I'm trying to identify these pistons. I'm told these are factory GM 5.3s (3.78 diameter). I don't think factory 5.3 pistons have valve reliefs, right? I've searched for the numbers printed on these with no luck. These sit .010 above the deck (on what is supposed to be a new block). Is that typical for factory pistons? Thanks for the help!

 

All LS motors come out of the hole ~.01, its part of their design. It was something GM bragged about in literature as well

They look like hypereutectics, based on the cast in; rather than machined in valve reliefs.

I can do some more looking when I get home, but I feel that they are likely LS1 pistons. Can you get an OD measurement?

 

I get 3.750 (measuring at the crown - can't get to the skirt), which would be about right for the stock bore. I have factory LS1 pistons in my garage and they don't have valve reliefs either.

Agree on the hypereutectic comment.

I was planning on running .040 Cometic gaskets w/243 heads, but I think I need to stick with stock gaskets considering that they're .010 out of the hole.

Thanks for the input! If you manage to track down more info, I'd appreciate it but at this point, I guess it's not that important. I've got the info I need.

 

LY6 pistons have factory reliefs but to my knowledge none of the stock 5.3 pistons ever did.

Pull one out, maybe a brand is stamped on it somewhere.

 

IIRC the VVT motors have a valve relief. Could be wrong... It happens

 

My 5.3 LC9 motor with VVT is just a regular flat top piston. I believe the LMG motors are the same.

 

LY6 is a 4.00 bore with LS3 reliefs.

Ill do some more digging now that I know there are stock bore

 

Possibly not a LS piston? The opposing valve reliefs suggest a four cylinder application with offset valve angles. The Ford 2.3L has a 3.78 bore, may start there with a search.