How To Choose The Correct Piston Material
 

Which Aluminum Forged Piston Is Right For Your Engine?

A frame of reference for you...I have built 3 twin turbo M28 engines from the block up with the 2618 piston set from JE running on Nikasil plated bores. All three engines were set to 0.0025" piston to wall and to the best of my knowledge all three are still running very well. If you sleeve it, the clearance woudl have to be like 0.004"-0.005"

As important to strength as piston material is, so is the design...for example the ring lands on the 928S4 pistons are quite a bit thicker than on the 4.5 liter engines...so in that case you can run more boost with all other factors equal. I've seen many boosted 928 engines suffer ring land failure, mainly the early cars but this usually stemmed from improper ignition tuning...it is so often neglected when people go live with manifold pressure. Also blown head gaskets...so often these problems can be totally avoided simply by backing down the ignition 1 to 1.5 degrees per psig of boost.

Hard to say on Mahle's mix...there are a lot of closely guarded secrets in that realm.

No doubt if you don't need the strength and ductility the harder piston will outlast the softer piston. There are so many variables at play.