Jake75

iTrader: (2)

True, I had mine milled .010

madmann26

iTrader: (7)

Why 243's? With milling it's going to rise the compression ratio and for a boost motor you don't want the compression ratio to high.

IMO - 317's would be better, cheaper and flow just as well as the 243 head.

marineusmc4

I was gonna have them milled to bring compression back to 9.5:1. Do you know what the compression is on them if I don't mill them?

marineusmc4

To raise compression. And to be flat lol

madmann26

iTrader: (7)

What motor are you putting these on? The 243's have a small chamber and would bump your compression up as they sit. The 317's are the same head but with a 71cc combustion chamber, thus why they are preferred for boosted app's.

Gbrown1320

iTrader: (6)

compression with a stock LQ4 and 317's is 9.5:1. If you swap the smaller chambered 243 heads onto the stock LQ4 you're looking at roughly 10.4:1, and that's without milling them at all.

madmann26

iTrader: (7)

Exactly my point.

With 9.5cr, you're DCR (dynamic compression ratio) will be 15-16cr (this is good).

Treat DCR as how fast does it rev when you blip the throttle. With a pd blower, it's going to feel really really snappy.

marineusmc4

These 243s will be going on a 5.3 motor not a 6.0

marineusmc4

And I was wanting to keep the stock compression roughly the same in case I ever decide to take the blower off and go N/A again is all.

madmann26

iTrader: (7)

With this combo and .030 milling, .051 headgaskets, your CR will be around 9.5:1.

You loose compression from the 5.3 to the 243 heads because the 243 has a larger combustion chamber.

The 5.3 head has the smallest combustion chamber of any stock ls type head.