3.0 stroker theory

[whodwho]

Looks like CR would be ~10.5 depending on if the head has been surfaced and what is done with piston reshaping

http://www.zealautowerks.com/advanced-compression-calculator.html?setup=6,m84.00,m206.00,m86.00,40.00,0,m28.32,m135.00,i0.070,m0.000,7200,1500,0

Here is another calculator I stumble across but haven't used yet, a bit more parameters to play with to see effects on valve timing by head skims/head gasket thickness

http://www.not2fast.com/turbo/compression/compression.shtml

[E46Twist]

Good find! My thoughts for the pistons would be to measure clearance in stock form and then skim then down .12mm if there was contact. I am only 2 hours from MM so I could always see what they would charge to cut reliefs.

"Fast is Sexy"

[E46Twist]

So if all goes well I should be able to get most of the stuff to build the stroker from a forum member. I will just need pistons.

[e30 gangsta]

Why not do m52 crank, 135mm rods, and custom +2 mm overbore pistons? Youll save a lot of money on macchine work alone.

[digger]

i would use a piston (stock, aftermarket or other) that preserves the combustion chamber dynamics of the OEM pistons. a taller comp height piston with thick crown would probably suit better though more material would need to be removed but could be shaped better. or use a shorter rod, b25 piston and M/C crank. or shell out 800 for forged babies. lots of options

[E46Twist]

The purpose is to explore and see if the M54 pistons will work, and there is a decent chance they will. If they do you can build a 2.9 pretty cheap

"Fast is Sexy"

[redlightpete]

The purpose is to explore and see if the M54 pistons will work, and there is a decent chance they will. If they do you can build a 2.9 pretty cheap

"Fast is Sexy"

Have you looked at b25 pistons? If you don't replicate that shape, you'll end up with a kind of haphazard combustion chamber. I guess you'll find out if it works out ok or not. Please keep us updated.

[E46Twist]

I do expect to need to shave the reliefs off

"Fast is Sexy"

[Bullet Ride]

The purpose is to explore and see if the M54 pistons will work, and there is a decent chance they will. If they do you can build a 2.9 pretty cheap

"Fast is Sexy"

You can make the M54 pistons work but it will likely be cheaper just to order a custom set of pistons rather than paying someone to machine M54 pistons to match the combustion chamber of the 885 head and they'll end up looking like this...

[E46Twist]

As soon as someone can show me a case of using this setup and it not working or getting to be $$$ I'll stop it. I know the M54 pistons are not optimal in stock form but if they work with a stick or slightly thicker HG then I count it as a success. The 2.7i stroker is not perfect but runs on the principle of cheap yet effective and worth while. I am not doing this to get a the most power I can, I am doing it to justify not doing a turbo or swap. If it fails I can shave the pistons myself but would not consider a successful budget stroker.

"Fast is Sexy"

[digger]

A flat top style piston still works with an 885 head, infact many aftermarket pistons aren’t the OEM shape so it is not a show stopper by any means.

It’s not what I’d do as less squish and subsequently less mixture motion is not good for an efficient burn. The M20 can make as much if not more torque per litre as the 24V versions when done correctly it just has a harder time breathing.....

As for how important piston shape is, well BMW designed atleast 4 different piston crown variations to be used with the 885 with all being basically the same offset dish-dome and angled squish. Three were for the b25 in varying CR and one for the SETA so they thought it was important.

from what i have noticed over the last decade those with good CR using OEM shape piston and the 885 make better bottom end and midrange which IMO is down to combustion efficiency. i dont have scientific proof but it seems to be the trend. those with flat tops often tend to be trickier to tune due to knock if CR is up there and cam duration is relatively small.

flat top suits a 200 or 731 head