Iso/looking for m20 stroker

[Lars30]

Anyone have a built stroker motor that I could put in my 1988 325iS. Not looking to spend the $/time sourcing all the parts. Saw a 3.1 Stroker built ready to go on the FB forums in the summer for a very good price, sold immediately and still kicking myself. Just wanted to see what's out there

[zaq123]

Anyone have a built stroker motor that I could put in my 1988 325iS. Not looking to spend the $/time sourcing all the parts. Saw a 3.1 Stroker built ready to go on the FB forums in the summer for a very good price, sold immediately and still kicking myself. Just wanted to see what's out there

Unless reputable builder, Id be concerned how it was built. I'm sure you won't get any warranty or a warranty that actually will be honoured. My recommendation is to DIY if you have the ability. It's not that complicated actually and plenty of info on the forum. 3.1 is what you want? I'd go for 2.9 with 10:1 Mahle pistons. If your head/block is ok, you will save a lot just reusing those as well. Source parts, find a machine shop and once parts are ready, it's pretty straight forward process. You can build one at around $4k+ budget using quality parts and your existing engine. Pistons, cam, rockers and the actual machine shop work being the largest part of the budget. To buy good quality built stroker, I'd expect to see double that if not more.

[AWDBOB]

Unless reputable builder, Id be concerned how it was built. I'm sure you won't get any warranty or a warranty that actually will be honoured. My recommendation is to DIY if you have the ability. It's not that complicated actually and plenty of info on the forum. 3.1 is what you want? I'd go for 2.9 with 10:1 Mahle pistons. If your head/block is ok, you will save a lot just reusing those as well. Source parts, find a machine shop and once parts are ready, it's pretty straight forward process. You can build one at around $4k+ budget using quality parts and your existing engine. Pistons, cam, rockers and the actual machine shop work being the largest part of the budget. To buy good quality built stroker, I'd expect to see double that if not more.

I'll x2 this

I've done several 9.4:1 2.7s with mild cam, and one 10.5:1 3.1 with head work. The 3.1 was very expensive to build, and anything similar you'd actually want to put in your car isn't going to be cheap, even if its secondhand. For example, the one "cheap" 3.1L m20 that sold a few years ago ended up being a paperweight and had to be reworked from top to bottom due to several aspects of the initial build being done incorrectly, parts chosen poorly, etc etc. Most of the 3+L M20s built in the past 10+yrs didn't use pistons with the correct dome shape so they detonated to the high heavens and didn't make any substantial power once in the car.

You have the 4-6K ~175whp M20 club which is typically a 2.7-2.8 with a mild cam and no head work. To do a nice 2.7 or 2.8 is relatively simple for most machine shops minus the required deck cutting, and you can use your existing pistons, although it's definitely worth going 84.5mm while the pistons are available, which they are (11251714810).

As soon as you want to shoot for 200whp+ things get very expensive, as you're now considering head work, custom pistons, pricier valvetrain, ITBs, headers, etc etc. It's a huge cost that requires additional $$ put into most other ancillary systems to support it, in addition to time. You can count the guys who know what they're doing with M20 headwork on one hand so they're booked far out. If you're loaded with time and $$, it can make for a great experience. If you're not, I wouldn't go this route.

Be very cautious buying a cheap used stroker M20, should you find one.

[MR 325]

There's these guys called BimmerHeads, they build stroker M20 engines and sell the parts to build them too! ;)

[McGyver]

There's these guys called BimmerHeads, they build stroker M20 engines and sell the parts to build them too! ;)

Someone needs to open a shop called BimmerBlocks so we can get the bottom end too Side note, thanks for the quick shipping on the package to Philly. After several years and a cross-country move, I'm just about ready to start assembling my engine!

OP: When I was getting ready to pull the trigger on some stock 84.5mm pistons, I was cautioned about going for a 3.xL m20. I already had most of the parts to make a 2.7i and I was wondering if it made sense to spend the money to go bigger. As others have stated, the stock head and intake are a major restriction for a large displacement m20. So you either need significant work so that it'll flow well, or you end up spending significantly more money with marginally more power than you'd get from a 2.7/2.8/2.9. I plan to turbo my 2.7i and then build an NA 10:1 2.9L with the engine that's in the car so I have a replacement if/when I need it. (or for the next e30)

[strickland]

I have wondered about upgrading air flow on the M20. Many have said that the stock airbox performance cannot be improved with a cone air filter.

for a total n00b (me) — what does it take to increase the intake & exhaust manifolds? Just curious.

[82eye]

I have wondered about upgrading air flow on the M20. Many have said that the stock airbox performance cannot be improved with a cone air filter.

for a total n00b (me) — what does it take to increase the intake & exhaust manifolds? Just curious.

you can probably gasket match them. on my car we did a street port which really only involves cleaning up any rough parts and a gasket match. it's not a mirror polish or anything. there are guys on the board who have done much more head work and have done it more professionally. we didn't go that deep as no one here has any experience with the m20 or even bmw at all.

[digger]

I have wondered about upgrading air flow on the M20. Many have said that the stock airbox performance cannot be improved with a cone air filter.

for a total n00b (me) — what does it take to increase the intake & exhaust manifolds? Just curious.

throw them in the bin

[lambo]

There's these guys called BimmerHeads, they build stroker M20 engines and sell the parts to build them too! ;)

I've heard they're kinda cool. Only kinda.

[Mike36]

Anyone have a built stroker motor that I could put in my 1988 325iS. Not looking to spend the $/time sourcing all the parts. Saw a 3.1 Stroker built ready to go on the FB forums in the summer for a very good price, sold immediately and still kicking myself. Just wanted to see what's out there

I believe e30streetsweeper on IG is selling his stoker M20. He has it in his LTO wagon widebody.

[TobyB]

I have wondered about upgrading air flow on the M20. Many have said that the stock airbox performance cannot be improved with a cone air filter.

for a total n00b (me) — what does it take to increase the intake & exhaust manifolds? Just curious.

Throw them in Digger's bin.

The AFM is the first restrictor, followed by the intake manifold (if you're r3vving it high enough to matter) and then the whole exhaust system is the next bottleneck...

ITBs and straight pipes out the hood ftw. THEN some port work starts to make real sense...

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