Flat top pistons came in the l33 engines which was on the. 05 Ecsb z71 and in all the nnbs 5.3s..

 

.030 with a .40 thickness gasket will put you at 9.9:1

.030 with a stock .051 gasket would put you back to roughly 9.5:1

this is for dished pistons.

 

What heads came on the L33?

 

799s... that's what my 5.3 has...

 

Ok, you can treat them like the NNBS 5.3's then.

OP : if you have the L33... you don't need to mill your heads at all.

 

Yea, the aluminum 5.3 HO's had flat tops, and were available in 05. That's the engine that Bill (trever1t) has in his hot rod. Not sure what other years that they offered that engine, but I know that it was a short run

 

The block would look like aluminum and not rusted metal.... Bright colored bare metal.

 

The block will be aluminum colored and the pistons will be flat tops. Check the RPO sticker in your glove box for L33, if you see that, you have the aluminum block, if you find LM7, you have the iron block with dished pistons like most of us, myself included

 

Here is a picture of my 05 L33... Also you could try to see a magnet would stick to the block as it shouldn't stick to aluminum.

 

Or just check the casting on ur heads... l33 only came on. 05 ecsb z71 package 5.3.. called the 5.3 HO.. has casting 799 on the heads.. anything else means u have iron block