Is this a good compression ratio?
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Senior User
Joined: Nov 2009
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Is this a good compression ratio?
Ive got a 77 f250 highboy and i am building a 460 for it. I had the bottom half built at a machine shop because they cut me a heck of a deal. I am using the D3ve-a2a heads with the low compression and they said they put some Dished mustang pistons in it, and said they managed to bump the compression up to 9:1. Its a daily driver truck = but it will be in the mud and my foot will be in the accelerator from time to time. The heads are still factory measurements just new parts. He said that 9:1 is about as high as you want to go before you start getting into racing fuel is this true?
Laughing Gas
Joined: Aug 2007
Posts: 1,107
Likes: 32
From: Spokane, WA
You're most likely perfectly safe at 9:1...you could run crappy gas and probably get no knock. The higher the CR, the better fuel you should run to avoid detonation. Now, conversely, if your CR was lower and you wanted to keep it low, then you'd be in great shape to throw on a blower or turbo if you wanted to.
Lead Driver
Joined: Mar 2010
Posts: 5,250
Likes: 11
From: West Virginia
9:1 is good for a daily driven type performance rebuild. Some newer fuel injected cars with knock sensors and returnless fuel systems run as high as 11.5:1 on premium gas.... but tuning that close to the edge is tough on a carb'd engine unless you adjust every day. Not practical for a daily driver.
Hotshot
Joined: Mar 2007
Posts: 10,101
Likes: 40
From: Pa
I agree a 9.0:1 CR will work good for a DD. Should be able to run the crappy E10 87 sold at most of gas stations nowdays no problem. Race gas with a 9:1 CR, I don't think so. If you get some detonation on 87 run 89.
Elder User
Joined: Jan 2010
Posts: 787
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From: Hattiesburg, MS
The D3 heads are better than some other crappy open chamber heads. But, if you wanna run 87 octane, then 9:1 is probably all you want. If you run 93 octane, then you could probably bump it up a little.......but not quite as much as the 68-70 heads.
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Lead Driver
Joined: Mar 2010
Posts: 5,250
Likes: 11
From: West Virginia
its worth mentioning that it does depend on how your engine is tuned and what your timing is set to. Stock ignition with a lean tune and you can easily break stuff if you go with a high c/r.
I wouldn't run 87 in a 10.5:1 motor. just asking for trouble.
I wouldn't run 87 in a 10.5:1 motor. just asking for trouble.
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