I need to increase the compression ratio on a 355 chevy engine about 0.3-0.5. How much can I have the cylinder heads (cast iron) milled without worrying about the intake face (probably a TPI intake). Can I go 0.020" or 0.025 or should I stay .015" or less.
Thanks

 

i believe .030 is considered safe, but i can't put my hands on anything right now to back that up.

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1st & 3rd

 

Thanks Ede. By worrying about the "intake face", I should have said without milling the intake manifold face to correct for angle, bolt alignment, etc.

Anyone else taken off as much as .025" w/o problems?

 

Well you can look at it this way. Most performance engines have a “decked” block. The target is to get the piston at zero and this will be about .025” off the block. This is a standard machining option that I always have done. I have not yet had intake alignment problems yet. When the block is decked or the heads are flat milled, the angle does not change. The center to center distance of the heads will decrease slightly but the angle remains constant. Using this reasoning, .025” off the heads should not cause problems.

Another method of head milling is “wedge” or “angle” milling. This method entails milling the head deck at an angle, taking more metal off the combustion chamber side of the head. By doing this, the combustion chamber CC is reduced more than the standard “flat” mill. If the heads are wedge milled, the angle is changed requiring the intake face to be milled as well.

It would be advisable to verify the amount of milling with the machinist doing the work. He will tell you how much can be safely taken off.

Mike