I've got a very broad question about compression ratio's. I currently have 67cc heads, with flat top pistons with valve reliefs. The car runs on 89 ocatne. I can't remember how to figure compression ratio's. But i'm going to be getting a set of sportsman II's....and i'm trying to figure out what comprssion i'm looking at by either going to 64cc's or to 72cc's....could someone please help me out. I currently have S/R torquers, and I'll be switching to Sportsman II's. I also have a superram, so i'm hoping that should be a decent setup. Thanks!!

 

Go to www.smokemup.com

Here's a direct link http://www.smokemup.com/auto_math/compression_ratio.php

AJ

 

Don't be a dummy. Port your S/R heads and reinstall them.
You'll have a lot more flow and velocity than an out of the box sportsman head. You have a good head casting, you can port these heads to flow more than you'll ever need.
260/270cfm is possible. Any Monkey can get 250+cfm out of these heads. A Sportsman head would need the same porting to equal this. Stock out of the box flow on a sportsman head is
only about 225 cfm depending on who does the preparation.
So you'll need to port the sportsman head anyways.
When you're done porting the S/R's you'll still be under 200
cc port volume with lots of flow. A big +++ for low end torque
and throttle response. That doesn't show up in hot rod magazines or a dyno test. But will show up when driving the car.
Pick up a book by David Vizard on how to port heads.
The S/R's are dealt with there.
You should be able to port and flow test (to verify flow) these
heads for far less than the cost of new Sportsmans and get way better results.

The S/R's have loads of potential onece properly ported
and you allready own them. two big +++'s