miata2fast

iTrader: (2)

I just pulled apart a high mileage spare motor I had, and I looked at the piston and compared it to the pics you posted. You can clearly see that your pistons have had all of the sharp edges worn off, and all the machining marks on the surface are gone. Also, it almost looks like the metal is porous from all the little speckeling on the surface.

Did you have the piston surface modified? If not, it would be a continued low level detonation that caused it.

On the pistons that I pulled, there are machine marks on the surface that are visable. Also, there is not that pot marked appearance like on yours.

I will get a pic of the piston for you to compare.

Doppelgänger

iTrader: (12)

That would be appreciated
Considering this was 2.5 years (and enough miles) of daily driving, track days, punded on 12+psi, run hot a few times, run with dead WB02, very rich at times, autocrossed and generally abused....I don't think it looks all that bad.

miata2fast

iTrader: (2)

They don't live forever.

Doppelgänger

iTrader: (12)

FYI- Here is a picture of a brand new 1.8 piston from the factory. You can tell be the machined spot at the center of the poston, that mine is not pitted. So it seems there wasn't any severe detonation other than the spots on #3 and #4 by the exhaust valve. Although no detonation is "good", mine was by no means severe nor catastrophic.

miata2fast

iTrader: (2)

That is interesting. They must have changed piston manufacturer or build method. The 99 piston I just pulled and cleaned (I was meaning to get a pic) has machining marks on the top, with only the valve reliefs with casting flash.

Edit: The machined button in the center of the piston should have been a clue to me that the pits were normal.