BMW V12 Project

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"Supra" Moderator
Staff member
Houston, TX
This is the early stage of the next project, which is trying to shoehorn a 6 litre V12 motor into a scratch built GT40 replica (for you young pups, the GT40 was an American (OK, designed & built in the UK) racecar that won Le Mans multiple times back in the 60's. This car was originally designed for the 4.7 litre small block Ford V8 engine, which was one of the most compact American V8's ever made).

The V12 motor in the pic is a 5.4l BMW model M73, and the transaxle is a Porsche G50.

This is not the actual motor I'm using for the project, but is a "dummy" that we're using just for mock up and test fitting. This motor has no innards, so it's much easier to handle. The tranny is the actual tranny that we'll be using, however. The real motor is at an engine builder's facility and is being gone through completely and rebuilt as a hot street setup. When it's done, there won't be many visual similarities between it and this dummy other than they'll both have six plugs per side!

We're going to sleeve the block then over bore and stroke it out to somewhere around 5.8-6.0 litres, raising the compression to 10:1 or possibly as high as 12:1, depending on the fuel I can get, changing the cams, head porting, etc. For those of you doing V8 buildups, if you think building a V8 is expensive, just multiply your worst nightmare by 1.5 :shock:

Also, if anyone thinks the 1UZ's heads have the worst configuration for good flow they've ever seen, I invite you to look at this BMW motor. It sets a new low for high flowing head design, however it's obvious that was never BMW's intention for this motor. With the nearly perfect inherent balance of the V12, coupled with 1.5 times more power pulses per engine cycle than a V8, it was the best combination for silky smooth low rpm power in their luxo-barge 750's and 850's.

Now, getting this from being your grandmother's luxocruiser motor into something that Enzo would have been proud of will be the challenge.

The cars in the background are a friend's GT40 replica, and a TR6 under restoration.
what are the specifics on the engine? heat reflecting on the pistons, heads, intake? and friction? oil shedding? cam specs, piston specs, rod specs? origional intake? ITBs?

GT40s are cool, but i would go with an Ultima GTR or Can Am instead. fastest street cars in the world.
Can't seem to get the pic attached to the original post. Trying to attach it to a reply post.

Re: the GTR, different strokes I guess; IMO that's one of the ugliest cars on the road, and the Can Am isn't much better. I don't care how fast it goes, it's still ugly - again, only my opinion.

I'll put together another reply later with all the specs of the build; I just wanted to get this one frigging pic uploaded, but am having a devil of a time doing it.
I want to see how this build goes. That's one of the ultimate cars to build as far as I'm concerned. Interesting choice of motor but it sounds like you are having it built to be a screamer. I'm just curious about the weighting of the car with that engine as opposed to Fords race configuration specs. Interesting indeed!
I'm attaching (hopefully) a little comparison table of the Ford motors vs the BMW.

As you can see, it's somewhat longer and taller than the SBF, but actually smaller than the BBF. Unfortunately, I've found, since I made this table, that the dimensions of the Fords that I was given were not that accurate, and the BMW is a fair bit longer than the SBF.

Looking at the weights you can see the SBF was a very lightweight motor at between 440 and 460lbs, however the big BMW motor is only 80-100 lbs heavier, thanks to its all aluminum construction. The BBF was a real pig at more than 200 lbs heavier than the SBF, due mainly to its big cast iron heads, which are nearly 120-150lbs apiece.

It's no wonder the later MKII GT40's with the 427 motors were so much heavier than than the earlier MKI's with the 289's and 302's. That and Ford mandated full rollcages for them, whereas the earliest cars had none!

So bottom line, I'm hoping the weight/handling of the car will not be adversely affected. Perhaps it will even be improved as the engine will be extending further forward than the V8 was, which should help the weight distribution.

Our biggest problem currently is with the height of this motor, as it's a 60 degree V12, instead of a 90 degree V8, plus it has OHC's, where the Ford motors, of course, were cam in block. Getting this thing in without changing the "silhouette" of the car is the challenge. Running the Porsche transaxle inverted as shown, helps a lot because it allows a lower engine mounting configuration than other transaxles, however there's no getting around the fact that it's one tall motor. We'll be drysumping the motor to save some additional space.

