VW W12 to Porsche G86.20 transaxle

Hi there,

I am looking for the flange and bolt pattern of the W12 engine:


Does anyone have that?

I am mating this to a Porsche G86.20 gearbox:


Can anybody help?

This engine/transaxle combination is ultra compact. I measure less than 80cm between the output shaft and the most forward point of the engine.



KEP can probably furnish an adapter but I doubt if they will give you their drawings.
I made a bellhousing to couple a diesel generator head to a Nissan MR18 1.8L engine. Believe it or not, it was easy.

I took a good pic, straight on of the nissan engine, and imported it into CAD. I traced it with a PLin, and circles for the bolt and dowel holes. I then scaled it to the exact measures dimension from dowel to dowel and cut it on my CNC plasma table.

The genorator head was easy as it was a circular SAE standard flange.

So I then bolted a template of the SAE flange to the flywheel and welded segments to mate the 2. I then did the standard bellhousing alignment procedures, welding the bushings at the dowels after the runout was zeroed and tadah!!!

I say all of this to say, with cad and a CNC mill you can easily do this.

Otherwise, KEP can make it for you.

Looks like a tasty powertrain. Hope to see you take it to completion.


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Thank you for the replies! I contacted a few folks - seems that I am on my own with this. Few learnings over the last days:

The G86.20 gearbox can fit a flywheel with a diameter of about 280mm. Question: is this the same for other Porsche gearboxes or do some allow for a larger diameter flywheel?

The flywheel of the W12 engine measures 310mm.

Since the starter motor of the W12 engine engages in the 310mm flywheel, I cannot get the G86.20 "over" the W12 flywheel/tooth gear for the starter motor.

There are complete clutch packages for the G86.20 gearbox that can hold enormous torque:

671 lb-ft

480 lb-ft

At this point, I will have to measure up the flange of the G86, the flange of the W12 and then I need the distance between the boxter engine flange and the crankshaft flange as shown in the images.

With these info, I can design it all up in CAD and get it machined.

Any input here would be greatly appreciated!

Could have done this easier but the sound of a 12-piston engine is just something I dont want to miss in my Countach (re-)build.


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KEP adapters usually include a spacer of about 1", enough for them to make you a stepped flywheel that can use the W12's gear ring, and a smaller clutch assembly. They advertise that if they don't have it, they'll make it. Some instances, the starter will bolt to their adapter plate if there's a void in either the engine or transaxle that will fit a starter.
Thanks for that Information, really appreciated!

It is interesting to see that VW has chosen an external crank trigger wheel, mounted on the flexplate. You can see that the crank bolts have asymmetric spacing, just like the flexplate rivets and the crank trigger wheel itself. The crank trigger wheel has nominally 60 teeth, and 2 teeth are missing, so it is a "60-2" crank trigger wheel.


The Holley EFI system that I am planning to use has that option, although I do not think it supports sequential injection and ignition on V12 engines. That means I have to spoof the EFI controller that the engine is a 6x cylinder engine and run wasted spark ignition (spark plug always fires on TDC no matter if it is in the power stroke or the scavenging stroke). The nice thing about running it in 6-cylinder wasted spark mode is that I can place the cam trigger also on the crank. Typically, this is not possible as the cam gives 1x pulse for 2x crankshaft rotations. But if you run the engine in 6-cylinder wasted spark mode, the crank trigger wheel has double the teeth - so if I chose to run the EFI with a 24-2 crank trigger wheel, I need to make a crank trigger wheel with 48x teeth, and I need to cut out two times 2x teeth opposite from each other (4x in total). Then there is a "second row/second sensor" right next to the crank sensor that only gets one signal (1x tooth) for the full duration.


Done that before on a different V12 but that was a long time ago...
I know it works but cannot remember the exact details!
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Could have done this easier but the sound of a 12-piston engine is just something I dont want to miss in my Countach (re-)build.

Just curious, is the W12 an even firing engine like 60 degree V12s? If not, will it sound like a traditional V12 or more like a V8? If doesn't sound like V12, is it worth the hassle of mating it to a transaxle that it looks like you'll need to go to? Again, question is more curiosity than anything. I had people suggest using a W12 for my Miura project. I didn't go that way just because W12 isn't a common engine in my part of the world so I didn't investigate piston firing dynamics or exhaust sounds for it.
Hi Joel,

The W12 is an even-fire V12, and it has exactly 60 degrees of rotation in between the firing events. The associated mechanical assembly is super complex - The centerlines of the bores do not pass through the crankshaft axis, in an attempt to "make the two cylinder banks that are merged into one cylinder bank more parallel". The engine still uses two conrods on each crank pin, but that means now that the pin cannot be in the same location for both conrods. You need a "split conrod" design to get the even 60 degrees firing order.

I have re-built too many engines now (BBC, SBC, BBF, LS2/3/7) that are "simple". This all gets boring to me. The W12 is a miracle of engineering in all its aspects. Ultra complex - both intake and exhaust cams are variable and they purposely run both cams in "high overlap" such that the fresh charge purposely has some exhaust gases left which helps emissions.



