I'm going to be building a 5.7L LS1 motor and have noticed that many f-body guys have put 5.3L truck heads on their cars. What are the gains of this, more hp., increased compression ratio? What hp gains are seen with this?

 

5.3 heads on a 5.7 bump compression to around 11:1 I think. I don't know what the limits of 93 octane or how much timing you can run vs detonation due to the quench of the heads, chamber design, etc

 

Yes a ported 5.3 head can out flow a ls1 head and has a smaller combustion chamber, so the heads don't have to be decked...in alot of ways it's a poor mans ls6 head.
TEA stage 2's are awesome 5.3 heads.

 

I dont think the 5.3 out flows the 5.7, people use them because they flow very well (as do the ls1's) But they also bring CR up to 11.1 as stated before and with a mild mill, they bump to 11.3, so with that and the right tune you can make power, as well with race gas and N2O, look out!!(if the right cam is installed)