milling edelbrock heads

[427Fastback]

Does anybody have any numbers on chamber volume change when milling..eg..for every .010 cut how many cc's does it change...(or points of CR)
I have the 76 cc 427 edelbrock heads...I am in need of more squeeze..

Thanks
Cory

[Joe-jdc]

To raise the compression one full point you would need to cut the deck .070", so for each .007 is a tenth of compression point.  However, the aluminum gets weak and will soften up easier with that much cutting.  The hardening should be taken into consideration when cutting anything over .050" according to Edelbrock/TFS/AFR, etc.  When the first aluminum heads came out in late '80s the decks were only .500", and when racers started milling them for compression, they would not hold a valve job for more than a couple of hard runs.  The decks were too thin in aluminum to remain stable.  The answer was to go to a .600-.625" firedeck, and the warpage was reduced and held the valve job much better, especially when subjected to supercharging.  Joe-JDC.

[427Fastback]

Thank-you Sir...That is what i wanted to know.I would like to raise it .7.I could skim it .050... or skim it around .035 and find a .030 (compressed)head gasket..I would prefer the .035 cut and thinner gasket..

This is just a mild 427 and i am trying to get the math back up to 10-1...I had smaller chambered iron heads on before and lost some compression going to the allum heads.

Thanks
Cory

[427Fastback]

Up date...I dug out the paper work on the heads.You know....the stuff we throw away and dont bother reading..

Edelbrock states.that for every .005 removed you decrease 1cc,and the max deck milling is .060..
With this info and the info from JDC I have all the amo I need to attain my goal and approach the milling with confidence..I have 2 different formulas to work from

I will CC the chambers after a .030 cut and see how compares to the Edelbrock figures..

Cory

[Joe-jdc]

Make sure you have the head they are talking about.  Different heads have different combustion chamber sizes, and they require different cuts to obtain the affect you are looking for.  Most Ford FE combustion chambers require .007, SBFs .0065, for each .1 cc difference.  I would do the cut in two stages if possible and check the volumn before the final cuts.  JMO, but most machine shops will check before they make the final cuts if you ask them.  Joe-JDC.

[427Fastback]

Hi..the paper work is for the FE heads and came with my heads.I understand it may be some what generic..It covers both the 72 and 76 CC heads.
I will be doing the milling at work on our CNC horizontal boring mill.I will not be milling more than .035 off the heads and will probably take .030 off and then bring them home and CC them...

I am hoping to find a headgasket in the .030-.033 range and leave the milling at .030

Thanks
Cory

[427Fastback]

No luck with a suitable .030 head gasket so i will stick with the good .040 ones......

So....opinions....If i mill off .035 I should get 9.75 to 1.If I go to .040 I will get back my 10-1..

I do understand the intake fitment and watching my pushrods..

This is a mild 427 with a 270S cam....Am I over thinking my need to go to 10-1...

Cory

[My427stang]

How far below deck are the pistons and which pistons are in it?

If the quench is tight and you arent running a big dish, it seems you should be very close to 10:1 already.

But to answer your question, I wouldn't go under 9.5, unless the bottom end was together and I had no intent to take it apart, then I'd slap the heads on and keep my mouth shut on what compression the motor had . 

Of course the other option is to sell the heads and get small chamber Edels

[afret]

You can get .030" thick gaskets from these guys.

http://www.cometic.com/custom.aspx

[427Fastback]

My pistons are Ross.They are .060 below the deck.The engine has 17,000 miles on it and there is no need to take the bottom end apart..

I am not apposed to buying the 72 CC heads.I will find a use for the 76 CC ones or build another engine around the bigger chamber..

I have been told by two engine builders to stay away from cometic head gaskets.Due to the alluminum heads and the fact that I will be leaving the heads on for years(decades) at a time..
I have friends that use Cometics on there race engines but they are frequently torn down..I have no personal experience with them..

Cory

[My427stang]

Are the pistons flat tops?  That much clearance may make it fussy on fuel if you get near 10:1

[427Fastback]

Yes...flat tops with 2 reliefs.Did not ping with the iron heads on.They measured up at 70CC.....Cory