Determining CR
Thread Starter
Pro
Joined: Mar 2004
Posts: 686
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From: Southeast
Determining CR
How do you go about determining your CR? Is there some type of tool or what? Is it simply a guessing matter? My motor man said that it was around 8.5-9:1, but I just put some 64cc heads on it opposed to stock and wanted to figure it out.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Typical 350 flattop has about -5cc dome volume, typical 350 dish about -11.5cc.
Typical 350 flattop has CD about 1.560" ... down in hole (aka deck height) 0.025" on uncut 9.025" block.
Typical 350 dish has CD about 1.540" ... down in hole (aka deck height)0.045" on uncut 9.025" block.
Use this handy online calculator
http://www.campbellenterprises.com/R...o%20calculator
Typical 350 flattop has CD about 1.560" ... down in hole (aka deck height) 0.025" on uncut 9.025" block.
Typical 350 dish has CD about 1.540" ... down in hole (aka deck height)0.045" on uncut 9.025" block.
Use this handy online calculator
http://www.campbellenterprises.com/R...o%20calculator
Le Mans Master
Joined: Oct 2001
Posts: 5,943
Likes: 3
From: Wildwood IL
Like mentioned above by Jackson...for accurate dynamic compression calculations, you'll need
Head cc
Piston head volume
Piston to deck height @TDC
Head gasket thickness
Bore
Stroke
Doubt you know some of these exact measurments without the motor being apart so...
In general...you can figure "about" one full point increase of compression going from 76cc heads to 64cc heads. Radical (high) duration cams also can bleed off compression due to late valve opening so that is a factor also.
HA!!! not as easy as you thought huh??? We all wish there was a tool!
Eddie
Head cc
Piston head volume
Piston to deck height @TDC
Head gasket thickness
Bore
Stroke
Doubt you know some of these exact measurments without the motor being apart so...
In general...you can figure "about" one full point increase of compression going from 76cc heads to 64cc heads. Radical (high) duration cams also can bleed off compression due to late valve opening so that is a factor also.
HA!!! not as easy as you thought huh??? We all wish there was a tool!
Eddie
Last edited by Edzred72; Feb 7, 2006 at 05:00 PM.
Le Mans Master
Joined: Mar 2004
Posts: 7,502
Likes: 1,510
From: Little Rock AR
It is quite easy to calculate if you have all the measurements. The problem is when you don't have all the measurements. 
I bought a glass burette from a school science supply store that was less than $50 to my door. That plus a little clay, feeler gauges and a piece of plexiglass is all you need to take the measurements. That, plus have the engine torn open.
EASY
-Mark.
I bought a glass burette from a school science supply store that was less than $50 to my door. That plus a little clay, feeler gauges and a piece of plexiglass is all you need to take the measurements. That, plus have the engine torn open.
EASY
-Mark.
