Pulled the head - wrong one!
Fleet Mechanic
Joined: Jun 2004
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From: Minnesota
Do you know what the compression ratio of the motor goes up to when .060 is shaved of the heads? Lets say the motor is all factory and all I am doing is shaving a set of 8RT or 8CM heads.
Originally Posted by 286merc
8RT heads are no better than the 8CM; true CR in a 239 comes in around 5.8. 8BA and EAC are close to each other and EAB are the best for compression.
Any flathead can easily be cut up to .060 to clean up the surface and/or raise the CR a bit. Stock 8BA volume is 76cc and the EAB is 71cc
Any flathead can easily be cut up to .060 to clean up the surface and/or raise the CR a bit. Stock 8BA volume is 76cc and the EAB is 71cc
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Senior User
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From: Lewisville, NC
Originally Posted by 286merc
8RT heads are no better than the 8CM; true CR in a 239 comes in around 5.8. 8BA and EAC are close to each other and EAB are the best for compression.
Any flathead can easily be cut up to .060 to clean up the surface and/or raise the CR a bit. Stock 8BA volume is 76cc and the EAB is 71cc
Any flathead can easily be cut up to .060 to clean up the surface and/or raise the CR a bit. Stock 8BA volume is 76cc and the EAB is 71cc
-Scott
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Joined: Jul 2001
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From: Southern New Hampshire
Originally Posted by Narwhal
What's that in psi?
-Scott
-Scott
Of course it will be less in Denver which was why Ford offered Rocky Mountain heads back in the 30's.
Do you know what the compression ratio of the motor goes up to when .060 is shaved of the heads? Lets say the motor is all factory and all I am doing is shaving a set of 8RT or 8CM heads.
Approximately 7.3
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Senior User
Joined: Oct 2003
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From: Lewisville, NC
So you're saying that my compression of about 75 psi is about what should be expected with 8CM heads? What about with 8RT or 8BA heads? Is there a resource that lists stock volumes for the different heads?
-Scott
-Scott
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Joined: Jul 2001
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From: Southern New Hampshire
.................. What about with 8RT or 8BA heads?
That was answered 2 posts ago
Is there a resource that lists stock volumes for the different heads?
Yes and no. I didnt trust the data in some books since they didnt agree with each other so I cc'ed my own
-Scott[/QUOTE]
That was answered 2 posts ago
Is there a resource that lists stock volumes for the different heads?
Yes and no. I didnt trust the data in some books since they didnt agree with each other so I cc'ed my own
-Scott[/QUOTE]
Hotshot
Joined: Oct 2004
Posts: 15,882
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From: Durham NC
Before you go milling heads, be sure to accurately measure the piston top to deck height, since you said it looks like the engine has had some machining, it'll possible/likely the deck was cut at the same time and/or higher compression pistons added.
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Senior User
Joined: Oct 2003
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From: Lewisville, NC
Originally Posted by AXracer
Before you go milling heads, be sure to accurately measure the piston top to deck height, since you said it looks like the engine has had some machining, it'll possible/likely the deck was cut at the same time and/or higher compression pistons added.
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