Estimate on how much to mill heads?

Even though when I bought my CNC Hughes Victors they said their work included milling the heads back to the original chamber size (75 cc is what Edelbrock advertises), they looked "big" to me. So, tonight I measured the two end chambers of one head and came up w/ 82 cc for both (fractionally more for the one chamber that shows more drop-out from the CNC program).

Can anyone give me a reasonable estimate of how much should be milled to reduce the chamber volume per 1 cc? Now that I know they're actually bigger, I think I'll just take 'em down to 78 cc, same as w/ my Stage VIs, and leave the CR at 10.8.

P.S. What got me thinking I needed to measure my heads was noticing that Hughes has recently changed their CNC Victor description to say their program increases the chamber size and for additional $ they'll bring the chamber down to what ever your target volume is.

I wonder at what point they realized that 75 doesn't equal 82?

I think milling .010th is about -1.5 cc's. maybe someone else will chime in to verify it.

level the cylinder head with an accurate level (machinist). fill the chamber with fluid to the volume you want the chamber to be. take a 0-1" depth mic that's been zeroed and place it on the head with the spindle just off the edge of the chamber. slowly turn the spindle down until the fluid just jumps up onto the spindle and take your reading. that is how much you need to cut the head to get the desired volume. if the mic is too close to the fluid level to get a good read you can put a spacer of known thickness (valve bucket shim, gage block etc.) under the mic and just subtract that from your reading.

Good tip

My new indys were corrected back to 75cc brad and on the heads it said .020 was taken off to get them back to 75cc ..... also wallace has a calc for this

I think Indy's spec of milling .006" for each 1 cc is close enough, considering they have similar chamber shapes and volumes --> 4 cc = .024"

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I think Indy's spec of milling .006" for each 1 cc is close enough, considering they have similar chamber shapes and volumes --> 4 cc = .024"

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think it would need that much ? an open chamber 906 Rule of thumb is .005 for every 1 cc ????