milling heads for comp ratio increase

70Hardtop said
Hi, I am sure this has been talked about before, can anyone guide me to where on this forum if possible? I can't seem to locate the information.

The question is about how much to mill the head surfaces and inlet (intake) manifold for, say, one point extra CR. Is there a rule for LA engines that says, if you mill the heads this much, you will get this much CR increase? Also, if I mill the heads say 25 thou, is it also 25 thou off each intake surface? Or something different? My engine (273) is approx 8.5:1. I want to go to about 9.5:1. No other option is available for me at this time.

My question is, what is the rule for this? What amount taken off the heads of an LA engine (in my case, a 273) will produce approx 1.0 point increase of compression? And what is corresponding amount required to take off the intake surfaces?

Thanks!!

The surface to volume ratio when milling heads is as follows: on a small chamber 273/318 head, for every .0053 inches milled off the chamber face will reduce the volume 1 CC, for every .010 inch removed from the chamber face, it is recommended to remove .0095 from the intake face. Milling info from "How to Hot Rod Small Block Mopars" by Larry Shepard. Heads can be milled up to .060. Loose rule of thumb is, 10cc removed equals 1 point of compression.

Hope this helps