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? Thanks
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Optional read : Background info: I want to increase CR a little on my freshened 1967 273. It is a budget rebuild and bottom end is all done (so I can't get the block decked).
Cam being used is a small solid grind I had lying around and the 1967 was the last year of the mechanical cams anyway. (this had been converted to hydraulic many years ago). So with a lively cam I would like a CR of around 9.5:1. Factory was only around 8.5:1 and since I have to use 318 head gaskets, the CR will be even lower.
"Budget" means I have reused the original pistons which were all in amazing condition and got a hone and new cast rings (bores were very good, virtually no lip and taper within acceptable tolerances). Budget also means I want to keep the original valves, although I still have the option of buying stainless valves (flat head valves will give higher compression over the factory dished ones) but this means a lot more expense plus the cutting of the seats again. All valves were great and seats came up well with a good hand lap. The four worn valve guides were redone and those seats re-cut again.
Cheap as it was, the bottom end still got treated to ARP bolts with resized rods and new oil pump and SA Gear DRTC with steel (not cast) gears. Forged crank remained at 0/0
So the only option to keep costs down is to mill the heads down.
My question is, what is the rule for this? What amount taken off the heads will produce approx 1.0 point of compression? And what is corresponding amount required to take off the intake surfaces?
Thanks!!