One good thing, when it's time to do the classic GT40 "bundle of snakes" exhaust, we'll be thankful it's a 60 degree V instead of a 90. Fitting 12 primaries in a space that was tough for only 8 would be a real PITA otherwise.
very cool project, i love gt40's


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i don't know how far your into and how much you plan to spend on the BMW v-12, but what about getting a stock ferrari v-12, like a maranello 550 engine. Already built and screams and no custom modifing the engine. I wonder how the costs would compare, modding that BMW must cost a ton.
I had actually looked into buying an exotic motor, however they fetch pretty exotic prices. The cost of admission for a V12 Ferrari motor runs around $15K to $20K in unknown condition. Assuming worst case, $25K in genuine parts and Italian speaking labor later, you have a pretty nice motor with a prancing horse pedigree.

My (2) BMW motors cost me less than $1200 total, DELIVERED. I'll put $15 or $20K into one of them, and will know what I have when I'm finished. The reason they're so cheap is because they had a terrible reputation for reliability, however I think it was primarily due to their owners.

How many BMW owners do you know that can even open the hoods (bonnets) of their own cars? My brain surgeon neighbor next door has a very nice midnight blue 740, but has no idea whether he has a V8 or a six under his hood. Matter of fact, I'm not sure he understands or even cares what the difference is. He just knows it's a classic car and it's "correct" for his profession and station in life.

Anyway, that's why I'm into these BMW motors, instead of something more exotic.
BMW did the owners of these engines a dis-service when they treated it as 2 six cylinder engines.

To save money BMW ran it with 2 ECU's so they could use their stock 6 cylinder gear on the engine.

Because of this they have a propensity toward self immolation.

Essentially a good engine let down by lousy electronics.

The concept behind the engine is a little like the UZ family. They wanted smootheness at the expense of outright horsepower.
BMW shops call this the $1000 motor. When the car comes in for service (any service!) it's a $1000 bill. When it leaves the owner on the side of the road, it's a $1000 service call. When the owners have finally had enough of the problems, the motors rarely sell for over $1000.

As Rod said, BMW did a disservice to their owners with the 2 x six cylinder Motronic EMS systems to run the engine. Interesting concept, but a maintenance nightmare. Too, the drive by wire throttles and third ECU to control them, and keep the banks balanced were way ahead of their time, and of course cost at least $1000 to fix/repair/replace. Why BMW implemented advanced technology such as drive by wire, then turned around and did batch injection, and kept the HT distributors is a mystery.

Then there's the intake manifold isolators that start leaking, and the engine has to be pulled to change them, etc. Ka-ching, at least $1000.

Also, the engineering lash-up that BMW called their cam lubrication system, which is simply a copper tube (think normal copper plumbing) spray bar that sprays/drips oil on the camshafts. One loose banjo bolt on this and the engine eats a camshaft. Yep, you guessed it... $1000.

Finally there's the propensity of this motor to overheat and blow head gaskets, then hydrolock and break rods when coolant gets into the cylinders. This is usually when the motor and/or the whole car goes onto eBay.

The two engines I purchased have evidence of all the above problems. But, despite all this, there's still some wonderful German engineering in them, if you look hard enough :boggled:

I'm addressing all the above shortcomings with (hopefully) better engineering, and/or simpler technology:

ECU will probably be a single MoTeC M800

The leak-prone intake manifold spacers/isolators will be eliminated, and the throttles will be ITB's, mechanically actuated, of course.

The cam lubrication system will be improved, strengthened, and pressure sensors added to it.

The cooling system will be improved and better head gaskets will be used (of a similar design to those that fixed the BHG problem with the MKIII Supra).

About finding pieces and parts:

The stroker crank is coming out of the 2nd motor (the "dummy" hanging in that pic). This crank will increase the stroke from 75mm to 79mm.

The block will be overbored to accept cast iron sleeves, then the sleeves finish bored to 86mm. This is being done to eliminate the need for specialised pistons to mate with the Alusil lining in the cylinders.

Pistons will be custom forged Wiseco's, with oil retentive coatings on the skirts, and probably heat reflecting/insulating coatings on the crowns. We're planning on setting compression between 10:1 and 12:1 compression, depending on the fuel I decide to run.

Cams will probably be from the German manufacturer Schrick. Timing will be 264 degrees on both intake & exhaust sides, and valve lift will be 11mm. If I can find better profiles and lifts than this I'll use them. Can't go with regrinds on this motor - too much at stake.

The rest of the valve train, including seats & guides will probably be made for this motor, as they were for my 1UZ project.

On the lower end, the bearings will be ACL or Clevite (same thing) and ARP hardware throughout. They'll get an oil retentive polymer coating, similar to the pistons.

