Cylinder Head Milling
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Melting Slicks
Joined: Sep 2004
Posts: 2,412
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Cylinder Head Milling
I had a cyl head shop guy tell me today that I wouldn't be able to mill my 75cc heads enough to effectively raise the compression 1.5 points. Is this true? They are aluminum angle plug heads from AFR, sbc.
I could swear that my neighbor said that he had his heads taken down to 68ccs, same heads.
I could swear that my neighbor said that he had his heads taken down to 68ccs, same heads.
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Joined: Sep 2006
Posts: 78
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From: Nashville NC
I had a cyl head shop guy tell me today that I wouldn't be able to mill my 75cc heads enough to effectively raise the compression 1.5 points. Is this true? They are aluminum angle plug heads from AFR, sbc.
I could swear that my neighbor said that he had his heads taken down to 68ccs, same heads.
I could swear that my neighbor said that he had his heads taken down to 68ccs, same heads.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
I had a cyl head shop guy tell me today that I wouldn't be able to mill my 75cc heads enough to effectively raise the compression 1.5 points. Is this true? They are aluminum angle plug heads from AFR, sbc.
I could swear that my neighbor said that he had his heads taken down to 68ccs, same heads.
I could swear that my neighbor said that he had his heads taken down to 68ccs, same heads.
~.006 mill = 1 cc
~15cc = 1.5 pt increase in CR
.090 mill for 1.5 - not going to happen unless the deck is VERY thick. Contact AFR to get their take on that much of a deck. You're also in a zone where the valves are likely to have significant bore shrouding...which is why heads get angle milled.
Again, you'll need to cut your manifold big-time as well as the front/back cam valley gasket surface.
Still a bad idea IMHO, but it's your engine. All this for a 4.5% or less increase in power...
Last edited by billla; Oct 13, 2007 at 01:23 PM.
Melting Slicks
Joined: Jul 2005
Posts: 2,060
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From: winter haven florida
St. Jude Donor '12
i had afr take my 75's down to 72cc to get me at 10.5 to 1 comp. and had no problems at all but i dont think i would have gone much more than that. i would call them. what is your current set up and why are you shooting for the 1.5 bump?
Race Director
Joined: Apr 2000
Posts: 17,676
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
From my experience with Edelbrock ( Vic Jrs ) the 64cc heads are not just milled down 7xcc heads. You also have to change the intake manifold angle and unless you have the exact factory measurements and know how, it can be quite hard to get the correct geometry.
In your case the 75cc heads might even be a different casting than the 64cc head, milling that much seems to be a little too much
My Vic Jrs were milled to 64cc from there 70cc version ( they didn't actually have a 64cc version at the time ) and the machinist didn't have the know how to change the intake angle and I had to get my intake machined which was a pain in the azz too
In your case the 75cc heads might even be a different casting than the 64cc head, milling that much seems to be a little too much
My Vic Jrs were milled to 64cc from there 70cc version ( they didn't actually have a 64cc version at the time ) and the machinist didn't have the know how to change the intake angle and I had to get my intake machined which was a pain in the azz too
Last edited by MotorHead; Oct 14, 2007 at 01:35 PM.
