Not trying to brag here, but I run 2 blown Vipers, all IFS/IRS and one is 950 at the wheels at 99 degree outside temp on pump with a conservative tune, the other is 745 on pump. There are plenty of IRS cars that are mean as can be running, Sal Patel is running in the 6 second zone on DRAG RADIALS with IRS in a full weight, street legal Viper GTS. It has AC, passenger seat, radio that works, et cetera. that is not pump gas, but I saw him run a 7.48 2 years back on a track session running our cars with VHT sprayed only on the first 1/8 of the track.

I am a racer too, and not an internet racer with a pretty extensive motor resume building myself. Nearly anything is possible with money and drive, but this seems like a PITA project. I built a totally streetable 491/530 TQ pump gas V-8 that was more than driveable in a 68 GTO, but the cost of doing this to a V-12 would be (more why than anything to me-lol) driveability, expense of parts and engine management. Then once you get that power, you need to do many other things to get it to the ground and the car would not be readily amenable to the power from suspension, brakes, et cetera. If you ran something other than 93, i.e. E85 or higher, that would be a lot easier on an NA build. Me, I'd SC it and anyone wanting to play and needs motors, I have 3 extra V12 jag motors sitting for sale 856-300-5142 from 10-7 M-F Gary

 

Weld to build the journal and regrind

 

Agreed, lifting the head reduces squish etc. I think slight chamber machining and dished pistons (Like Subaru WRX style) would be best as was done in the 5.3 engine this car now has in it.

However this car used a decompression plate in the 6.7L engine. The original engine actually spun a bearing, which is why it was replaced

For Sale: 1977 Jaguar XJS V12 twin-turbo race car - PerformanceDrive


EDIT...... Back on the subject have a look at the dyno sheet this is RWHP while wheel spinning on the rollers. So must be 700+ at the flywheel. This car has also broken 2 Jerico Race boxes, I saw the first one it had a hole in the side of the case.

 

The de-compression plate just increases the length of the bore. I would use a copper head gasket for this instead of a plate as a cost effective solution.

I do not see how this will improve breathing by any significant amount. From what I understand once a valve is lifted to about 22.5% of its diameter there is little to no increase in flow, because the curtain area now meets the valve seat diameter minus the stem diameter.

 

I say go for it James, twin turbos will fit in the bay easier than a SC. I have my cardboard M112 and there is nowhere I can fit the damn thing. DO NOT want dual M90's too complex and additional weight etc etc.

Turn the exhaust manifolds upside down and mount the TC off an adapter plate bolted directly to the manifolds.

I know people say that the valves in the V12 are too small to make power BUT (and I hate to use that word) if you look at a 400hpSBC spinning at 6000rpm with 2.02 intake it has only slightly higher gas velocity as the V12 per cylinder.

Mean Intake Gas Velocity
383 SBC with 2.02 = 248ft/sec
5.3L V12 with 1.63 = 235ft/sec

Now the higher velocity in the SBC would indicate to me that the flow was more restricted than the V12. As port/valve size increases velocity will drop at a given pressure. Fire hose as apposed to garden hose.

 

if it were me, id mock up a centrifugal supercharger to the motor, some can flow enough for 8-900 hp and are only half the size of an equivalent turbo, plus, you're also working on a car thats known for having terrible amounts of heat under the hood.

I have a buddy who has a cf supercharger set up witha clutch engage pully so it idles with no boost, and can cut out on the highway,

cool stuff if you know what you're doing

 

I did not expect this thread to continue like this, but I am a n00b here so let me throw a little into this. Forget about making RWHP and look at the area under the curve for streetability. Judging from the looks, a Whipple twin screw 2.4 liter blower would provide fantastic TQ, but one would have to fab the intake. With no intercooler, use some WM spray, gut the cats, throw some rear O2 sims in and you are off. Go with an AEM for EM and you have a winner. I run a Whipple on one of my rides on an 8 Liter engine and never been beat on the street or track even by guys running 200 RWHP more than me as the HP/TQ is almost linear (also have ported heads, bigger valves, cam, rockers, headers, et cetera). You can do TT's too, but I would fab them in the car and there is room for front or even side mount intercoolers in my XJS at least. I prefer whatever I run to be durable, pump gas only and remember HP sells cars, TQ wins races :-)

 

Agreed, I have looked into this, to the extent I built a cardboard supercharger. The problem is - because the engine is 60deg and the plugs are inside the V there is not enough room to fit it low enough in the V to keep it under the bonnet.

