Alright so I am getting a ls1 shortblock, its going to replace my old tired 5.3 eventually when it decides its had all it can handle or I just get bored one day. Is there any adverse performance effects to taking the heads off my 5.3 to run on the ls1, its out of an 04 GTO. I know the intake valve is smaller but i have heard they flow about the same and I know the chambers are a little smaller on the 5.3s too so up goes the comp ratio. I just want to keep it all budget, getting one hell of a deal on the shortblock and dont really want to dish out more money for heads since i will have a pretty much worthless 5.3 that will probably make a trip to the scrap yard after i take it out.

Jon

 

I would like to know this also. bump

 

Not worth it unless you go with bigger valves and port.... They don't flow stock with an untouched 853 or 241 casting.

 

You can buy low mile 853's or 241's for $100 all day, that's what I would do.

 

i see hear this alot...but here are the facts....both heads flow damn near the same...and you get a nice bump in compression...ive ran the 5.3s but they were hand ported and yes with the smaller valve...idk how much power i gained but the car was alot tourqier all through the powerband than it was with the 806 castings...

 

The 5.3 heads flow almost identical to the LS1 head. The smaller valve doesn't hurt them much at all. There is a flow sheet that I just reposted that compares the LS1, LS6, 6.0, & 5.3 stock heads. At .600 lift on the intake the LS1 flows 227 and the 5.3 is at 226. The numbers are within a couple CFM thru the entire lift range.