Let's talk bottom end rebuilding.

[lolcantturn]

I'm picking up an M50 Vanos long block from a good member here (gp.plus) which will be the candidate of a long term "whatever money I have left from my paycheck" turbo build. It has 180k, which I'm sure is not good preferred since I plan on getting the block O-ringed and making >400whp.

Now I'm curious, is it better to rebuild this 2.5L M50 bottom end with new piston rings, bearings, and main bolts, or rather find a lower mileage 2.8 M52 block?

As far as bottom end rebuilding goes, to what extent will machining play a role? I assume that I simply cannot buy piston rings, but find out the exact measurements of the cylinder and custom buy the rings?

[VinniE30]

What's wrong with the NV M50 you already have?
I would go with the 2.8 M52 anyway, you won't have to run as high pressure as with the m50 to make the equivalent power because of the larger displacement.

[lolcantturn]

What's wrong with the NV M50 you already have?
I would go with the 2.8 M52 anyway, you won't have to run as high pressure as with the m50 to make the equivalent power because of the larger displacement.

I would be building the motor turbo outside of the car, this means I can still drive it ;)

And that's exactly what I was going for.

[328ijunkie]

M52. /thread

[NbAmTwE]

isn't it aluminum though? M52 I mean.

[328ijunkie]

all except the 97-98 Z3s had cast iron bottom ends. M52TU's were all alum.

[Beej '86 325es]

Just be careful which M52 you buy. Years back I bought a Z3 aluminum block bottom end that turned out to be an M52TU from a '99, which has different oil/coolant passages. '97-'98 should be ok though, as 328ijunkie said.

[Adrian_Visser]

^^^Not for boost. The alloy blocks have a habit of pulling head bolt threads under boost, besides good luck finding one if that was what you wanted. They are pretty damn rare.

BTW I choose option C) use 2.5L block and 84.5mm bore and s52/m54 crank. This gives you a 3.0L Franken stroker with lots of meat between the cylinders for HG sealing.

[NbAmTwE]

^^^Not for boost. The alloy blocks have a habit of pulling head bolt threads under boost, besides good luck finding one if that was what you wanted. They are pretty damn rare.

BTW I choose option C) use 2.5L block and 84.5mm bore and s52/m54 crank. This gives you a 3.0L Franken stroker with lots of meat between the cylinders for HG sealing.

This is a good idea, I've always wanted to do a Frankenstein motor.