after repeated searches and literally days of searching the internet i CANNOT find a solid answer. i've seen -6, -6.5, -6.7, -7, and -8 cc as answers. wtf? who can answer this question with complete and utter confidence? i need help determining piston to valve clearance, head gasket thickness, how much to mill the head etc etc i am running out of patience.

 

EngineKits.com has OEM replacement pistons for the Vortec 364ci which could be the LQ9 or LQ4. But it says .048" dish and given that the LQ9 is a flattop I'd assume that they're for the LQ4 and that is the same dish size as the stock pistons.

 

Well what do we know? Since 1999 the LQ4 has had 9.4:1 compression. 317 heads have always had 72cc chambers. The stock head gasket is still .052" thick compressed right? With a little math you can figure out the stock piston dish pretty close.

Just playing with an online compression calculator...
Perfect flat tops with 0 dish comes out to 10.01:1. Coincidence of an LQ9?
-5cc gets us to 9.501:1. Close but no cigar yet.
-6cc gets us to 9.405:1 Close enough?
-6.5cc gets us to 9.358:1....GM might round that up.
-6.7cc gets us to 9.340:1 Surely GM wouldn't round that up to 9.4.
-7cc gets us to 9.312:1....Again GM wouldn't round that up.
-8cc just makes the calculations even further away.

Chance are -6cc is correct, but that's just letting math guide us.


Edit: I just realized how old this thread was. Hopefully it'll help somebody down the line who searches for this info.

 

i would also like to know for the same reasons as the op.
i have seen -8cc floating around here but playing with the calculator i come up with -6cc also.