Well i have driven dual clutch MB GTS and Audi s6 both 4.0biturbos and both really powerful cars so i know what is dual clutch tranny capable of, but still good old full manual behind v12 is really fun to drive for me.
approximately i know how your car is performing, i own also SIII sedan (same weight as XJS cabrio) with pre H.E, 10.5 compression engine with enlarged throttles and MB auto tranny, it shifts exactly at 6500rpm and you can hear wheel spin sound at each shift.

 

this car weighs in at 3475lbs.

weight 3475 lbs ,,1/2 tank fuel,

engine , 355 Wheel HP! dyno.

 

I think you are intentionally missing the point.

But's that's OK; never mind the whole thing. Forget I ever said anything

This s wayyyyy more trouble than it is worth.

I had a hunch this might happen. I should have followed my gut feelings early on and just not said anything. Monumentally poor judgement on my part. There's no fool like an old fool, as the saying goes

Carry on; I won't pester you again

Cheers
DD

 

Great beast!
What mods been done to engine?
And where about 400 lbs have gone? fiber panels?

 

I’m familiar with the T 56 it’s a double over drive gearbox with relatively broad spacing between gears. nice piece for street use and capable of dealing with a great amount of torque.
A Seinz is a 5 speed non overdrive. So very close ratios. Like a Hewland it’s for serious racing only. It’s also a Quick gear set change Gearbox. You pull the back plate off like a Halibrand or Winters quick change rear end and slide the gears out and slide a new set right back in. In the pits transmission still in the car you can do it in 15 minutes.
on the bench if you want you could probably do it in 5 minutes or less.
The original owner couldn’t get used to shifting without touching the clutch and used to go through a complete gear set in a single session.
When he gave it to me a long time ago I never needed new gear sets. Throttle flat to the floor the faster you move the lever the less the dog gears wore. Down shift required you to mat the throttle as you moved the lever.

I’m familiar with double clutching and matching RPM for the old straight cut gears on Tractors , trucks, even MG T series, Jaguars( until 1964), etc. ( I’ve raced them all )
A dog ring is nothing like that at all.

 

Mates, GREAT POSTS and I am delighted to see posts like this in 2018 to present, not all stopping around 2008.
I have picked up a 1988 XJS 5.3L V12 Th400 for a long term project. Supposedly 80k miles but seems in much worse condition. Motor seems OK.
I picked up, around Jan 2019, a 1996 VdP with about 200k, ended up replacing AJ16 and ZF 4HP24 . Just now getting use of the VdP.
I see so much life, what a surprise, in the V12 so late after end of production that I am most pleased.
So glad to see all this tremendous info. Best regards, Rob in rural Arizona.

 

Great to see the specifics, especially the LT1 transmission which seems the better choice down the line. Is there a post on changing out a TH400 to a TM56 for an 93-97 LT1? Thanks!

 

So I weighed my '88 today. Heading into the Carson City Landfill with a full tank of fuel, two gallons of waste motor oil in the boot, along with a 5lb fire extinguisher and my fat *** (about 175 in street clothes), the scale said 4080 lbs. After dumping said motor oil, the outgoing scale kept switching between 4060 and 4040. I'd call that 4050. Accounting for driver weight and the fire extinguisher, I get a curb weight of 3,870. Car is stock except for having the center mufflers deleted and I have a few interior panels and speakers out of it right now. It also popped a new exhaust leak today, so I no longer have to complain about it being too quiet. However, it's not loud in a good way. One more thing for the to do list.

 

I’m going by what was available. In 1972 a LT1 Corvette was something like 350 hp. But by 1976 that Corvette 350 cu in was rated at 160
yes changes were made. But I doubt you’ll find a LT1 in. A junkyard. Or available as a crate engine.
Yes a 450 hp 454 is different than A 235 go 454 but again finding a 450 Hp 454 isn’t going to happen in a junkyard or as a crate engine from the factory.

To to be fair the XKE NEVER HAD 265 horsepower at the rear wheels. Not in the 3.8 version or the 4.2.
If it did they were ponies with really short legs. I had some pretty highly modified engines on the dyno and 210 was the most I ever saw. The XKE series 3 with the V12 always was listed as DIN net. So 242 DIN ( 235.3 SAE net horsepower.)

