930 Mahle piston orientation

[JFairman]

I'm going to install some 911 turbo pistons into the cylinders and I'm not sure which way goes toward the flywheel. I know the piston pins are offset and not centered so it's important to get them right.

There is a little symbol towards one side in the top of these Mahle pistons and I'm including a picture of the top of one of the pistons.

Does this symbol in the right side of this piston dome mean the piston should be installed so it points towards the flywheel?

Thanks in advance for the help.

[Walt Fricke]

This is one of life's mysteries. With VWs we all knew the deal. Marks (arrows, actually) toward the flywheel on both banks. That was the stock method for anti-slap. For power (like Formula V), point the other way. This worked because the domes were symmetrical.

Now we have 911 pistons, most of which have various allowances for valves - intakes are bigger, and often open farther. Or swirl tops like the CIS. Some have wrist pin offset, some don't. The 2.7 CIS pistons I had have no marks, and for certain don't have right side pistons and left side pistons, which is what you need to do this offset thing with asymmetric domes. Yet they had wrist pin offset. So one side was anti-slap, and the other side would push a little bit harder.

But your turbo domes look symmetrical, so this can work and if you don't find some factory guidance, I'd say put the mark toward the flywheel on both banks and be happy.

Or the other way around if you are trying to coax out the absolute maximum HP - which I'd guess is not the plan with a turbo where you can more easily just figure out how to live with a little more boost?

[infraredcalvin]

IIRC the symbol you mention is a symbol showing the crank and the flywheel. So in this picture with the number 5 facing right side up, the motor flywheel would be to the right.

[Ronnie's.930]

Jim, when I disassembled my engine several years ago, the pistons were oriented as you noted in your post (the side of the pistons with the symbol faced the flywheel). I assumed that the symbol is supposed to represent the crank and flywheel.

[infraredcalvin]

No image, but a bit of reference to crank flywheel image...screenshot from webpage (under installation direction):

[Flat6pac]

The squiggle points toward the flywheel.
Bruce

[JFairman]

Thanks everybody!
Thats what I thought