Pistons for m20 Stroker

[digger]

What is the cc of the done and CH ?

[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]

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

[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

[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]

Yes 85mm

[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

[digger]

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

[cdeason7]

A few months, JE, my engine builder prefers working with JE,
Design look ok ?

[digger]

How recent ? je or cp ?

[cdeason7]

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

[digger]

If you're not using a huge cam there is no reason you can't avoid an oil rail with 135 rod and 89.6mm crank you use a 20mm pin ( rebush rods) the land and ring sizes add up last time I checked but you need to talk to the manufacturer

[digger]

If you want the same features then make sure you ask for the slipper-skirt design, the coatings, and be sure the dish is the correct offset (the blank that JE and others sometime use is slightly off). Just be best to ask for a photo before committing.

Je don't do a slipper design in 4032 dont have forgings but it's not big deal. Off set pin is a good idea to help keep things a bit quieter (pretty sure the mm were offset) or conversely reduce friction on an all out motor done by reverse offset.

[zaq123]

Interesting on a all-around use design.

And are you saying (#1) the rod could swing far enough that it might hit the skirt where the ring land is? I'm not understanding that - isn't the bottom land always above the wrist pin bore? Or are you saying (#2) the pin diameter is getting larger and encroaching on the bottom land?

...still trying to see this in my head...or is it (#3) the actual pin location is changing relative to the top of the piston depending on stroke and CR?

oil ring falls into the wrist pin bore area hence the need for the support rail...results of piston's short comp. distance. Cons of this design is very debatable

[LateFan]

It is much easier to make a big-number race piston than a well-rounded efficient street-focused power piston. With larger strokes the wrist pin begins to encroach on the lower oil-control ring of a healthily-specced ring package, necessitating an support ring.

Interesting on a all-around use design.

And are you saying (#1) the rod could swing far enough that it might hit the skirt where the ring land is? I'm not understanding that - isn't the bottom land always above the wrist pin bore? Or are you saying (#2) the pin diameter is getting larger and encroaching on the bottom land?

...still trying to see this in my head...or is it (#3) the actual pin location is changing relative to the top of the piston depending on stroke and CR?