Eventually I am going to build a 5.3 to take the place of my 4.8. However instead of just rebuilding a regular 5.3, I wanted to use flat pistons from a 4.8 for higher compression. At first I would have stock heads, but eventually a set of the PRC's will be purchased.

My question is this: stock compression is 9.5:1 right? Flat-top pistons will raise it to 10:1 correct?

Finally Texas Speed says the heads are designed to raise compression to 10.75:1...with the flat tops this would raise it to over 11:1... can you run this with pump gas? If not, how would one go about lowering the compression while still using the flat tops?

OR is all my math wrong...help me

 

I'm sure you can run 11:1 with pump gas as long as you use 93. Thicker head gaskets will drop it some too, I think a lot of duration will bleed off some too

 

11:1 or even 11:5 would be fine with pump gas ( 93 octane ) theres a few i know who runs 12:1 without issues on pump gas even 12:5

 

Can someone verify my math for me while they're at it? I'd be using stock GM gaskets if running that high compression would work out.

 

That info from texas speed is raising compressiom on a ls-1 not a 5.3. I had the same question when purchasing my heads.

 

Hmm, well why label them as 5.3 heads.

So....someone have any ideas on what compression would be on a flat top 5.3

 

4.8 pistons in a 5.3 with the stock MLS gasket and the stock 706/862 heads is almost right at 10.3:1 CR. If that helps ya...so if the PRCs are milled any then compression will go up from there... I have this same combo and am about to switch to 243's so i can go down to around 9.9:1 for FI

 

They are labeled 5.3 heads because they are 862 castings from a 5.3. That quote is if you put these heads on a 5.7.

 

Exactly! Sorry for the confusion everyone!