LSX_240

iTrader: (4)

I have a 2000ish 5.3l and got good deal on some 243s. I was wondering how much i should mill them to keep the compression ratio up? or possibly mill them alot to make even more compression and what might be required to do so? I dont have alot of knowledge on CC's and what has what compression ratio. I was just informed that 243s have a bigger CC and would lower my CR.
I dont plan on going turbo although i will be running spray so mroe CR would be better. Also what head gasket? THX

greenvortec97

iTrader: (1)

.030 with stock head gaskets to re gain stock 9.5:1 compression.

Nitrous likes compression also..
What used to do is run 4.8 flat top pistons in my old 5.3 with the heads miller .030 I was in the 10's for compression but dont remember how much exactly since I used stock head haskets and a tr220 cam

batboy

iTrader: (6)

You need to mill .020" to stay at the same compression ratio as the 5.3 heads.

LSX_240

iTrader: (4)

hmm mixed responses on this a friend said .030 for 10ish but you guys say .020 or .030 for stock lol any more input from some else to verify? can i run a smaller head gasket? and yes i want higher compression for more power period.

5.3 cutty

iTrader: (2)

I milled mine 40,xxx for my 5.3 with stock headgaskets ,7.4 pushrods ,ls6 cam and lifters.runs good no valve noise tuned to run 89 oct for compresson

batboy

iTrader: (6)

Listen, 243 heads are about 64cc (64.45) and 5.3 heads are about 61cc (61.15). Verify this on smokeemup.com if you don't believe me. To reduce the combustion chambers 1cc you need to mill approximately .006". Ask a machine shop to verify if you don't believe me. To go from 64cc to 61cc you need to mill "about" .020" (.006 X 3 = .018). This ain't rocket science people.

Yes you can run a thinner gasket like the Cometic, but the GM MLS gaskets seal the best.

LSX_240

iTrader: (4)

thx batboy it seems the keyword to find info on this through google was 59cc which is .030 mill according to your (and some others i talked to) calculations to get aroung 10:1 which would be great now just gotta see if a T2 cam will clear ptv and if pushrod length is fine at stock

batboy

iTrader: (6)

The reason I posted that .020" was needed to stay at the stock CR was to correct post #2.

If you want to be close to 10:1 CR, then yes, you'll probably need 59cc combustion chambers which means milling .030".