I bought these pistons earlier this year and have completed the engine, which runs great. In trying to figure out the compression ratio, I am unable to find any information on these pistons. They are installed in a 2005 Gen IV LS2.

Some of the marking on the top are:
K13 FM
81133A
12598942BA or 125989428A
R-2043

any help would be great!

Thanks in advance
-Aaron

 

Where did you get those? I've never seen a piston designed quite like that.

 

I found them on eBay from a guy who described them as "removed from a motor with zero miles". His exact description was "LS2 LFA LY6 L76 PISTONS, RODS, RINGS, BEARINGS 6.0 Litre". When I received them they were nothing less than brand new. Funny thing is I cannot reference the 125# anywhere, wonder if they are a GM experiment.

 

those look like the new direct injection pistons, i bet those were setup in a 6.0L prototype or test motor