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The big down-side is that you cannot freely program the ECU and all the associated sensors on the engine. I do not plan to use any of the VW electronics as I want to be in charge of all parameters myself - using a Holley EFI system...

Last but not least, driving other modern V12s - I really do not enjoy all the power they make. If you drive an old V12 from the 80s with only 300-400hp you can enjoy all that sound at 6000 rpm while still going forward safely. None of these modern V12s can do that anymore - by the time they make awesome sound, they go so hard that you are about to kill yourself. If anything, I want to throttle power down with this project so I can drive at high rpm and enjoy that V12 sound while still being safe. I do not need/want more than 300hp but I do need that V12 sound at 6krpm.
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This crankshaft is making my brain hurt.

So, they have to split the throws to make up for the out of line pistons in the bank. And the crank still has 7 mains, and 6 pairs of rods.

Are the banks symmetric with the first cylinder on each side both being in inside or outside? Not sure how to ask the question and I have no nomenclature for how the cylinders are numbered.

I've seen cutaways of this engine and knew about the lopsided piston heads, but the crank spacing never occurred to me. wondered if the piston bores intersected, but by the timing there was never 2 pistons there to crash.
Everything on this engine is a work of art. You need to check out the crank in life - its forged, super light-weight, superbly finished - just the exact opposite of an LS crank in every view you look at it. An order of magnitude more complex. It amazes me that they could mass produce these engines. These W12s (and of course also the W16 for the Bugatti Veyron) are the most amazing engines there are in my view. How it god's name can you pick them up for a few grant from a junkyard? This is heaven on earth. I would buy more of these engines if I had more space!

Here a view of the firing order:

Its amazing how short this thing is - 6L of displacement and the engine block is just a bit over 500mm long.
Interesting. If they made the centerlines of the banks 60 degrees apart they could have adjusted every other throw the 12 or 15 degrees the other cylinders were off and not messed with the split rods. Instead just have one bank follow the other by 300 degrees and have 2 I6 fireing orders.

She is a beauty, and compact enough it could even me mounted transverse, but that transaxle would be hard to find.
Interesting. If they made the centerlines of the banks 60 degrees apart they could have adjusted every other throw the 12 or 15 degrees the other cylinders were off and not messed with the split rods. Instead just have one bank follow the other by 300 degrees and have 2 I6 fireing orders.

She is a beauty, and compact enough it could even me mounted transverse, but that transaxle would be hard to find.

Okay! Now I understand your point! The crankshaft was the most difficult thing to get right - due to its length and probably also the slightly reduced strength through the split pins? The early development engines had crank failures (fatigue failures). It shows you however, how thin and mass-efficient crank webs can be - if you come from the crude V8 world, you might think that these monster webs are "required" - but that is not the case. The crankshaft of a V8 is so "fat" and "overweight" that you can easily get away with cheap, cast material. I first noticed how beautiful cranks can be when looking at the Porsche Boxter engines, which also have really narrow web thicknesses. I investigated more and realized that the webs can indeed easily be half the thickness of the journal bearings... then came the W8/12/16 engines.

On the transaxle: there are a few kit-cars over here that put 1000hp through the W12/W8 Audi A8 transaxle. The Audi A8 came with the W12 engine and all-wheel drive - they made a transaxle for the W12 that resulted in the shortest engine/transaxle combo ever. You can see it below - its a fast-shifting automatic, electronically controlled (can use tip-tronik to manually advance gears on the steering wheel):






You can see that the differential is mounted basically "in the bellhousing" of the transaxle.

It is the shortest transaxle that exists. There was a guy here in Germany who used the W12 and the Auti A8 transaxle for Lambo Murci replicas and he pushed them close to 1000hp. He claimed "faster, significantly cheaper and way more reliable than anything Lambo" but he only made 8x cars or so of them before VW shut him down with law suits on copyright (VW bought Lamborghini and they employ lots of totally useless lawyers to prevent awesome things from happening - sort of my primary reason not to purchase anything VW/Lambo new anymore). The chassis was more spaceous as he modified the rear firewall and the trans tunnel was munch smaller thanks to this engine/transaxle combo.

You can pick up a W12/transaxle combo for just a few grand...
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Ok, contacted a few machine shops and clutch specialists

"We cannot make you a custom engine adapter kit for this engine to a Porsche Boxster transaxle, there is no placement for a starter and there is not placement on the custom flywheel that we would make for the Porsche Boxster use to put a trigger wheel that you are showing that engine requires."

I am on my own!
What a bunch of pansies. Use the VW starter on the block, and if you have to, ditch the 60-2 pickup on the flywheel and mount a 36-1 on the front pulley somehow. There's 10 ways you could do it, I'm sure.

You may have to scavenge the ring off of that flex wheel and mount it on your flywheel, but this really isn't that difficult. I think you could do it with a wood router, a couple of jigs and carbide router bits. They cut 6061 like butter if you don't try to go full depth in one pass. The only thing that is a critical is keeping the 2 shafts aligned within .003" or so.
If you have access and know how to use that thing, the CNC mill should be in your reach as well.

One point to bring up, if there is play in the input shaft, make sure you're measuring it centered in it's range or average with it at it's extremes.

You can do this.