Other things I have looked into are twin turbo, these will definitely fit but the added heat may be undesirable, but still an option.

CF (Vortech or Paxton etc) Supercharger down where the power steering pump is and use an electric pump.

From the research I have done the V12 valves theoretically flow enough for 530hp NA, so this leads me to think that the chamber and/or port shape is the limiting factor. so forcing the mix in should over come some of these limitations.

The V12 has always been a good torquey motor rather than an outright power house.

 

I would personally go with the centrifugal supercharger, possibly on the alternater side if you've removed your air pump, and located the alternator up inside the V.

I think turbos with the lag would really ruin the experience of driving a v12, because I have yet to drive a.turbo car that was smooth and had *****.

not for nothing I think mounting twin m90s wouldn't be too difficult as long as you found a way to get them belt driven. maybe custom vbelt pullys? cut an weld the intake to make them.bolt on the sides

 

AC Compressor is inside the V and we were lucky here in Aus no air pump. I do agree the SFSC needs to go where the PS pump or Alt is located. I think a Toyota MR2 electric PS pump would be the easiest option.

 

My friend the fastest cars on the street are all TT cars now and really if you posted this on a performance forum they guys would be flaming laughing. I'm running a full build Paxton with 10 rib system, 20 fuel injectors, all ported, full Moton suspension and the only thing I am worried about running into are full on TT cars on the street. A Paxton FYI due to setup performs very much like a turbo and can be laggy too if not setup correctly. I'm on other forums and guys own the TT cars, but I also have been in them on the street and with proper setup there can be virtually zero turbo lag. If anyone is really serious about this, I honestly will help you free over the phone, nothing to sell or send you to, but I am a diehard street racer, HP/TQ junkie and also know a guy with a 454 in his XJS locally. I've been in 1500 HP cars on the street and know guys running close to 3000 HP now and spend a lot of time with my cars, other folks and track time under my belt so if needed I can call in reinforcements to help-all car guys why are happy to help each other push the envelope. Anyhow, glad to see you guys thinking put of the box playing around with performance on these cars and I will go back to my n00bie corner where I belong.

 

What does TT mean?

On the Jag v12 and its relevance today: sure, it is much easier and cheaper to do a Detroit V8. But there is a charm that the V12 holds alone. That is why I continue to pursue it, even in the face of obvious logical disconnects with everything else around.

And actually, the Jag V12 can be made to perform rather strongly: the TWR racing efforts in the Group A and Group C and LeMans activities showed that this engine could be developed into a winner. I have an acquaintance who has a set of the Group C heads he tells me that were later banned by the racing sanctioning body for 'excessive noise'. In reality, he says, the TWR Group C cars were dominating Porsche, Ferrari, everyone, and something had to be done...

So, the engine has possibilities.

One thing I read in Allan Scott's book on TWR and the XJS: the flat head engine was thirsty because the required level of turbulence in the combustion chamber was not achieved. The later HE engines achieved this, and fuel consumption improved, although overall performance potential was limited by the new head design. But, TWR was able to regain the turbulence (needed to provide the octane tolerance of the varying quality of fuels available at different race courses) by altering the piston design in several ways: 1) moving the bowl under the plug, 2) creating more squish zone, and 3) enabling the piston to come within 0.040 of the head (instead of 0.150, as Jag settled on). This last created the level of squish and turbulence that enabled the higher CRs they were running (to as much as 12.25:1). The main hurdle to > 10.5:1 (which the factory indicated was the upper limit) was head gasket design. This was also addressed in the TWR engines.

So while I agree the engine is pretty much old-school by today's exotic standards, it still has some surprises to offer.

And, it has 12 cylinders.

-M

 

TT, means twin-turbocharged, viper is right ,in todays world of street performance ,nothing is gonna beat TT.
and the integrity of the engine is the limit!

and i love the Jag V12, because they are cheap,so that says where i'm at, retired and fixed income, playing with the big boys is over!
i'll leave it to guys with almost unlimited income!

most of the guys here know some of my posts, when i was leaving Florida, had to dispose of YES,three jag v12 engines two GM 400 trans, brought them to a junk yard, got $25. each, total of 75 bucks, so thats where the value is in OLD jag parts!! i coulda cried when they put them in a shredding machine.

some day we may see vipers & vetts going that way( that scares me).

and your comment of this site,, guys are internet racers, kinda nails it, i suppose me too.
things would be boring without this site!

