have custom Arias pistons and Megacycle cams to Bill Terry specs.
A similar set up in my E type race car gave 385 BHP @ 6000 they are now touching 400 with the six.
On a recent trip back I saw a 7.3 that had been dynoed @560BHP but they had to stop due to an oil tank issue. The tuner says there's more!
I wanted to build an XJS race car as I am getting bigger and need more room.
I owned my first in 1981 when I lived in England and am building a 1976 now.
Now this will have steel main caps crower rods and a dry sump and lots of trick bits so is not a practical road car.
But it does have a Florida title so will be driven on the road occasionally.
At the end of the day it is not about the HP its about owning a V12 Jag.
I bloody luv em.
I live in Florida also ... but the LA part...
would love to see your car when it is done...
and Please post the dyno-sheet when you are done... (or better a nice link to a video of your dyno-run)
I am sure it will impress...
I just got the radiator in and am very happy...
just got one more leak to fix then I will dyno mine in stock configuration...
and yes it is about owning a V12... Jaguar... (or aston martin V12...)
Last edited by Jonathan-W; 10-15-2015 at 09:48 AM.
i agree 44L, the Jaguar IRS was never ever designed for a good drag acceleration launch, with tires that hook to the track!
race Group44, 1977,1st change for racing was a complete redesign of the IRS!
i have seen 1st hand of the whole sub frame ripped loose and be catty-woompas sidewise, needless to say the race day was over!
The IRS and diff are good for anything you can chuck at them; I did however find the limit, with 600 PF of torque from a big engine on the drag strip at Santa Pod. I heated the rear tyres by burning them on water before the staging area to get them nice and sticky,
as the christmas tree light went down I dumped the clutch at 4500 rpm and there was a bang as the car lurched forward and twitched, a tad off putting but I kept my foot in and completed the run for best time of the day by a Jaguar.
Got my cup and was happy.
It was 2 months later doing a sprint event when I found out what the bang was all about, when I went onto the grass and tried to restart I found only 1 rear wheel was spinning, bemused by this lack of traction I checked the diff and found that one of the output stubs had twisted and sheared, the previously straight splines and twisted to about 45 degs before the output had let go. This was all easily cured with a replacement output stub and simply not dumping the clutch again with sticky tyres, they were 14" wide by the way.
Finally got my TWR inlet castings from Bob Tilley of V12 Sales. they are at my local foundry now and I will have the 1st test manifold next week.
These are the original V12 TWR Group A manifolds made to allow the V12 to breath and to produce just over 600Bhp
Diameter of the finger runners at the head is 35mm
Diameter of the runners as they reach and blend into the plenums is 45mm (just a little larger than the OD of your standard manifolds.)
I tried to get hold of a pair of these babies when I raced XJS's in the mid 80's but never got close to getting them or even finding someone who would admit they existed. Only 6 pairs were made in period and I believe 3 pairs have been made since. The Foundry owners tell me it would cost close to £100K to get this tooling made nowadays, the main core box tooling is machined from billet aluminum and weights over 40kgs on its own!
If you want a pair let me know Looking at 2-3 months until shipping a deposit will be required.
This could be a 1 off as its outside of what we are concentrating on at the moment so dont hang about. Happy to answer any questions.
If you dont know what these inlets are don't worry about it. If you go hunting for hens teeth you are likely to get more success.
Finally got my TWR inlet castings from Bob Tilley of V12 Sales. they are at my local foundry now and I will have the 1st test manifold next week.
These are the original V12 TWR Group A manifolds made to allow the V12 to breath and to produce just over 600Bhp
Diameter of the finger runners at the head is 35mm
Diameter of the runners as they reach and blend into the plenums is 45mm (just a little larger than the OD of your standard manifolds.)
I tried to get hold of a pair of these babies when I raced XJS's in the mid 80's but never got close to getting them or even finding someone who would admit they existed. Only 6 pairs were made in period and I believe 3 pairs have been made since. The Foundry owners tell me it would cost close to £100K to get this tooling made nowadays, the main core box tooling is machined from billet aluminum and weights over 40kgs on its own!
If you want a pair let me know Looking at 2-3 months until shipping a deposit will be required.
This could be a 1 off as its outside of what we are concentrating on at the moment so dont hang about. Happy to answer any questions.
If you dont know what these inlets are don't worry about it. If you go hunting for hens teeth you are likely to get more success.
