different compresion ratios?

[T Verdier]

I read in my performance bmw mag today that my 87 m20b25 has a higher compresion ratio than a post 88 m20b25 is that just in a euro car or what?

[nando]

yes, they had the option of cars with no catalytic convertors - those cars got higher compression ratios. all the catalytic convertor cars are 8.8:1, including our '88s.

[akorcovelos]

what was the higher CR on the euro cars? Was this achieved with different pistons using the same 135mm rod?

[nando]

9.7:1 I think. and yes.

before you go on a wild goose chase though - the bump in compression only made a 2-3hp difference in peak output. I've never seen a dyno comparison between the two engines directly to know if the total area under the curve for the high-comp B25 is significantly larger. My guess is no, because eventually they built all M20s with 8.8:1. the stock cam profile isn't agressive enough to take advantage of high compression.

[akorcovelos]

yeah, I'm way past sourcing pistons, just curious. I wonder what the motivation was behind going that route?

[T Verdier]

yes, they had the option of cars with no catalytic convertors - those cars got higher compression ratios. all the catalytic convertor cars are 8.8:1, including our '88s.

not in the U.S. right? because i dont think they would pass emissions without it

[SpecM]

not in the U.S. right? because i dont think they would pass emissions without it

nope, just in europe

[T Verdier]

the early engines are marked 84 6e and use a higher compression ratio of 9.75:1 the later engines (post 88 ) are marked 84 6k (the K stands for katalyser) and have a lower compression of 8.8:1. now this is European so witch do i have with U.S. spec 87 325is?