More power for the V-12 Engine

I was cleaning out some old files on my computer when I came across an incomplete document that I had long forgotten.

It was titled “More HP from the V-12” and was intended to be an additional link on my website. (This question has again resurfaced)

As most of you know I no longer own my XJ-S and as such have a minor, intermittent presence on the Jag-Lovers list.

That said I have decided to update this information and post it as the last final link to my website.

For those interested it’s titled “More Power for the V-12” and can be accessed at the following URL.

Fair disclaimer, these are my opinions only. (smile)


Bad start, Bernard. The Jaguar V12 debuted earlier than that in the SIII E-Type and had carbs.

…the V12 in its fuel injected form debuted in 1975.


Should have made that clear. I was of course referring to the fuel injected models. Will update link to clarify (smile)

Updated website to clarify that this link only applies to the fuel injected models starting in 1975.

thanks Bernie, pretty much how modded mine 25yrs ago!!

BASIC GOOD engine knowledge, what American Hot Rodders have been doing for close to 100yrs!

and Allen Scott also said Torque is King especially on the street, stroke it as much as your pocket book will allow!
what a lot of guys dont know, is the Jaguar V12 was engineered for Smooth ,Quiet , driving , when engineering changed from the V12 4 cam Hemi design ,to 2 valve single cam , power was NOT considered important!
your papers are spot on tho!
stroke it and GEAR it!

Wouldn’t a change to a 700R4 GM transmission provide the lower first gear with an overdrive top gear be a prudent improvement?

Dave that is what i have , been since 1994, Corvette 700R4 , and 3.73 rear ratio LSD!

best mod for the cost, and ratio in overdrive is 2.60 final! best of both worlds!wild%20cat%2Cburnout%20006 !

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“Wouldn’t a change to a 700R4 GM transmission provide the lower first gear with an overdrive top gear be a prudent improvement?”

Absolutely!! Imagine cruising at 2000RPM rather than 3000rpm!!!

I fitted a 4L60e (later version of 700R4) to my Jensen Interceptor (3.07 diff) and that car is a fantastic cruiser. Interesting though, on this car, I’ve programmed the transmission to pull away in 2nd. With that 440ci (7.2L) torque factory, 1st is excessive. I can not only access 1st manually via gear lever. Never do it though.

Fitted a 700R4 to my '70 Chev C10 truck with a 350 V8. Likewise, good pull-away, but delightful at cruising.

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HI Jagwit, i had a Camaro with BBC , it to was almost usless in 1st, so reprogramed the trans for 2nd gear starts ,AT LIGHT THROTTLE< But when pushed past 3/4 throttle it kicked down into 1st, and car started sliding all over the street, and tire smoke everywhere.LOL!
actually would lose forward traction and become slower!
it became a different driving experience!

after that ,when building my V12 5.3L Jag , i found V12 does not have a lot of torque,as most people think they do, they have a long flat torque curve , the torque they do have lasts longer and more RPM!
BUT sometimes you have already lost the race to a V8 car, so give some thought when modifing !