How much static compression can I run with XR276HR ?
Thread Starter
Racer
Joined: May 2004
Posts: 288
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From: Tigard OR
How much static compression can I run with XR276HR ?
How much static compression can I run on a 383, with aluminum heads, .041 quench with flat top pistons, with a Comp Cams XR276HR cam (224/230) and avoid detonation with pump gas ?
I know that the the cam intake duration establishes the intake closing point, but I don't know how to calculate the desired static compression based on the camshaft intake duration?
I know that the the cam intake duration establishes the intake closing point, but I don't know how to calculate the desired static compression based on the camshaft intake duration?
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
Better than just giving you an answer, here's a good primer on theoretical Dynamic Compression Ratio which should help, and it includes a handy DCR calculator you can download...
http://www.empirenet.com/pkelley2/DynamicCR.html
Note that I refer to it as "theoretical" DCR, as actual DCR's = CR x VE% at a given RPM, which isn't so easily calculated, but IMCO it's still a good reference. That said, with that cam I'd shoot for ~8.0 - 8.25:1 DCR, since it's a good idea to leave some margin when VE's start getting up there (assuming good heads).
http://www.empirenet.com/pkelley2/DynamicCR.html
Note that I refer to it as "theoretical" DCR, as actual DCR's = CR x VE% at a given RPM, which isn't so easily calculated, but IMCO it's still a good reference. That said, with that cam I'd shoot for ~8.0 - 8.25:1 DCR, since it's a good idea to leave some margin when VE's start getting up there (assuming good heads).
Last edited by TheSkunkWorks; Apr 30, 2010 at 09:23 PM.
Melting Slicks
Joined: Apr 1999
Posts: 2,010
Likes: 3
From: Moon Twp. PA USA
How much static compression can I run on a 383, with aluminum heads, .041 quench with flat top pistons, with a Comp Cams XR276HR cam (224/230) and avoid detonation with pump gas ?
I know that the the cam intake duration establishes the intake closing point, but I don't know how to calculate the desired static compression based on the camshaft intake duration?
I know that the the cam intake duration establishes the intake closing point, but I don't know how to calculate the desired static compression based on the camshaft intake duration?
I don't believe static CR is based upon cam intake closing, this is for calculating dynamic CR.
Go to one of the sites where you can imput your specs and get the STATIC CR.
FWIW, I run a 383 with a CC XE274H cam, TF aluminum heads, static CR is 10.3, dynamic CR is a calculated 8.2. Runs fine on 89 octane. Never tried (or will I ever try) 87 octane.
Thread Starter
Racer
Joined: May 2004
Posts: 288
Likes: 0
From: Tigard OR
Better than just giving you an answer, here's a good primer on theoretical Dynamic Compression Ratio which should help, and it includes a handy DCR calculator you can download...
http://www.empirenet.com/pkelley2/DynamicCR.html
Note that I refer to it as "theoretical" DCR, as actual DCR's = CR x VE% at a given RPM, which isn't so easily calculated, but IMCO it's still a good reference. That said, with that cam I'd shoot for ~8.0 - 8.25:1 DCR, since it's a good idea to leave some margin when VE's start getting up there (assuming good heads).
http://www.empirenet.com/pkelley2/DynamicCR.html
Note that I refer to it as "theoretical" DCR, as actual DCR's = CR x VE% at a given RPM, which isn't so easily calculated, but IMCO it's still a good reference. That said, with that cam I'd shoot for ~8.0 - 8.25:1 DCR, since it's a good idea to leave some margin when VE's start getting up there (assuming good heads).
Race Director
Joined: Apr 2000
Posts: 17,665
Likes: 194
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Seriously that's where you want to be you can run 91 octane at that DCR level. Be careful at first, start with the best gas and low timing then crank the timing up if no pinging you can try 91, mine runs on 91 no problems with a bit higher compression bit because of the cam the DCR is about the same
Melting Slicks
Joined: Jul 2006
Posts: 2,274
Likes: 481
From: Salmon Arm, BC
I run that same cam in my 406. My mathematical compression ratio worked out to 9.92/1, and on premium pump gas I have no issues whatsoever. I can't remember the dynamic CR but I'll look for it and report back.
Thread Starter
Racer
Joined: May 2004
Posts: 288
Likes: 0
From: Tigard OR
Wow I was way off
Seriously that's where you want to be you can run 91 octane at that DCR level. Be careful at first, start with the best gas and low timing then crank the timing up if no pinging you can try 91, mine runs on 91 no problems with a bit higher compression bit because of the cam the DCR is about the same
Seriously that's where you want to be you can run 91 octane at that DCR level. Be careful at first, start with the best gas and low timing then crank the timing up if no pinging you can try 91, mine runs on 91 no problems with a bit higher compression bit because of the cam the DCR is about the same
OK, seriously, thanks for the advise...
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