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My recent BMW V12 engine transplant... [Cobra replica with V12 twin-turbo]

25K views 29 replies 28 participants last post by  Prototype 
#1 ·
Greetings... I haven't visited the board in a couple years now -- I used to own an '03 E39 M5, which I have long since sold. I also own a replica of the Ford / Shelby Cobra, which killed an engine through oil starvation a year or so ago. It got me thinking back to this old post (where, incidentally, someone I've never heard of made some silly comments about kit assembly...):
http://www.m5board.com/vbulletin/e39-m5-e52-z8-discussion/123007-m5-cobra-pics.html

My favorite part of my old M5 -- naturally -- was the engine. So I bought another of BMW's well-known engines and set to work cramming it into a Cobra replica like our forum friend M5Cobra did. There was no M7 or M8, though, so I had to improvise and fabricate a bit...

The result is a twin-turbo V12 Cobra replica making 495hp and 580lb-ft of torque at the wheels. Assuming 15% drivetrain loss, that means I am seeing about 576hp and 683lb-ft at the crank. Boost is currently limited to under 11psi (intercooled). The M70 block and rotating assembly can supposedly take 15-16psi, but the 10mm torque-to-yield head bolts are the weak/limiting factor. Given that I can currently spin 315/35/17 drag radials in the first three gears, I'm not really searching for any more power at the moment. I am running this through a new-old-stock Getrag BMW 850CSi 6-speed gearbox and a 2.73:1 rear-end.

I realize this is off-topic, but this is the most logical place to share, and I figured a few of you would enjoy seeing a random application of a good BMW engine. Read more and see pics here:
Unveiled: Top Secret UBERCOBRA- New Vids pg 4 - FFCobra.com - Factory Five Racing Discussion Forum

Thanks for looking. Motor on.
Cheers, John
 
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#4 ·
Wow. Congratulations on all the hard work finally paying off! Enjoy!
 
#7 ·
Nice work! I'm a DukeGrad also.('92)
 
#10 ·
Sweet car and awesome project. Too bad you're a Duke fan :hihi:
In all seriousness, that is an amazing project!
 
#11 ·
fantastic! Thanks for sharing.
 
#13 · (Edited)
A V12 has long been available on the top-end 7-series (older 750 models, current 760 models) and 8-series (850 model) cars. They were high-priced machines new, and it follows that they were fairly low production numbers. There is no real demand for those engines used, so whenever one is totalled, you can pick up the engine for peanuts. The long block I started with was only $500! I've also thought about picking up a used Benz V12 for a project, but they seem to retain a lot more value than the BMW units, and are more expensive even out of totaled parts cars. Plus, the aluminum intake manifolds on the M70/M73 are just works of engine art.

Thanks for the compliments, guys. A lot of time, planning, effort, and of course money went into the project. I'm proud of her -- but mostly, I sure enjoy driving her.

Cheers, John
 
#22 ·
That is so cool. Congrats on being able to pull this off. My neighbor as a kid tried to build one of those as a kit car and failed miserably - lost a ton of $ and his wife still bugs him about it to this day. Oh well...at least she's still with him! LOL!
 
#24 · (Edited)
Speechless. With the little weight of that chassis, it must really haul as*. I wish you would have turbo'd a BMW V8, I could use the info/knowledge. Thanks for sharing such an awesome project.
 
#26 ·
The twin turbos are all custom work, not a package or kit -- go read more on the ffcobra.com thread link I posted at the top of this thread. The turbos are Garrett ball bearing units, oil fed of course. I used the BMW exhaust manifolds that bolt to the block, but everything from there is custom pipe. Likewise, the intake was custom built from aluminum. Intercooler is a pretty standard aftermarket part, etc.

I don't know of any "kit" to slap a twin turbo on one of these engines, but if you have good fabrication skills, it's not impossible. Also prepare for computer work, because you will need larger fuel injectors to support the boost -- I went with 42lb, and I think the factory ones were only 13lb or 17lb.

For the gentleman interested in building a V8 turbo application, it really wouldn't be any different as far as putting it together. Just look at the engine internals and what they can handle, look at your fuel injector capacities, compression ratio so you don't overboost and detonate your block in half...and then the hardest part -- figuring out how to weld it all together so it still fits under the hood. I had (well, made) a lot more space in my tube chassis than you're going to have in an OEM car.

Thanks for keeping the thread alive --
Cheers, John
 
#28 ·
Nice work with the BMW V12. My question is what bell housing did you get to mate the Getrag up to? Did you just buy all NOS parts or did you have to do some fabricating? I would like more detail from the flywheel to the shifter is you could help me. Could you put me in touch with any BMW knowledgeable folks? I hope to install a BMW V12 in a Jaguar E-type.
 
#29 ·
Smart combo,,,,

but the M70 can take more force than you can imagine,,, 1.2 bar is the limit due the headgaskets,, but a Norwegian guy is boosting 2 bar on stock 10:1 CR ,, 5.4 bottom,,,,,,,,, and making 1400 bhp and 1150 lbs ,, thats somekind of power,, these V12 engines are unreal strong,,, so whatever you blow,, it will hold, but a simple solution to get more boost is Studs, in the head ,, and other gaskets (( dont know were to find a special M70 gasket)) but afaik the M50 studs can be used
 
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