building stroker need help!

[blink977]

I'm starting this thread cause I'm fully messed today with a lot of combinations of rods and piston.
the case is i'm building m50b20 stroker for my e30, i matted a 2.5 liter 75mm crank into b20 block and now looking for optimal compression ratio. i've tested everything:
m50b20 vanos pistons with non vanos 135mm rods, m43 1.8 liter engine 140mm rods with vanos pistons, m20 pistons with m20b20 130mm rods, all combinations was shitty, last m20 pistons with rods made a 12.9:1 compression ratio, and i guess it is quite bad for a daily driven engine without knock sensors.
I even dont know what to do now, shave piston dome, or what? anybody can correctly calculate a 75mm crank into a b20 block, 130mm rods and m20b20 piston with dome? i'm getting somwhere 12.95:1 compression ratio and 2.26 liter with my calculations.
second problem is i can't find spec for the m50b20 non vanos cylinder head volume, some guys says its 29, someone - 32, just like a m50b25 head volume, but it gives me a huge difference in calculated compression ratio, someone can tell how much it is?
my goal is somewhere around 11.5:compression ratio
someone heard about m50b20 non-vanos siemens engine managment, without vanos but with knock sensors?

[SpecM]

don't use m20 pistons in an m50. The valve releifs will be all wrong for a 4-valve motor

[blink977]

don't use m20 pistons in an m50. The valve releifs will be all wrong for a 4-valve motor

i know that, but maybe valves even won't touch the piston.

[nando]

the entire combustion chamber shape is wrong. the M20 uses a hemi combustion chamber, the M50 is pentroof.

surely M50B25 pistons aren't impossible to find?

[lennon]

i have some m50b25 pistons you can have for 75$

[blink977]

what are you talking about? I do have m50b25 pistons but don't need them cause they are 84mm diameter vs b20 80mm. i'm not going to bore the block

[lennon]

well i have no clue what you're trying to do, because its impossible to read that first post.

[blink977]

ok, promblem solved. m50b25 vanos pistons, m43b18 140mm rods, block shaving 0.3mm and i'm getting 11.3:1 ratio.

[sharkfour6]

ok, promblem solved. m50b25 vanos pistons, m43b18 140mm rods, block shaving 0.3mm and i'm getting 11.3:1 ratio.

I know this is an old post by why didnt you just do the S50 clone and use M54B30 crank, rods, and pistons if you were going to bore out the block to 84mm. I have read that this setup makes well more than the US spec M3. Plus you can use normal petrol too.