m20b30?

Tue Nov 22, 2011 7:15 pm

Hey guys, just woundering if its possible to fit the 3.0l crank from the m54 into the m20?? Im curious as i know the internals from the m54 can be fitted into the m50-52 engine and that the crank from these engines goes straight in the m20.

The only thing i would think that might stop it working would be the rods catching the side walls of the bores on the stroke. Anyone tryed it out?

Wed Nov 23, 2011 1:31 pm

yes, has been done with mixed success.

Wed Nov 23, 2011 2:09 pm

http://www.iemotorsport.com/bmw/E30-engine.html

Fri Nov 25, 2011 9:32 pm

Who has done this then with mixed success. I think if you are going to all that trouble you might as well bore out to 85mm and get some proper pistons made.

Sun Nov 27, 2011 5:17 am

This info is all on the web for those who look, but if you're lazy here it is:

You can have a selection of crankshafts for your m20:

Stroke: Engine:
75mm M20b25
76.5mm M20b23
81mm M20B27
84mm M52B28
86mm S50B30 (US spec)
89.6mm M54B30

Correct me if I am wrong this is just off the top of my head.

Max capacity is 3.1 litres, however; you could do an offset big end regrind with smaller rod bearing diameter to gain an extra 1mm stroke, I know some Datsun guys doing this.

So, take the M54B30 crank at 89.6mm, carry out the regrind, and achieve 90.6mm stroke. So with 86mm pistons, someone do the maths for me, that must be 3.2litres.

Poor little M20 is now machined to an inch of its life, but what a motor!

Sun Nov 27, 2011 5:28 pm

Cheers for the info, ive just been looking into this a lil more.

Mmm... A 3.2 m20 sounds fun. Not sure if i would go that far though tbh, ill have to do abit more reading i think.

Isn't the US m3 engine an s52b30 or s52b32??

Sun Nov 27, 2011 10:11 pm

eta wrote:Who has done this then with mixed success. I think if you are going to all that trouble you might as well bore out to 85mm and get some proper pistons made.

http://bit.ly/uSgiaV

my personal opinion is that you are best sticking with sub 3l displacements on the m20, if you feel you really need that much more power then the only way to go is 24v.

the 3l motors are fine, just massively under valved (in terms of area available for induction) which results in a sub optimal motor when the m50 requires less work to get to these capacities with greater performance from the end result.

as far as going for 85mm pistons, thats all well and good provided you can get pistons of agreeable quality, with the correct chamber profiles for and agreeable price.
most people dont have £700 to spunk on pistons.