Haven't decided whether to replace the rods or not, or just strengthen & stress relieve them with shot peening and cryo, then use ARP hardware. Probably by the time we get done with all this, it would be just as cheap to replace them. I'll be setting the rev limiter to 7500 RPM, so it won't be "quite" as stressed as one of those prancing horse motors.

The dry sump lubrication system is yet to be engineered and sourced. There will also be a prelube system for this motor like the one on my Supra.

I'm considering eliminating the OEM engine driven water pump and putting in 1-2 electric pumps. It has been suggested by knowledgeable BMW technicians that the OEM water pump gave only marginal performance when new. Unfortunately the main volute of the OEM pump is machined into the block itself, so over time, when there is corrosion or erosion in this area, the attendant loss of metal causes the pump's already marginal performance to diminish even further. Electric pumps have now reached a level of reliability that I think will be suitable for this application, plus they offer more possibilities for better flow control than an engine driven pump. Also, I really like the idea of being able to run the pumps after shutting down the engine, to give it a better cooldown and minimise thermal shock to the motor.
wow cribbj, well thought out. You have very good engineering answers to the problems that are known. My question is, why would you want to start with such a handicapped engine. Is it for the challenge or is that you want 12 cylinders? I mean there are plenty of v-8 alternatives that will make the power reliably and less expensive (ls1, cobra supercharged v-8). Just wondering why this particular engine you have picked for the project (just seems like a massive amount of work/money), i'm not knocking it, its very cool, just curious.
It's just the allure and uniqueness of owning/building/driving a V12 powered car. I've always been fascinated with them from the time I heard a Formula1 Ferrari fire up back in the 60's. When I worked at Cat and Cooper, invariably my favorite motors were the G398, G3412, and the 12SGT, and all these were V12's. Both companies had V16's but they just didn't trip my trigger like the V12's.

The Toyota V12 would have been my first choice for this project, but they're so incredibly rare that they never made onto my radar screen.

There were Jag V12's to consider, but they're heavy pigs, and have a weird head design, and an even poorer reputation for reliability than the BMW motor.

Mercedes built a very nice aluminum DOHC V12, but you don't see them for sale that often.

The "real" exotic motors I didn't consider at all. Nor did I consider any of the domestic V8's or V10's. Shoot, everybody and their dog has a SBC/SBF powered "something", and I wanted this to be unique. For a time, I considered putting my SC'd 1UZ motor in this car, but in the end I decided I really wanted to do it with the V12, keep it NA and have those 12 gorgeous intake trumpets exposed and right behind my head.
Here is a handy shot showing the difference in the oil pans between the newer generation M73 motor (in the sling) and the older generation M70. For anyone transplanting these motors into another car, and/or building something custom, where you need more ground clearance, you need the M70 pan.

The older M70 motor has a shallow (only about 2 3/16") cast aluminum upper pan, and a fairly deep (4" or so)sheet metal sump.

The newer M73 motor has a deeper cast pan (around 4"), and a shallower sheet metal sump.

For the dry sump system, we'll use the older shallow cast pan, trim off the side extensions, weld it up, resurface it and put in the fittings for the scavenge pump. We should be able to gain about 4" by doing this, and of course that will also benefit the CG of the car. Not that a 40" high car has many problems with its CG anyway........:boggled:
very interested to know if there will be any problems with running the g50 in an inverted setup.... have considered a g50 for my next tube frame project after my v12 supra is done.
It's a very popular box for the GT40 replicas and is frequently done like this. My friend has a 347 SBF race motor in his GT40, and he estimates he's putting around 500 lb-ft into his G50. Apparently the trick is to overfill them a bit to make sure the R&P are well oiled. Some even put external pumps and coolers on them, but that seems OTT to me for street applications. Lots of good info about the G50's on

If you can find a G50/50 for less than $5000 US, buy it now even if you don't need it. The supply is dwindling fast and you can always sell it for what you paid for it, or more later. My box is a G50/03 which isn't as strong as the G50/50, so I'll probably have to put another $1.5 to $2.0K into it for strengthening.
Not too fancy - there are several outfits that make shifters and linkages for the GT40's. Most for the G50 box are cable actuated, and they work well. I drove my friend's GT40 replica with the 347 motor and G50/50, and cable actuated shifter, and it felt very positive and responsive. When you're ready, I'll put you in touch with the people that make the shifters - one of the best is there in Australia (little wonder, eh?).
the GTR may not be the prettiest car on the road, but its alot lighter than a GT40 replica and it has a great history. they used those damn things to test the McLaren F1 drivetrain. which is also a V12 and a transaxle. as a matter of fact, the V12 used in the F1 is the same base block as the engine your using.