I'm trying to figure out what I have before engine upgrades in a year or so. This engine came to me as rebuilt. I removed the #1 cylinder plug and used a cheap usb endoscope to peek inside. The pictures I was able to take aren't great (the live feed was much better) - the piston was near TDC so every picture is a closeup.

It looks to be a standard deep dish (good on pizza, not so much on engines) piston. There appear to be markings that would confirm exactly what they are, can anybody make them out?

Also, I expected the piston top to be dry/clean - this looks like it has a fair amount of oil/sludge inside. This isn't normal, is it?

 

Looks like 332AP - huge dish. Refer to other posts on this forum for opinions/options.

https://www.summitracing.com/parts/stl-332ap

 

Yes, I thought I read 332AP as well before reading v8al's post.

Pertinent specs from the Summit link above:

1. Compression Height (in):1.596 in.
2. Recessed piston head is 0.215 inch deep x 2.920 inch diameter.

#1 is about .020" shorter than a factory piston, which means the compression ratio would be less than a factory piston with a comparable size dish.
#2 calculates to 1.44 cubic inches or 24cc, which are the HUGE dish 1971-1972 pistons that give maybe 8.5:1 compression ratio with the factory compression height.

So with the short compression height, HUGE dishes, 68cc combustion chambers, aftermarket composition head gaskets, and unmilled block deck, the compression ratio is around 7.6:1.

 

That sucks, but isn't really shocking. Thanks for helping confirm. Any comments on the appearance of the pistons?

 

I'm not used to seeing such a rough finish, on the pistons I had to work with. Is that normal?
Just for extra measure, I'd examine the other 7 specimens, as well. Being a rebuild, you never know if it ended up a parts shelf grab bag