Ill just copy bits from some of my posts on dtm
ouch, the secret is out about US cranks now, ive spoken to a couple of suppliers in the US this afternoon who had cranks 6 month's ago to find they dont have any at all, now they are selling like hot cakes
Damn E30 owners :p
The wildly expensive IE kit is actually looking like a good price considering the $2300 US cost to replace a 3L US crankshaft
86mm is about the largest (80 thou) rebore i would go on an M20 block without sonic testing to find out just how much metal actually exists. With the crank that will give you 3L. Im kinda leaning towards the 2.8L crank and a piston / rod combination from other engines at the moment, a change of pistons changes deck heights really easy, with one piston you can drop 1mm+ below giving you a good compression ratio for a turbo, then with another change you can be 1mm over with a raised crown and bumping the compression ratio up for a good NA engine. You would be surprised the number of components that will actually fit inside an M20 block, its because the M50, M52 and M54 engines are all derived from the same design, that being the good ol M20
Edit: You will probably find the bmwworld weights might be for a complete engine. The bmw weight list is for an engine minus fluids, manifolds and accessories. So basically it's just a long motor. Dont forget that some of the US engines had iron blocks too, so there is a bit of a difference between some US and euro spec motors.
M20 crank left, M50 crank right.
Same again, can see the difference on the nose, M20 has a section for the seal, M50 one doesnt.
M50 crank sitting there, bearing cap installed. Can see the first bearing lines up fine with the standard M20 block.
Pretty average pic, but you can see the M50 crank sitting in there with no problems. Again, its because the main bearings are the same size.
Can see the sleeve installed, plus the reason why you need it (the seal).
Crank + pistons installed, bolted down.
Its only the 3L cranks from the US spec cars that work, we didnt get a 3L M50 or M52 here, so you are pretty much limited to an M54 motor which isnt going to be too common over here (not in parts anyway). Our M3 motors arent any good for this, they are euro spec motors which have a totally redeveloped bottom end, bearing sizes are larger so it wont fit.
So, no, S50 crank wont be any good, you need the S50US item, or a 3L crank from an M54.
There are no pistons and rods you can use that will fit. You can use the standard 130mm (320i/323i/325e) forged rods or use the 135mm 325i rods (or similar M52 length items) but you need a custom piston to fit.
When using the 135mm rods you need a piston with a compression height of around 28.8mm (i can give you the exact figures, i just need to look them up in my book), with the shorter 130mm rods its obviously going to be 5mm more (33.8mm).
Pros are increased torque and horsepower that is going to go with it. Going to make for an M20 torque monster.
Cons, cost, machining, need to do your research with head porting/polishing and need to match cams to suit. Increased piston speed so you should plan for the engine to reach high revs.
Edit: forgot to say im building a 3L one now (just waiting for the crank to arrive from the US, should be here in 3-4 weeks), with 45mm ITB setup, plus a nice large holset turbo to bolt on to it once its built
Ive got the throttles already, they arrived last week
should be interesting
S50 crank which I think I'd be stupid to turn down and I'm just wondering what else I'll need, I've done a load of research and think I know but just want to hear what you guys have to say.
Which I would be happy to do but it will just mean it will take a lot longert to do as I will only be buying stuff as and when I can afford it.If I do buy it I envisage just building up the engine will take 12 months, unless I make loads of money!
