Pistons for m20 Stroker

[digger]

Yeah a couple years back they didn't off that skirt style in both alloys

[zaq123]

This is a piston that TopEnd designed for my engine build (E36 2.8L crankshaft and rods, 885 head,CR 10.7:1, Schrick 280/272 camshaft) using the 4032 forging

what size is it? 85mm? looks like IE/Mahle one

[cdeason7]

Yes 85mm

[bmwmaster81]

This is a piston that TopEnd designed for my engine build (E36 2.8L crankshaft and rods, 885 head,CR 10.7:1, Schrick 280/272 camshaft) using the 4032 forging

Could maybe someone post also a photo of the mahle motorsports piston?

The dome and dish somehow looks much more flat than the one on your pic.

Now you reach wirh yours 10.7:1 CR......
Mahle targets 10:1 CR.....

But now im asking me how thick is the squish area on the mahle pistons? And how good does it fit to 885 head? Is the angle of the dome in squish area paralell to the chambers squish ?
This is an importand factor to use this type of piston.
Which piston has now the better shape ;D?

[cdeason7]

I am sure Digger or SkiFree can give a more technical answer to your question, the dome on the JE pistons is very similar to the stock M20 piston, the CR is dependent on the gas that you will use and the camshaft that you will use plus other variables, the IE/Mahle piston is speced for 91 octane gas, you have much better gas in Germany (97 octane Shell for example) than we get in the US, I would use a CR of at least 11:1 dependent on your build

[digger]

Topend would have gotten the stock Pistons scanned. For this reason they don't seem to modify except to extrapolate to large bore and valve reliefs.

I presume Andrew did the same when he was at IE working with Mahle ms. It's likely the dish is modified a bit to arrive at 10:1 but that's me making an assumption

It's probably just the dull grafal texture that changes how it looks

[SkiFree]

When working with the engineer at Mahle, I sent in a sectioned 885 cylinder head to be scanned, along with the piston. Since he's with Mahle, he was actually able to pull up the original OEM drawings and use them as the base when drawing these.

Also specced for this specific piston was the 284/280 cam. And yes, the system was setup for 91 octane.

Here's a couple old comparison pictures. You can see how the cnc milling on the MahleMS results in the mirroring of the stock dish angles, while using the blank forging you can get close, but not quite the same.

[digger]

What is the cc of the done and CH ?

[ForcedFirebird]

This is a piston that TopEnd designed for my engine build (E36 2.8L crankshaft and rods, 885 head,CR 10.7:1, Schrick 280/272 camshaft) using the 4032 forging

Can't wait for numbers on this. Your head out-flowed the previous local head that made good power, but needed more cam than the 272/272 used (even with 9.5:1). Curious to see if that cam/combo also runs out of steam....

[dustyperez]

Why not use cp pistons? They are what i have with the 89.6 crank and 135 rods. They were the first custom I believe for that crank and have the dimensions on file. I just gave them bore, stroke and rod length. they did the rest. It was about $1200 but they are pretty.

[digger]

Do they have the proper dome on file ? If not you need to send a sample.

Cp are every bit as good if not bettter the JE in a general sense this is based on professional opinion I've been told from people who have been getting stuff made by both companies and others

[digger]

any CAD guys wanting design their own piston dome

this is how the m20 8.8:1 style piston dome seems to be made

spherical dome (not a hemisphere) approx R100





subtract a spherical dish approx R80mm

the centre of the sphere is offset in two directions from the bore axis (towards the spark plug) as well as being offset in the piston axial direction






section view showing dish (9.7:1 style pistons have bigger radius making a shallower dish)



SO in actual fact the squish is not a chamfer its slightly radiused. Same with the head the machined part is radiused (concave) to match the piston



if you look at the spark plug side the head there is a decent amount of potential area for squish, however the OEM pistons dont utilize much of it as possible because its removed when the dish is added. you could design a custom higher compression set of pistons to use more of the area if you wanted...

add some valve reliefs



get a sample 3d printed and mock it up to check you didnt fuck it up...

[ForcedFirebird]

Now it makes sense!!!

Drei Kugel wirbelkammer is what they called the m20b25 design, which loosely translates to "Three ball turbulence chamber". The piston is one ball, chamber is another, then the dish is the third ball.

[LateFan]

which loosely translates to "Three ball turbulence chamber"

Funny but logical!

I've had bad luck with these - I think it's that the nose keeps digging in to the cyl wall...I wouldn't recommend them..

[bmwmaster81]

I have got laser scan *.stl files from m20 pistons and amc head. Sadly with *.stl files its not possible to construct something. When soemone is interrested and can convert stl in to something useful for cad, please pm me.

https://drive.google.com/open?id=0B73WY9YlBFqRVWdMVHVrLUNtMDA