On a 325ci, 5.3L with 9:5.1 compression pistons, what would LS1 heads drop the compression to? This would be using stock height head gaskets and we'll just say no milling. I might mill slightly to straighten out the deck.

 

I know, the other way around, the 5.3 head on a 5.7 motor will increase the comp to around a point higher. So I would imagine the same in drop though? Don't you think?

 

yea i think your right.
damn,

 

Yea I have been debating on wether to put mine on though.
I heard that they will work if you take them to the machine shop and have them weld so they combustion chambers are the same size.

 

yea but you could just get head work done to the 5.3's since they already come with a smaller chamber size. it seems my compression would drop to near 8:5, which is way to low for only temporarily nitrous use.

 

Yea im still wondering if its worth it. You do get bigger vavles. But I dont think It would drop that much compression if they welded the combustion chambers the same bore as the block. My buddy is putting LS6 stage 2 heads on his truck. They had to weld the heads to match the bore. I dont think it will drop compression that much.
What do you all think ?

 

It will drop the compression if you put 5.7 heads on. It would cost a **** load to have the combustion chambers welded up to raise the compression. Just hang out in the parts for sale section, not truck section and look for a set of 5.3 built up heads. That is a big thing for ls1 guys to do. Most machine shops take the 5.3 heads and port them, and put bigger valves in them and get great numbers out of them. You can normally find a set for a reasonable price too, used of course, some new though.