 

I think this is a great discussion. I have a 6.0L V12 sitting on a pallet in the shed waiting to be modified. This type of discussion helps to build information.

I have run the 6.0L stats through the Wallace racing calculators and with stock valves this engine should be capable of making 575hp. So the $64,000 question is why is it so hard to get to this in a stock engine?????

Using the same Wallace Calculators (all using 90x78mm Bore Stroke)
Intake port minimum diameter is about 1.34" (according to AJ6) so estimated port velocity at 6500rpm is 627fps well below the 690fps choke point.

Intake Valve diameter HP calculator stock 1.63" inlet valve = 525HP

Inlet valve curtain area = .332" lift = .375 so there is enough lift to minimise valve shrouding and lifting more without chamber mods is useless. If you look at the valve layout in the cylinder there also very little shrouding especially of the intake valve. And the valves are spaced further apart than any chev layout, reducing thermal transfer from exhaust to intake.

So based on these assumptions the 6.0L V12 should be capable making 500hp with very little modification. We all know this not the case with the Jaguar V12.

My hypothesis is the chamber shape is not ideal, there are a lot of edges around the exhaust valve. Maybe this is the cause of the lack of power potential.

I put this out there for comments so feel free to chime with any input, my goal is come up with a plan to modify my 6.0L V12.


EDIT........ I should have said I am not looking for an all out HP machine, what I am wanting is a good strong street motor NA if possible but FI if I can not meet the needs NA

 

Heads, valves and cams will only get you so far. A proper designed intake manifold system is critical too. Using Chevrolet development as analogue....there is an article that details an intake manifold test called "TPI shoot out" from 2005. The tested 10 diffrent intake manifolds on the exact same engine. The difference in HP from the best to worst manifold was 95HP. Same goes for exhaust manifolds.

 

if you can make that much power out of a 6.0 with the he heads, then it should be very capable of the pre he heads seeing as they have the same intake valve size, and less exhaust restriction. plus I have all the ports opened up to be an even size all the way through.

also, I spend a lot of time at the engine shop watching my builder assemble the bottom end, and he explained that CFM is not an.accurate measurrement of flow as because the air will go to and from a dead stop 3000 times a minute at 6000rpm

 

'Why so much trouble with the HE head': power is generally made in the head, and this head was designed for fuel economy. When Jag did the 6L they got the additional torque, but not the HP, in proportion. You get the proportionate HP when you use the flat heads. See the recent book by Allan Scott on TWR's Group A efforts, esp. the later chapter on 'racing improves the breed'- this shows the proof.

Also: the OEM exhaust on the XJS saps most of the HP potential. We all know this is a big restriction. Group A addressed this by using a replacement cast manifold that kept the three cylinders to a downpipe individual, and then going to a carefully tuned pair of twin tubes, dumping to a 3" collector and out. This is very much like the AJ6 TT Extractor setup (except for the cast exhaust manifolds).

It is useful to look at the Group A progress in pulling HP out of this motor. It is useful because Group A required same sized intakes, exhaust, valves, and valve lift. Cam timing was 'free' and so was piston design and CR. The later Group A cars were producing 500 HP under these conditions. But they did so with carefully massaged intake manifolds (in the OEM envelope) and exhausts. They were also running 12.25:1 CR on this flathead, and they were able to do it because they made improvements in the head gaskets and they were using a specialized crown, and a pin height that got the pistons to within 0.040 of the head (and not 0.150 as the stock motors do). This gave much more squish, enabling the higher CR and more octane tolerance (which is how the HE works).

-M

 

I want to take back the comment on pin height- I don't really know what pin height they were running- maybe standard (they were using 5.3 motors). I know pin height is an issue for piston design when fitting flat heads to the 6L block. That's probably how it crept in!

-M

 

im working on doing most of thoes things with my motor! I have a quench height of .050 which is where it should be, except I have higher lift cams ans longer durration with ported and polished heads.

where can one find this book? I want it very badly!

 

do you have ant other information about what they did to the envelopes?