RagnZ

iTrader: (2)

i'm in the middle of a motor rebuild right now and i'm stuck on a good CR for a 347.......it's got weisco forged flat tops -3.2c, scat forged rods, stock 853 heads just got a valve job done and cleaned um up im using the stock GM MLS head gasket, stock ls1 intake, torquer 2 cam and 150 shot would like to go to a 200 shot or more if possible when i get more money.....just wondering on what a decent CR would be......i'm also not sure what the machine shop can or already has taken out of the heads and block to make them flat again but i was thinking somewhere around a 10.6 to 10.8? stock fuel system at the moment waiting for funds...has 28lbs injectors
thanks.....

massls1guy

iTrader: (9)

Have you decided on a cam yet? Once you do search on 'DCR calculator' in this room. It's a spreadsheet where you can enter the cam, head gasket thickness, head chamber volume, etc. and it gives you the dynamic compression ratio (DCR). You want the DCR to be around 8.5 to run on pump gas without detonation. By changing head gasket thickness and/or changing head chamber volume you can fine tune your static compression ratio to give you the best DCR.

To make it simple, a 'big cam' will bleed off pressure so you can run higher static compression ratio on pump gas without detonation. But a 'small cam' doesn't bleed off pressure so it won't tolerate a high static compression ratio on pump gas.