Doing my research, advice and thoughts wanted

I am in the process of planning out a custom car build. The idea of the build is an “early 60s” Cadillac “concept” for a European style sports car along the lines of a Ferrari 250 GTE/330 GT 2+2, 275 GTS. The car should come in around 3,200 to 3,500 pounds.

I’ve been looking at the BMW M70/M73 and the Jaguar V12. My hopes are for a mild build (around 350hp), in a fairly “sports car” configuration. The engine will be backed by a 5-speed, and the whole thing will sit on a slightly stretched (104" to 108" wheelbase) C2/C3 Corvette frame.

I’m thinking 5.3, but am unsure if I should go HE with early heads, or just a non-HE engine. I’m also looking at ITBs.

I’ll open by simply asking what are your thoughts on the viability of such a Jag V12 build?

Dang, no one has any thoughts. I’ve done a good bit of searching, but most questions of “more power” are geared toward large numbers and not the 350hp range.

Based on what I have found, I’m thinking Kent cams and custom pistons. I would think you could machine a wedge shaped combustion chamber into the pistons, giving good squish without shrouding the valves. I’m hoping to get 11:1 compression, if it feasible, and a 6,500 to 7,000 rpm redline.

Overall, if you are looking for easy, not terribly expensive HP, the way to go is the Chevy LS1 crate engine.

The 12 can be made powerful, but not easily and cheap. Tech-wise, the LS1 eclipses the old-tech V12.

Thanks for the response!

I’m not looking for big HP, only to get a bit more HP than the 300-ish it came with, hence the “350 HP” mark.

For this project, the engine needs to look like it could have come in an early '60s GM Concept Car.

I looked at the BMW 12, but it has no fewer issues then the Jaguar unit (and it’s more expensive) has.

Well, if this is the case go for the Jag !!
At least here there are some really passionate, and more important, knowledgeable people in this forum that will be willing to help you with all your questions.
They know the engine’s shortcomings and have most of the remedies.
And if you rebuild it using modern materials, seals and gaskets you can have a very reliable engine.
All the basic components are bulletproof.

Download the Book if you haven’t done already:

It’s an excellent piece of engineering BTW…!
Good luck.

1 Like

As far as ITB’s I am building my own ITB setup out of BMW K1200 gt motorcycle ITB’s. You can see my build thread if you want, some fun stuff is coming, just waiting for some parts and material. If you are willing to spend a crap ton then this Jenvey kit is pretty good. (

1 Like

Stew Jones builds V-12’s for E-Types, and we use to have Claiborne (sp?) on this site who built a 170mph XJS.

1 Like

You probably are referring to Chadbourn_Bolles. This guy:

He has not posted on JL in awhile though

Try his website.

Whats the diameter of those ITB’s?
Link to the build thread?

If you want to find out the best options for the V12 and spec you want, talk to Rob Beere in the UK.
Rob has been building V12 for years as well as the 6’s so should be able to tell you how to get 350hp.


1 Like

45mm V12 XJ6 Conversion Build

45mm in diameter of the blade? (inner diameter) any particular model of year to look for ?


I believe so. they come from 2006-2008 ish BMW K1200 Bikes here is one of the listings I bought. I only have 8 right now planning on getting the last 4 soon if a set popup for the same price.

1 Like

DriftWorks on youtube used 2 sets of E46 M3 itb’s for his V12 Murcielago. but they have oval ports that are much larger.

The price on the M3 TB are just ridiculous like the Jenway setup…

Ill probably go for the BMW K1200 as the price on a set of tb x 3is really nice and 45mm is enough for me :slight_smile:

Can you measure? What I find on the internet is that they are 38mm inner diameter…

Bill, it’s much easier to make extra HP with the early engine. The HE head has pocketed valves and you can’t go larger.
The early engine can take a1.75in intake valve, 1.63 std. (leave the exhaust std.), and with porting of both intake and exhaust ports you can easily get to 350HP with a mild or even stock Cam.
TRW achieved 450HP+ from the early engine with std. valves with comp cams.

1 Like

I was thinking, looking at the flat-head engines, custom pistons with a tight squish area around the outside and a nice bowl for the combustion chamber, say around 10.5 compression, should do quite well.

Greetings All,

I’d probably go with the Beemer. Easier and cheapervto get horsepower out of it.

Not sure where the tranny will come from likely a T5.