m90 stroker

[navytapaul]

I found that out too, they're all pretty much the same with the exception of bore and stroke for the m90.

[slammin.e28]

I found that out too, they're all pretty much the same with the exception of bore and stroke for the m90.

Yup.

My issue, M90s put out close to B35 #s. So why not B35?

But they are so cool, and from what I hear, more fun to drive. Short stroke, rev happy, bigger bore. Totally different experience from a B35.

I ran my M90 head on a B34 for a bit, it wasn't half bad, then again, the only real difference is the cam, IIRC. Valve specs are the same as a B34....but hopefully I'm wrong. I should take it back apart and mic them out.....

[navytapaul]

I was on the same thought path too, after stroking an m90, why not just punch out a b35 since it will be the same engine?

[LJ851]

I was on the same thought path too, after stroking an m90, why not just punch out a b35 since it will be the same engine?

M90 block has thicker cylinder walls. Other than that, no reason.

[slammin.e28]

M90 block has thicker cylinder walls. Other than that, no reason.

Back when BMW was doing M30B28, B30, and B32, the M90 was a big deal. Not to mention it was Euro only.

Now, since they peaked out the M30B35, which looks like the culmination of the best parts of all of the M30 engines, really not point to M90 other than a coolness factor....and that's enough for me.

[kronus]

Why not keep the m90 geometry? Its powerband is higher up than a B35 because it's short-stroke...

[Jb325is]

Why not keep the m90 geometry? Its powerband is higher up than a B35 because it's short-stroke...

Dat compression bump. But yeah, I agree kinda

[navytapaul]

I was thinking that as well, I know some race engines are short stroked for that reason.

[LJ851]

I was thinking that as well, I know some race engines are short stroked for that reason.

The M30's strong point is torque. Capitalize on this with more capacity. Gaining another 1000 - 1500 useable rpm is expensive and hard work. I had a 3.7 liter that was a torque monster and pulled hard right up to 6300 redline.

[navytapaul]

so is the m90's and it doesn't run out of breath as early as a b35 does. Does the short stroke of the m90 cause this since the heads are identical except for the bigger valves in the b35 head? Almost seems like since the m90 and b34 heads are the same and the m90 and b35 cams are the same, why not put a b35 cam in a b34 head and drop in some piano tops for a nice high comp motor?

[kronus]

B35 head flows better than B34 due to bigger ports, not just bigger valves. The whole B35 intake-exhaust channel is a lot less restrictive than B34.

Really, the optimal thing is going to be an M90 block and rotating assembly, B35 head and custom (forged, piano-top, jizzed-on-by-underage-unicorns, etc) pistons to hit whatever CR you're aiming for.

And yes, the M90 powerband is up higher due to the shorter stroke. I'm not really sure if it's sensible to modify a motor to have longer stroke and then complain that the powerband moved down in the RPM range.

[navytapaul]

I forgot about the ports being bigger as well. Did BMW ever make a dirty m90 like they did of the b34?

[kronus]

nope, the m90 didn't have a dirty version. There was an L-Jet and a Motronic version, and according to some legends the L-Jet one revs faster, but I have not verified this.

[navytapaul]

I heard that too, as well as a small and large m90 head. L-jet got the small head and motronic got the large one. Looks like I'm going to find an m90 short block and some b34 mounts.

[LJ851]

I forgot about the ports being bigger as well. Did BMW ever make a dirty m90 like they did of the b34?

The M90 is the "dirty" B34.

BTW, there are two M90 heads, one has B34 shaped ports and the other has almost B35 shaped ports.

remember, the M90 and B35 have similar peak HP numbers, the B35 just has a fuller bottom end.

For a mild build like you are talking about, the B35 IMO is the best choice. Best breathing, most torque, best ignition and fueling, lightest block,most readily available.


Are looking for 220 at the wheels or engine?