so i have a 2013 L20 4.8L that ate a cam on intake #3 and was doing some reading that you can put the pistons from a 4.8 into a 5.3 and it would bump the compression up. but all the posts i seen reference the old 4.8L's with the flat top pistons where as the pistons i have have the valve relieves in them. anyone know if this is still doable? as i have an old 5.3L laying around that i can take the rotating assembly out of and mash the two together. and also would anyone know roughly what the compression ratio would be at

 

The comp bump in the later motors comes from swapping out the 799s

After... 07, ish? All 5.3/4.8 had the same pistons

where are you located? By chance 😇

 

2007-2009 motors did not have VVT. 2010- motors had VVT with notches in the pistons. The compression in the early 5.3s was 9.95:1 and the VVT motors it was 9.6:1. Early motors ran a single pattern camshaft, later ones dual pattern. No need to swap pistons, they run the same part number where compatible.

 

and for clarification, 'early' in this instance means early Gen4 engines.
the Gen3 5.3s were either 9.4 or 9.6 SCR because they had dished pistons. and that was with the tiny 862/706 heads. once they all went to flat-top pistons, they changed to 243/799 heads to maintain CR.

 

The Gen3 Factory 5.3 with dish and a 706/862 was about 9.5:1
When you add flat tops it increased to around 1 full point around 10.5:1

But if you use a 243/799 with a flat top in a 5.3L it goes to around 9.9:1 Like an L33 where it was done from the factory but with an aluminum block

 

after reading my post again, i can see where the last couple words might be misleading (because the bigger heads didn't drop compression all the way back down), but otherwise, that's the same as what i just said.

 

My research shows all 07-13 4.8Ls use the same part# cam. I had assumed that when the 4.8L added VVT that GM would have used a different cam but I'm pretty sure it is the same part # 07-13. I tune for an engine shop that uses the 4.8L cam when they do DOD deletes on 5.3s and want to retain VVT with a stock GM cam. Can you provide GM cam part #s for the different 4.8L cams you say were used?

 

The LY2 camshaft is 12625437 and it was also used in the LMF, LH8 and LH9, all 5.3 motors without VVT. This grind is smaller than the VVT camshaft used in the LC9 and LMG and smaller than the single pattern cam used in the 2007-2009 LY5, LC9 and LMG.

If memory serves the grind for the L20 is the same with the addition of VVT, don't have the part number in my list for some reason. Took another look, that 5437 cam is listed as VVT also. It's been a few years since I made the list, memory fading on the details. Might be worth a look at Nutter's LS engine data over at Summit Racing.

 

I think I've also seen some differentiation in the power ratings on the GMT900 5.3 and 4.8. Although I thought all the GMT900s were all certified to SAE J1349, but maybe not. You used to be able to go to the GM media website and download all the what's new marketing info for each year model and they would also have all the dyno graphs available. Then GM turned into a bunch of do-gooders and are going to supposedly save the world by banning combustion power and now the only thing you can find on the GM Media website is a bunch of corporate BS about how climate change is real haha.

You can still look at the old versions of the page through wayback machine but it only works about 10% of the time for whatever reason.