Euro m20b25

[Jargo]

So I have a 86 325i Euro Convertible that I'm parting...and I can't decide to keep the euro motor to swap in my 86 325es, or try to sell it. This thing runs strong! I'm really impressed at the power it has over every other US 325i I've ever owned or driven. I've done a bunch of searches and don't see many people running these euro motors so I was just hoping for some opinions on it.

[323iNathan]

the early euro b25 has higher CR pistons and has about 1hp extra than a later low CR b25 (listed, no idea how much the difference really is)

We didn't get early 325's down under, just 323's so I've never driven one...

[Sirotto]

So I have a 86 325i Euro Convertible that I'm parting...and I can't decide to keep the euro motor to swap in my 86 325es, or try to sell it. This thing runs strong! I'm really impressed at the power it has over every other US 325i I've ever owned or driven. I've done a bunch of searches and don't see many people running these euro motors so I was just hoping for some opinions on it.

The pistons are the only thing worth much. I would keep it and replace any eta in any car I had.

[Jargo]

How much do you think the pistons are worth?

I'm surprised its only rated at 1hp more than the US b25, it really feels quite a bit quicker even in the heavier vert. The throttle also seems very responsive, maybe just the result of higher compression and lack of old (clogged?) cats on every other 325i I've ever driven?

I'm thinking with a few mods this might be quite a powerful motor. Either that or use the pistons and m52 crank to build a high compression 2.8L...hmm

[riceh8r]

I'm thinking...use the pistons and m52 crank to build a high compression 2.8L...hmm

yeah...^^^this FTW !!!

[nando]

you need later short skirt pistons for the 84mm crank, so they won't be any good to you there.

[Jargo]

you need later short skirt pistons for the 84mm crank, so they won't be any good to you there.

Hm, been doing a lot of research on this setup and haven't heard that before. Do you have any links or other data on this? I could probably always cut them down and balance them if this is the case, but interested in finding out more.

[nando]

you'll have to cut quite a bit down - even the short skirts are close.

I'd ask "winfred" about it, he's done it most recently that I remember.

I just don't see the miniscule change in CR being worth it. you still end up with ~9.5:1 with the later short skirt pistons and they don't require nearly as much work. if an 84mm crank is truely in your future, I'd sell the euro pistons to somebody who thinks that half a point CR increase is a big deal.

[Jargo]

I understand what you're saying. From what I've read the CR with the Euro pistons would be around 10:3-10:5:1. Is this not a significant enough increase to make the extra cutting worth the effort?

I will try to contact winfred, thank you.

[nando]

if you're going to use a stock or mild cam, it's likely too high. over 10:1 is 280+ degree cam territory.

[Jargo]

I was thinking a 288 would be in order, yes. A stock cam would probably work but would not make much top-end power and timing would have to be adjusted way off, correct? (megasquirt)

[nando]

yeah, 10:1 is too high for a stock cam. a 288 would work well.

you can also cut down the crank counterweights. as it turns out, the 84mm crank has the largest diameter out of the cranks that fit in an M20. Some guys have to clearance the block for it to fit, but not the 89.6mm S52 crank.