piston options for m50

[meanEG]

Just thinking of rebuilding an m50. Not looking for crazy power, just a little more compression. just trying to get 11:1-11:5. just conservative enough to run a chip instead of standalone.

I would like to know if anyone has measured the n52 pistons to see if the piston pit height. I dont want forged pistons, so stock bmw pistons will be fine. boring is fine. i read about he m50 pistons in an m52, but i need the opposite. i dont want to buy a crank and stroke it either.

[techno550]

stock ecu vs standalone won't make a difference. Stock ECU (even obd1) does a better job of knock control than most low end aftermarket ecus.
You are better off looking for more displacement than higher compression, especially given the modest gains raising the CR will give you.

Its already 10.5. Refresh with stock pistons, deck the block, and deck the head.

Also note that there is no guarantee that it'll work with pump gas if you go too far CR wise.

[meanEG]

i had success running over 12:1 with standalone, but any real gains with displacement isnt practical. i do not want to buy a new crank. i will freshen up with new .5mm over pistons, or the 86mm ones form bmw.

i was just checking to see if i can get BMW slugs instead of forged. just getting my ducks in a row, prior to doing an engine build. i am picking up a m50 for really cheap andi was going to do the head over. while apart, if i find no hash or scores, than i will do a fresh bore on the bottom end.

[techno550]

12:1 on what motor? every motor is different. Combustion chamber shape, cams, cooling, etc all play a role in making it work.

S52 cranks are ~$350
BMW pistons are very expensive new.
Used BMW pistons can be found, but ring sets for anything other than 84mm is expensive.
S52 rings are over $100 per cylinder
M50/M52 rings are under $50 per cylinder.

If you are going to spend $700+ putting new rings on old stock pistons, why not spend a hundred or two more and get a set of pistons.

and keeping the 2.5 crank makes no sense to me.
You would be better off getting a junkyard 2.8 and refreshing that instead. still cheap parts (same bearings, rings, etc as the 2.5), and deck the head and block a bunch.

[meanEG]

i feel you on the 2.8, just trying to work with what i have. i need to get back home and check worldpac and imc for overbore options. i ahvent priced priced piston yet for any motor except used bmw pistons. just seeing what will work for now if anyone has tried and found one that will yield a little higher compression.

i know that every engine is diffeent, but it was a 4 valve hemi head, with custom pistons. it was a h22 prelude engine. dont flame for being a honda, i know its not a bmw.

[Wanganstyle]

Get a junk 2.8 or junk 3.0 or 3.2 instead of the junk 2.5 you want to start with; or keep the 2.5 and turbocharge it.

"Building" junk style for a bmw engine is a waste of time; keep stock computer and don't Fuck with it.

Pretend building is also a waste of time for a Honda as better newer Honda engines can be purchased legitimately unlike the majority of H onda crowd enjoys.

Bigger always wins; you can keep the 84mm bore and stroke to 3000cc with a simple crankshaft change.

Or just 3200cc and call it a day; maps are available from TRM and others.

3200cc > whatever pretend modding claims with a 2500cc

[richard.bratton]

12:1 on what motor? every motor is different. Combustion chamber shape, cams, cooling, etc all play a role in making it work.

S52 cranks are ~$350
BMW pistons are very expensive new.
Used BMW pistons can be found, but ring sets for anything other than 84mm is expensive.
S52 rings are over $100 per cylinder
M50/M52 rings are under $50 per cylinder.

If you are going to spend $700+ putting new rings on old stock pistons, why not spend a hundred or two more and get a set of pistons.

and keeping the 2.5 crank makes no sense to me.
You would be better off getting a junkyard 2.8 and refreshing that instead. still cheap parts (same bearings, rings, etc as the 2.5), and deck the head and block a bunch.

You can buy custom moly rings for any BMW six for around $220 if you know who to call...

[meanEG]

Get a junk 2.8 or junk 3.0 or 3.2 instead of the junk 2.5 you want to start with; or keep the 2.5 and turbocharge it.

"Building" junk style for a bmw engine is a waste of time; keep stock computer and don't Fuck with it.

Pretend building is also a waste of time for a Honda as better newer Honda engines can be purchased legitimately unlike the majority of H onda crowd enjoys.

Bigger always wins; you can keep the 84mm bore and stroke to 3000cc with a simple crankshaft change.

Or just 3200cc and call it a day; maps are available from TRM and others.

3200cc > whatever pretend modding claims with a 2500cc

I understand what your saying. I am not going to do a junk build. I want to bore if I am going to freshen up an engine. That is why I am looking for 86mm piston. I am hoping once I get out opened up I still have crosshatch and I don't have to fuck with it.

[Wanganstyle]

I understand what your saying. I am not going to do a junk build. I want to bore if I am going to freshen up an engine. That is why I am looking for 86mm piston. I am hoping once I get out opened up I still have crosshatch and I don't have to fuck with it.

Don't bother If engine has not been abused
The pistons don't wear; bores either.

Stock 3200cc uses 86.4mm pistons.

It doesn't matter what increase bore or what compression pistons; 2500cc vs stock 3200cc is loose all day

to give prospective:

2500 cc @ whatever compression and whatever bore (lets assume its magically 2600cc) = probably 175rwhp at best best
2800cc is ~175rwhp out of the box with ~ 185 torque to the ground
2800cc + M3 stock cams is about 200rwhp and torque
3200cc is ~215 hp and torque @ the wheels. All stock passes cali smog 240k miles

If you are making a sleeper street racing engine the 3.2 looks identical to a 2.5 including head casting number.

All the 24v blocks just take bigger stroke cranks and bigger bores

If you want China pistons then there are Maxsil available in double overbore.

If tying to make weird engine out of scraps then the "A A " 2.9 is the one to follow. It's putting higher top pistons and over stroking a little.

Realistically pointless as a s52b32 is a set of pistons for the same price and also avail in double overbore.

If you want to punch it past 84 then why not 86.4 or 87.0?

If worried about bore size just O ring it and run Arp studs on stock hg; works for the turbo guys.

Just trying to help you spend unneeded money and trouble at this point.