I am currently putting a 6.0L LQ4 in my 98 T/A, ths is a budget build for right now to get the car running, the engine will be coming back out hopefully this winter to be stroked to a 408.

Anyway I have a set of stock 5.7L heads [casting 853] deburred and milled .060 [this was done to reach 10.5:1 compression, since this engine had the dished pistons in it.

Also I have a set of 4.8L heads [casting 862] that the combustion chamber has been deburred. Now from what I have been told/ read that these 4.8L heads are the exact same as the 5.3L heads, as far as valve size and everything.

As far as a cam I am running a 236/242 612/622 @ .112, LS6 intake, Hooker LT's into an Xpipe.

It is an automatic car, 3800 Vigalantie stall, and a 3.73 gear in the back.

I really appreciate and help you guys give, I just want my car running for now so I can enjoyit a lil, but since I have these 2 options I want to know what will help me out hte most powerwise.

 

the 4.8's won't perform very well until they are ported. the 5.7's have better port flow and will be the better choice.

 

Well yeah, aside from the fact that you are wrong. The 5.3 runners are the same. The only difference is the combustion chamber and the smaller intake valve size 1.89" compared to 2.00". As is the 5.3 will actually flow better than the 5.7 head. When you will a head that far it crushes the flow path and can inhibit flow through the range. Besides that a mill of .060 is pretty extreme and doesnt yield 10.5:1, its actually closer to 11.2:1. That would be with a 3.905" bore. You are talking about a 4.00" bore and that just ups the compression another .2 or so. Either head is going to have you at or over 11:1 depending on gasket thickness(assumed stock pistons)

Brandon

 

These are stock pistons, I am using GM factory head gaskets. Now as far as the pistons they are stock but they are dished and from what I know/have seen the 5.7L LS1 has a flat top piston.

 

So the engine is a 5.7 or 6.0?

 

Sorry its a 6.0, but the heads were milled to compensate for the dish in the piston on the 6.0L. I was just going by what the machine shop told me.