[QUOTE=Forcedair1;847553]The SL 600 v-12 is CA compliant and the car was registered in CA.
The car is in Scottsdale now and I believe I have seen it at shows.
There is more money than smarts over in Scottsdale!

The aj16 is an easier motor for mods like forced air and N20 as there is a much simpler design and much more SPACE!

I bought Nitrous Express Wet N2O for my '89 XJ-S v12. It proved to be a PITA to tune and distribute even flow to each cylinder. The N2O broke lots of parts at the track and a Ford TBird was a better candidate.

 

Sir Lyons bet the factory on the V12’s and shortly after the Suez canal was embargoed driving up fuel costs. Following that California proposed ( and implemented) tough new smog laws. Without the more than 50% of sales California represents Jaguar was out of business.
So instead of a steady power development, there was a frantic search for smog compliance and better fuel mileage. Following the lead of Chevies powerball cylinder head, the HE was created and forever cursed power production.
Gross horsepower of the 60’s& 70’s was not anywhere near net or DIN horsepower rating. A Chevy 350 horsepower V8 turned into 160 hp net. About 150 DIN when Jaguar was at 242 . By 1975 with Corvette still at 160 hp Jaguar had gained 20 more horsepower to 262 and in the non smog world wound up at 299. DIN. !!!!!!!!!!
Joining BMHL, in order to survive his poor return Sir Lyons simply was out of money.
Not just Jaguar but all manufactures struggled through the 80’s, only Fords investment in the 90’s saved Jaguar.

Admire Mercedes and BMW but their v12’s Had to comply with the same smog rules. And reflect it with similar horsepower output. Yes lighter chassis and a few manual transmissions but don’t forget that Jaguar offered manual gearboxes too at first.

Yes BMW & Mercedes-Benz developed twin turbo’s while Jaguar was barely hanging on.

 

Why not just leave it in the Audi?

 

Full conversion to Diesel with a VGT turbo. I think the baseline is there, the bottom end of the V12 is solid, with some better head studs it can probably handle pressure and a slight uptick in compression ratio.

My 6.0L v8 diesel cranks out 600hp and 1100lbft of torque on mostly stock parts, no reason why a well maintained V12 couldn't get within ballpark range of that. No need for twin turbos either just one big truck unit.

 

MG the Audi V12 diesel twin turbo/twin intercoolers , direct injection etc, was only available in the BIG 6000lb, SUV!

being as XJS is much lighter , it would make a Formidable road car!
ron

 

If you like the Mercedes please go ahead . It’s a world more complex. reportedly 3 separate computers. But who can argue with the power? Same with the BMW. I haven’t followed them except for a few friends who report them to be just as complex and expensive to work on.
Because of their complexity mechanics are just as eager to take advantage of the typical owners ignorance and sell unneeded maintenance.

 

Please do not spend the money for Weber’s. They shorten the intake tract too dramatically and absolutely kill the bottom end. Not to mention the hood is just above the carbs. Thus forcing intake air to make 2 sharp right hand corners to get into the carbs. That just kills flow!
In addition Weber’s do not come tuned for Jaguars, you will wind up spending a lot of serious money buying jets, air correction meters etc. going on the Dyno to get closer, ordering more etc. Now-days few if any Dyno operators know how to make Weber’s really right for the application. Not to mention the variability of air density. Depending on what the weather was doing I changed settings 2&3 times a day

 

There are so many plug & play transplants with $25k being the limiting factors. The Hell at crate motors are finding old Mopars and other classics. Pricing on exotic engines is really the lifting factor. Some rebuilt v12s are not avail for $25k, the cheapest rebuilt v12 jag is $8-12k using Jag factory parts.

 

If you want a modern engine what are you doing here? The earliest Jaguar V12 designs date from the late 1950’s by 1963 they had a 500 hp V12 in the works that wound up in the XJ 13.
Jaguar bought Coventry Climax in the early 1960’s and got two state of the art engineers who focused on turning get into something suitable for big sedans.
As was Jaguars tradition they first released it in their sports car ( the XKE ) then moving it into sedans.
The mid 1970’s & 80’s dealing with new pollution laws it still was a powerhouse making more than 100 horsepower than the small block Chevy.
From the Mid 80’s GM’s deeper pockets allowed it to develop fuel injection and electronic ignition into greater and greater reliability and power, eventually catching up in power and surpassing Jaguar in reliability.
Both the small block Chevy and the V12 stopped production about the same time.
If you want Modern Jaguar still has the DOHC4valve V8 with optional supercharger. That compares very favorably with the Corvette motor for power and reliability. Although like the pushrod rocker arm Chevy V8 that too is getting very long in the tooth

 

I had a nice reply nearly finished when Chrome decided to eat it. Here's the short version:

Money no object: Buy a Ferrari 550 Maranello.

$25k answer: Keep the HE V12. Getrag 265 swap. 3.54 rear end. Exhaust improvements. Big throttle bodies and ECU retune. See V12Gents on Youtube for a model of what I'd like to do.

Current plan: Tune the TH400 to the point of being tolerable. Fix the stuff I know is wrong and do a bunch of catch-up maintenance. Then see about the items from the 25k answer.