Engine Experts: Figuring Compression Ratio
Thread Starter
Le Mans Master
Joined: Mar 2002
Posts: 7,456
Likes: 2
From: Coming home from Luckenbach Texas
Engine Experts: Figuring Compression Ratio
Okay...yet another head question:
If my stock smog heads are currently 76cc, and my CR is 8.9:1 (we could say 9:1 for the sake of argument), what CR could I expect using heads with these chamber volumes:
72 cc
68 cc
64 cc
Also, what's the max CR I can get away with (using 93 octane pump gas) with aluminum heads and iron heads (non-vortec).
If my stock smog heads are currently 76cc, and my CR is 8.9:1 (we could say 9:1 for the sake of argument), what CR could I expect using heads with these chamber volumes:
72 cc
68 cc
64 cc
Also, what's the max CR I can get away with (using 93 octane pump gas) with aluminum heads and iron heads (non-vortec).
Race Director
Joined: Jan 2003
Posts: 15,172
Likes: 86
From: State of Confusion
http://www.smokemup.com/auto_math/compression_ratio.php
I'm running 10.3:1, iron Dart II heads, 292H cam, on straight SUNOCO94, but have run AMOCO93 on occasion.....
I'm running 10.3:1, iron Dart II heads, 292H cam, on straight SUNOCO94, but have run AMOCO93 on occasion.....
Melting Slicks
Joined: Jan 2004
Posts: 2,672
Likes: 1
From: New Cumberland PA
This shoud be in the ballbark:
72cc +0.35
68cc +0.8
64cc +1.2
The second part is a little tougher, it will depend on the cam and the heads. For Aluminum heads I say 10.0 to 12.0. Standard Iron heads 9.0 to 11.0. For a shorter duration cam say under 260 degrees stay on the lower end of the scale. Over 300 degrees then the upper end. Cams in between will naturally fall in the middle. I would check the cam manufacture and see what they recommend.
72cc +0.35
68cc +0.8
64cc +1.2
The second part is a little tougher, it will depend on the cam and the heads. For Aluminum heads I say 10.0 to 12.0. Standard Iron heads 9.0 to 11.0. For a shorter duration cam say under 260 degrees stay on the lower end of the scale. Over 300 degrees then the upper end. Cams in between will naturally fall in the middle. I would check the cam manufacture and see what they recommend.
