In what way, machining, finish or shape?
Pretty much everything.
This is as close to an apples-to-apples as I can get:
A FBF 88mm hi-comp, pretty sure it's a Wiseco on the left, vs. a Mahle 91mm on the right.
Mahle is 3mm larger, yet only 12g heavier with the pin.
FBF is naked aluminum, but Mahle piston is coated everywhere, and has some sort of other coating on the skirt.
FBF is pretty chunky, while the Mahle is pocketed above and outboard of the pin, and the pin bosses are contoured.
Mahle has a shorter pin, with a tapered bore.
Mahle crown and dome fit the combustion chamber better, so end up with a more efficient squish.
Neither piston fits the chamber all that well, which annoys me greatly.
The cost of doing it properly is minimal.
As an example, the squish area of the FBF is totally flat.
The mating chamber area is domed slightly.
So the squish is limited by the very edge of the piston, and gets wider as you go toward centerline.
So it's squandering compression.
Not a deal-breaker, but fixing it is troublesome.
It's not a totally fair comparison, as the Mahle are likely 2X the price of the FBF.
And in a street motor application, likely not much benefit.
It's just annoying that they both could have done the crown properly for maybe $10 more in machining and design per piston.
And it'll cost far more than 10X that to fix it even halfway.
