e30 2.5 and 2.7 stroker build help

[travis_e30]

I love my e30 but the stock eta motor isn’t cutting it, what all is needed from a 2.5 for a stroker build and can I use 1991 pistons from a 325is?

[digger]

eta 81mm stroke crank
eta 130mm rods
m20b25 pistons (may need to trim the bottom of skirt depending which exact brand (KS or Mahle) they are as there is like 4 or 5 skirt lengths/types.
deck block approx ~2mm
adjustable cam gear (optional)
m20b25 885 head
272 cam (optional)
M30 injectors or similar
nice set of headers and exhaust (optional)
chip or PNP ecu
the rest from a m20b25

[travis_e30]

Can you use 1991 325i lightweight pistons?

[ADEN]

Can you use 1991 325i lightweight pistons?

M20b25 =Domed M50b25= Dished

M50 pistons might work better with your stock head 773 but with 885 head your compression ratio will get down badly by almost 2.

Digger gave you the perfect combination possible from 2.7 eta+2.5 i.

[ForcedFirebird]

M20b25 =Domed M50b25= Dished

M50 pistons might work better with your stock head 773 but with 885 head your compression ratio will get down badly by almost 2.

Digger gave you the perfect combination possible from 2.7 eta+2.5 i.

1991 pistons from an m20 would work.

[ADEN]

1991 pistons from an m20 would work.

MY bad i tought 91 was already e36.

[ForcedFirebird]

MY bad i tought 91 was already e36.

The last e30's rolled off the line in Jan 1993. The e36 was built as early as Nov 1990. In the late years you would get an e30 if you ordered a vert, and an e36 otherwise since the verts had to go to Baur for the conversion. This is why the verts have diving boards longer than the others.

[digger]

Can you use 1991 325i lightweight pistons?

All m20b25 pistons can be made to work essentially. If they are the lightweight they probably have the streamlined skirts. Here are some skirt types but there are others. The one on the right i think offers most clearance and is probably what you have.

its easy to trim the bottom if you happen to have a longer skirt variant, just weight match them afterwards and removed burrs etc

[E30Eric]

My setup from a little while ago. It's pretty solid. 288 cam though. I've pulled it and am going LS6TT, Tremec 6spd, why not. Thinking of putting the 2.7 in my Nissan D21 4x4. I love the sounds it makes with the Ansa and Schrick 288 on MS with the wasted spark setup/removed MAF.. Good luck on your build! 3.73 LSD is a game changer with the combo also IMO. I've saved the 2.93 gears for the upcoming build though.

[ForcedFirebird]

Late model pistons will be the center in pic above. Mahle still look like that today. Last pistons I installed were made in late 2020. There actually was s shortage of +.5mm world wide in late 2018, ended up getting old stock from various suppliers that were made in 2010-12-ish at the time.

EDIT: travis_e30, you have the same pistons as they are produced today. They actually clear the 81mm pretty easily, the b28 84mm, not so much. Either way, I have shaved stock pistons to clear bob weights, never had an issue. Chuck them in a lathe, turn the skirts, re-balance.