The sad thing is the numbers of used 307 cu in engines with chrome dress up kits installed and sold as rebuilt 350’s then they’d pull the turbo 400 for the turbo 350 transmission . All because they didn’t understand that electronic Fuel injection was actually easier than carburetors.
Now that the system is better known. And there is a really good 3 part series on U tube. To explain everything. It shouldn’t happen.

Listen, I’ve been a lifelong Chevy owner. They are great. But if you want to race one you’ll need to replace nearly everything. I raced Corvettes and Chevy powered sports cars for decades. I know what is required. To be competitive in one nearly every part needed to be scrapped except the Block. NASCAR eventually did that.

 

OK the V12 makes more horsepower and Torque than a Chevy 454. I know you’re confused but the difference is between the old Gross or Advertised horsepower and New Net horsepower. For example a 1970 454 might be advertized as 435 hp but a 1974 454 would have a net SAE horsepower of 230 hp.

Jaguar has 262. Net DiN horsepower So the V12 makes 32 more horsepower than a V12. DIN horsepower is just a tiny bit more powerful than SAE.
Easy power increases? Take off the air cleaner housing*. That chokes the engine down 30 net horsepower. The mufflers used cost 20 horsepower over a less restrictive muffler design.

Unlike a V8, headers do very little for a V12 over the stock cast Iron manifolds. And they weigh only 4 pounds each.So there is no real weight savings either.
Easy real horsepower? Replace the stock injectors with ones 30% bigger and start using E85
that’s going to net you about 35 horsepower
Changing cams on one of these can be done in less than 1/2 the time a V8 requires. But cams shift the power curve higher in the rev range. You will gain 80 horsepower with a set of Isky XM3’s but at 7,000 rpm not out of the hole.
A manual transmission is an easy swap. The alignment dowels line up the gear box. All you need to do is make a adapter a simple mornings work with a drill press.

 

Nonsence. The year is 1990. A Jaguar XJS and Chevy 1500 SS pickup with 454 line up for a drag race. The Chevy gets to the traps in 15.9 Seconds, the Jag 16.4. Both use Chevy's TH400 transmision. If you put that BBC in the wind cheating body of a XJS instead of a rolling brick good things would happen. Clearly the BB has more torque, and the XJS has perhaps (,maybe). The trap speed of 87 vs 95 for the Jag tells the story, might be the same HP if you consider aerodynamics

Complete nonsence. I've done tests with the intake and exhaust like you described on a well tuned 6.0. Then, I evaluated their real world performance using a Gtech pro. The times suggest very modest gains. I recall something like 10 combined. Zero chance it would be 50 HP combined. You have ZERO evidence this is the case.

Partial Non-sence. Headers really come into their own when the the cam overlap increases but even an stock engine can benefit from a well designed header. It's fairly well understood that V12's need 3 - into 2 into 1 headers just like a inline 6 only doubled side to side. That's three primary into two LONG Secondaries. Then the 2 primary's into a collector. Like all headers we know this would make more torque, becasue it does so on inline 6 engines and a V12 is just two inline 6's. I tried to do with on a XJS in the past with a T56. For me there just wasnt enough room for two long secondaries on each side with the header making skills I had at the time. I may try again with a TXK 5 speed, they are much more compact. The length of those secondary's is critical and it's how BMW got more torque and HP from their V12 with less displacement. Jag did this on the AJ16, they stacked the two long exhaust secondary's top and bottom on the passenger side. I'd love to see how they did this on right hand drive cars. Must be tight with the rack tower in the way

I like the cam regrind idea and it's my understanding ISKY still offers this service. The V12 flat lines at 5200 or so, would be nice to have the power carry another 1000 RPM and get the torque lost back with the long secondary. Not so sure that would net 80 HP alone.

 

