head for my m90

[hikjer1]

im currently rebuilding an m90 and i was thinking about heads for it. I know that the reason why the engine is so great is because the compression is so high. Does anyone here know how using a b35 head (for instance) would change the compression? The b35 head flows a lot better so i figured if the compression wasn't changed much then maybe this would be a good option. Any opinions would be great...thank you!

[Mike W.]

The B35 head lowers the compression significantly. I forget exactly, but IIRC into the 9.3:1 range. You know the matra, search... it's been discussed before a few times.

[hikjer1]

sorry, i should have looked...but thank you for the info

[wkohler]

According to a post by Big Bronze Rim, he said that the B35 head on a Green B34 will lower the compression from 8:1 to 7.45:1. I can't think clearly enough right now to extrapolate that to the Dirty motor.

My guess is:

solve .55 (the difference between 7.45 and 8)/8=x/10 for x and you get .69, which would mean you'd be in the 9.3:1 range as Mike suggested. Still nothing to sneeze at, but it kinda undoes a lot of the work to get to 10:1

[Brad D.]

You're damn close Chris. My M30 CR calculator I made says 9.11:1 and yes, a green b34 with a b35 head is right at 7.45:1. FWIW, the b35 head has 65cc combustion chambers and the b34 head has 58cc combustion chambers. I don't know for sure, but would bet the m90 is close to the b34.