Adam86

iTrader: (10)

So I have a few questions concerning my FI motor build. What type of compression ratio should I be aiming for on a 10 psi boosted motor with forged pistons and rods? It will be a stock cube rebuild with 241 heads and will be running on pump gas. Planning on an intercooler but no meth. I was thinking somewhere in the neighborhood of 9.5:1.
I'm using this site
http://www.csgnetwork.com/compcalc.html
to calculate what my CR should be when it's done. The only variable I'm not understanding is the piston deck clearance. Does anyone know what mine should be? Tried searching around and I can't figure out how to find it.
Thanks guys!

mattster03

iTrader: (22)

One of the easier ways to achieve 9.5:1 compression ratio would be to pick up a cheap set of 317 heads (<$200) which have a 72cc combusion chamber vs. your 241 heads which have a 66cc combusion chamber, this lowers the CR from 10.1:1 to 9.5:1 . Plus since the 317's share the same port designas the LS6 heads (243) they will flow quite a bit better than your stock 241's. Of course if you are completely rebuilding the engine there's no reason not to just put in some low compression pistons and call it good. yes 9.0:1 - 9:5:1 would be an excellent range for your goals.

mattster03

iTrader: (22)

to get that compression ratio calculator to work use 3.9 for the bore, 3.62 for stroke, 4.03 for head gasket bore diameter. 0.051 or 0.053 (seen both) for gasket thickness, 66.67cc for combustion chamber and '0' for piston done volume and '0' for piston deck clearance.

Adam86

iTrader: (10)

Thanks man! The pistons are already bought and here and I figure between replacing heads or pistons at a later date for lower compression, I would rather replace the heads. I was really considering 317s but based on my calculations, that would put me closer to 8.8:1 CR which might be a little low. I picked up a set of 241 heads for $75 and needed new heads to replace my stock 806s so I jumped on it. Didn't want to deal with those damn graphite head gaskets. I'll be using ARP heads studs so replacing the heads at a later date if needed will be pretty easy.
Thanks a lot man you answered everything I needed!