first. Look it up yourself. Check the difference between gross and net horsepower.
Second at 4600 pounds the XJS is not meant to drag race.
Third the top speed of a Jaguar XJS is 150 mph. Yes several magazine sets confirm it will do that speed Stock, your Chevy?
The temps under the hood are so high Jaguar had to put a fan on the battery to keep from melting lead. In addition the factory had to air condition the fuel line to keep from boiling the fuel.
That hot air ain’t good for power is it? Now look at the air cleaner on the 5.3 Tiny opening spread out to about 3 inches at the filter.
open that up and according to AJ6 engineering that’s worth 30 horsepower. AJ 6 is owned by a former Jaguar engineer and no they don’t sell fresh air intakes.
Headers are needed in a V8 and can make a major improvement. That’s because of the uneven firing order. Adjacent cylinders can be fired between 90 & 270 degrees A V12 has an even 60 degrees firing Order. One cylinder pulsing then the next pulsing and the third pulsing. An even 120 between each cylinder.
Now forget what nonsense you think you know about tri Y headers. You need to stuff about 27 feet of tubing in the engine compartment. Equal length headers. That is what Grouo 44 used on their headers ( and me ) the formula to use is available on most header design programs. If you do everything exactly right you will gain 4% more power for your troubles.
All out racers find it worth it. But look at the sheets, that 4% you pick up is in the get-a-Ticket area. Want to know how much work it is ? Go to U Tube and check out Camp Chaos Chronicles. By Robert Knodt.
Isky does offer several regrinds. But so will almost any cam grinder. If you choose to go that route, weld up the lobes so you don’t need to go through the exercise of adjusting the shims. A side note. Bruce Crower of Crower cams San Diego helped Group 44 find more and more power with the V12. If you are looking for 6-700+ horsepower that’s who you talk to. For street cams Piper and Kent Cams in England are actually better but the import duty and shipping make them a very expensive choice.

 

i aint gonna touch this BS!
MG can go on forever!
been there done that, on JAGLOVERS!

 

Wait, what? Was that before or after they put it in the boot? I don't remember seeing any fan back there... nor do I have any melted lead.

 

Yes . but on the 6 and 12 sedans.

 

I'll buy that... but I'm on the XJS forum, right?

I'm just trying to learn how to help my XJS work well. The HE had a purpose, no surprise it's not "optimal" for a build. I'm so confused. It doesn't help that the above seems to be comparing a 326 cubic inch engine with a 454 cubic inch engine. And it's not like a Chevy Big Block doesn't get hot. Any '67 Vette driver can tell you that! I guess I'm not understanding the discussion here.

 

There's just a lot of mis information on this thread. I don't see how denying reality's is constructive. No meaningful way to move forward under false pretenses.

 

I wouldn't say the HE wasn't optimal, for it's time it was a very powerful engine, and like most engines it has things it does well and some not so well.

A major difference is that Jaguar has already unlocked most of the potential, so there is not much left that can be done. I am assuming a street engine in a road driven XJS, all out race engines are entirely different design goals and compromises.

 

My Chevy's... Lol, I own an L92 Powered Escalade and LS2 powered GTO. Both very capable cars with vastly different purposes. No big block powered bricks under my care at the moment.

Actually AJ6 engeneering does sell intake items... (See here) So they have a financial incentive to suggest there are gains to be had. On an otherwise stock engine, the gains are there but very minimal. I evaluated some upgrades for a customer. I found no meaningful real-world intake restrictions on a 6.0. I never did test the 5.3 air boxes.... they do have a rather thin trumpet opening and I can imagine bigger gains can be had by lopping off the trumpets and extending the intakes with some larger tubing flexible tubing. Someone need to test that. Wont be me as I don't go near 5.3's. With the 3 speed, tight converter, propensity to drop valves.... they are just cruisers.


School is in session.... Tri-Y is a Ford / Chevy V8 thing / 4 cylinder import thing. The term TRI-Y comes from a type of header that is popular with some Fords and import 4's that makes 3 Y's. Never a term used for I6 or V12. This type of header is more popular on Fords than Chevy's becasue the ford firing order favors the design. For use on a Chevy one of the primary have to be crossed over to prevent 5 and 7 firing adjacency...so then packaging in a chassis very difficult. IF you use a 4/7 swap cam on a SBC then no cross over is needed and fabricating headers is much easier to package in a chassis since 5 and 7 no longer fire back to back. I know nothing about the 4 banger import uses but I suspect the same issues apply.







All in-line 6 and by extension V12's can benefit from 3-2-1 headers. As show below. From road car to race car. 3-2-1's work becasue of pulse tuning. The fact is that on a I6 or V12 you get a pulse every 60 degrees so separating them is even more importance than on a v8 which has more time between pulses at any given RPM.

 

please learn what the difference is between gross and net power numbers are.
No those engines did not make 400 real horsepower as installed in cars.
Once they were required to measure horsepower as installed suddenly a Chevy 350 make 160 horsepower. A Chevy 454 made 230 horsepower