SO, are you taking orders? for a run of these... ?
are the plenum volume any larger than stock factory? the tapered runners look great(I LIKE). air flow must speed up when it enters the bowl area, to give extra swirl into the chamber, lately some guys are adding a small ramp in the runner/bowl to introduce some socalled tumble(hoping to add more in chamber turbulence) in a quiescent chamber! do you have some pix of the piston you plan on using????
nice stuff , TWR near the end of there developments, must have been way ahead of the rest of XJS racers! quest; did grp 44 ever get any of these types of modifications??
maybe of interest;
i had my inlet manifolds/plenums EXTRUDE HONED, very nice work, took out all humps and bumps internally, opened all runners and plenums about an 1/8", along with a fairly smooth internal finish, opened the TBS 1/4" tapered slightly!
how much it helps,DONNO, but cant hurt for increased air flow , heads ported/bowls and smoothed ,oversize valves, tulipped/ lightened and polished.
head surface cut to valve seat level .050, that way valve goes deeper into cyl. bore, when open(kinda like more valve lift) .
that was back 20+yrs ago, 5.3L still runs fine, but back then a stock 6.0L crank was around 3K US with shipping!
come to find 6L crank is not a drop in for a 1978 block anyway.
and like 5006 says 84MM,or more, stroke is the best way to go for more power, its all about the torque!
When I raced XJS's and couldn't get a sniff of these Group A TWR manifolds; the best we could do was to spend a small fortune on long shafted burrs flex drives and flap wheels and check what we were doing with discs tack welded to rods. In the end we band sawed the plenums to get decent access to the entrance to the finger runners and blend them open to the max, Took about 2 weeks work to do each manifold and we hogged them out so much that you didn't dare lean on them. Putting the outside of the plenum back was easy using the triangular end plates. Tried adding (tigging) material to the underside of the fingers to allow even more opening but the distortion junked the manifolds. What I ended up with was vastly superior to standard but still nowhere as good as these manifolds.
Here are the pistons that work with the plenums, I have no intention of re inventing the wheel. Bowl in piston for pre HE and valve cut outs only for HE.
These may be the last set of genuine Cosworth Group A pistons left.
And yes if anyone wants the manifolds drop me a line
these are XJR=s or XJR15 (very Similar) again Cosworth.
nice pix of piston , i'm guessing the top pix is for pre HE, top piston cast ally,, and two bottom pix are for HE only! (no bowl). forged 2016 ally ?
ron says thanks
I looked at all options for intake that I could get under an XJS bonnet/hood
and came up with these"see pictures" Clever design that will breath.
I had to make my own air plenums and have 4' air intake to each bank through
K&N filters.
This is an ongoing project that changes as I go.
Looks like the Jenvey set up I posted on here 2 1/2 years ago when I saw them at the Autosport show; They look great but having chatted to the guys there I was told that is all they do, they were commissioned to make a set and for clearance under the hood. The crossovers had to be too severe and the runners ended too early to allow the throttle bodies to fit with hood clearance.
Still a nice looking bit of kit. I guess if you could fit wedges between the heads and runners to raise the manifolds and extend the runners putting the throttle bodies the other side of the cam covers then they might work better but from memory the ID was too small , was it 32mm at the head.
They are 35.2 1.385" at the head with enough material to go bigger and 46mm 1.811" at the throttle body. And a tract of 201mm 7.913.
Two V12 engine builders seem to think they will work.
I will know when I get to the dyno.
And they had to fit under the bonnet.
No power bulge other than that of a six cylinder XJS.
That's good news, I can only guess that Jenvey modified the tooling when they got sufficient interest. I still think they should have extended the runners over the cam covers for greater length but hey thats a great improvement on the prototype.
Originally Posted by PGV12
They are 35.2 1.385" at the head with enough material to go bigger and 46mm 1.811" at the throttle body. And a tract of 201mm 7.913.
Two V12 engine builders seem to think they will work.
I will know when I get to the dyno.
And they had to fit under the bonnet.
No power bulge other than that of a six cylinder XJS.
That's good news, I can only guess that Jenvey modified the tooling when they got sufficient interest. I still think they should have extended the runners over the cam covers for greater length but hey thats a great improvement on the prototype.
I think so.
I know what you mean by the tract length but when you add the throttle body length to butterfly and reverse bell mouth its quite good.
Also my F1 buddy says the placement of the injector so far from the valve will improve things.
High end that is.
if you are going to manufacture new cylinder heads , then i would put the injector exactly where it should be(in the combustion chamber,direct injection)!
go big or go home.
also my opinion, multi TBs, are far more tuning problems than two large single TB.
but they do look kool, but so doesn't a supercharger/turbo system!
i have said this before, a modern 4cylinder turbo engine can make great performance/power, and much lighter weight, probably 400lbs less weight over the front wheels. just dont brag about your engine,LOL.
but if pure power and great fuel MPG where important,
my dream choice would still be a AUDI V12 diesel,comes from factory with twin turbochargers, direct injection, light weight(compared to Jag V12)etc.
without taking engine apart, just reprogram computer, redo piping with large intercoolers, use a built GM 4L80E with 6 speed kit!
i'm betting 30mpg would be possible.
now the important part,, 650hp, 800lbs ft.at 1900 rpm, carried to 4000rpm ,would make a great street vehicle, 4000rpm in overdrive,with 2.88 rear would come around 150 mph, but passing accel. would be staggering at 40-120mph!
10-13-2015, 11:11 AM
