Compression limits
Thread Starter
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Compression limits
How high a compression ratio can you go to before you exceed the ability to use 93 octane fuel. I would like to hear about any variables that affect the answer. Thanks for your input.
I have seen 230/230 .575 lift cam and 11.75 CR on 93 octane.
I have seen 230/230 .575 lift cam and 11.75 CR on 93 octane.
Safety Car
Joined: Nov 1999
Posts: 3,891
Likes: 2
From: Houston, TX
Re: Compression limits (SpinMonster)
This really depends on a whole mess of things. I have used 12.9:1 on a daily driver, used 93 octane gas and used all the timing I thought was right(above factory!!!). This is not I have a few 12.5:1 cars out there and know of bunches of others that have been running for long periods of time with no issues.
A couple of things to look at is the efficiency of the heads, shape of the combustion chamber, size of the cam, overlap, etc.
Just my experience...
A couple of things to look at is the efficiency of the heads, shape of the combustion chamber, size of the cam, overlap, etc.
Just my experience...
Thread Starter
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Re: Compression limits (Chris@SpeedDemon)
I had no idea that some of those things came into play. Any ideas where i can read up on it?
Thanks
Thanks
Safety Car
Joined: Mar 2002
Posts: 4,928
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Cruise-In V Veteran
St. Jude Donor '09
Re: Compression limits (SpinMonster)
Here is an excellent explanation of CR and Dynamic CR http://cochise.uia.net/pkelley2/DynamicCR.html . :thumbs: :cheers:
DCR - The most important cam variable is intake valve closing point. The later the closing the lower the DCR. :cheers:
[Modified by binksZ06, 4:01 PM 5/16/2003]
DCR - The most important cam variable is intake valve closing point. The later the closing the lower the DCR. :cheers:
[Modified by binksZ06, 4:01 PM 5/16/2003]
Le Mans Master
Joined: Oct 2001
Posts: 5,577
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From: Southern Maryland Maryland
Re: Compression limits (binksZ06)
I guess I'll jump in since I am probably the guy your talking about. My old setup was 11.75:1 but I had a big cam to bleed off some of the compression. You can run that high with a big cam just make sure you always have good gas 93-94 octane. With the valve reliefs I think my new compression is around 11.45:1 but will probably act like more since my old rings weren't sealing.
Phillip :nonod:
Phillip :nonod:
Thread Starter
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Re: Compression limits (Phil97SVT)
I guess I'll jump in since I am probably the guy your talking about.
