Thread: Head Milling

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How much can you take off a head before you start running into the intake angle issue? I've heard for every .0050 you get 1cc off. I have a set of 990 heads and looking to raise compression, it together right now. So i was thinking mill heads or just buy new pistons....

Originally Posted by Hoss Blazer

How much can you take off a head before you start running into the intake angle issue? I've heard for every .0050 you get 1cc off. I have a set of 990 heads and looking to raise compression, it together right now. So i was thinking mill heads or just buy new pistons....

What is the reason you feel you need more static compression ratio? Do you know what the ratio is now? Matter of fact, can you tell us the whole story of the motor, all the particulars?

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Originally Posted by techinspector1

What is the reason you feel you need more static compression ratio? Do you know what the ratio is now? Matter of fact, can you tell us the whole story of the motor, all the particulars?

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Looking @ a bigger cam. Right now i have the Comp Cam 11-239-3 Extreme 4x4 & I'm looking @ the Comp Cam 11-254-3 Extreme Energy. When i put the engine together years ago a lot of my buddy's still trail riding and such. Now i'm just about the only one left and do more Bogs/Runs now. Max RPM is about 5800 and looking to get higher into the RPM range, thats why i slected the Energy one. Compression is 9.7:1 or so right now. New cam likes atleast 10.5:1 or so. So if could get it to 10:1 or so maybe little bit more

Originally Posted by DennyW

On the average, if you take 0.030 off the heads, you raise compression 1/2 point. So by what you have, it would then be right at 10.2.
Also, 0.30 is ok as far as intake fit. Over that, you need to figure the angles, and remove from the manifold base to correct the intake port angles, and maintain the sealing clearances.

Thats what i was thinking, gotta call the machine shop to see how much they charge to mill....depending on price might be cheaper to buy different pistons.

old post but i add to it as i do this all the time .first off 025 is about right if the heads have not had many valve jobs. your seat angle 30/ valve angle could be about .035/050 deep on this to the deck of the head. cutting in to some of the 30 angle this is not to big of a deal but you want not to cut on the seat angle of 45.. i tru deck most all engine blocks that come to my shop many times that is 020. there . so at 025 intake will fit and can go more then 025 but bottom of intake may need to get cut i been at better the 050 off deck and heads still not much if any intake work with some intakes ... .i only cut intakes to line up ports most intake have bigger bolt hole s in the in take and have no upper tops bolt holes or ears to hook on the valve cover rail this keeping the intake from sitting down . bbc never have much piston to valve room on the intake side with very much cam . so cutting the heads down only to fined you need to fly cut the piston s is a poor deal .buy the cam put it were you want it then check piston to valve intake and ex on both heads to see what you have. the cut off the head deck if any . for any thing past 010 your looking at $60 and i go up to .050for that price thats a head with valves out of head if you want a ride or your shop is not up to my storm mill cutting head is set up for big cuts were the berco mill use a cbn cutter and is slower for this job takes many fine cuts as its at best .003 per pass and many shops use this cutter i have both mills set up both ways