Head Milling vs. Compression

 

Ever wonder how much you need to mill off your head to make a cc difference in the combustion chamber size. What about the difference that makes in where you need to machine the port side of the intake as well as the front and rear so you get proper sealing. Now you will know.

 

Engine/Head Type

Amount to mill to reduce chamber volume by 1cc

Proper amount to mill port sides of intake for correct alignment and sealing for each .010 removed the on heads or block

Proper amount needed to mill intake ends for correct alignment and sealing for each .010 removed on the heads or block
SBC 64cc chamber .0055 .0123 .0173
SBC 76cc chamber .0059 .0123 not required
BBC 109cc closed chamber .0065 .0070 .0193
BBC 118cc open chamber .0050 .0070 .0193
Ford 65-77 289-302 engine .0060 .0100 .0143
Ford 69-77 351W engine .0055 .0100 .0143
Ford 78-up 302/5.0L/351W engines except 86 5.0 HO .0045 .0100 .0143
Ford 351C engine .0050 .0100 .0143
Ford 69-71 429-460 engine, quench head

.0050

 .0100 .0143
Ford 429-460 engine, open chamber head

.0030

 .0100 .0143
Chrysler 273-318ci engine, 57-61cc chamber .0053 .0095 .0144
Chrysler 340-360ci engine, 63-71cc chamber .0048 .0095 .0144
Chrysler B/RB engine, 66.5cc or 73.5cc chamber .0062 .0123 not required
Chrysler B/RB engine, 79/81/83cc chamber .0042 .0123 not required
Chrysler B/RB Max Wedge Engine, 81 or 86cc chamber .0050 .0120 .0170
Olds 403-455 Big Block engines .0050 .0130 .0169
Olds 350 Small Block engine .0060 .0130 .0169
Pontiac 65-67 .0061 .0061 not required
Pontiac 68-70 .0052 .0052 not required
Pontiac 71-79 .0047 .0047 not required