Exopar,

You can probably reach a reasonable C/R increase without milling the heads. Your current piston volume is 6.5cc and your current head gasket thickness is .046. This gives a C/R of about 8.9/1. (I'm assuming your engine is currently stock). If you would install a Fel-Pro 1011-2 head gasket which is .039 compressed thickness then your C/R would bump to 9.2/1. If you would install an aftermarket piston like the Keith Black 115,which has a piston volume of 3cc, along with the .039 head gaskets then your C/R would increase to about 9.4/1. This would be a reasonable increase without worrying about pinging. Depending on many other variables a 9.5/1 C/R is acceptable on pump gas.

I have World Windsor JR's going on my 89 which have a 58cc combustion chamber. According to World, these heads would have to be milled .070 to gain a full point in C/R. The combustion chambers of the World heads are similiar to your E7TE heads. So if your convinced to mill the heads to get the C/R bump then you would need to mill about .042 to reach a 9.5/1 C/R.

Increases in C/R should not affect the speed density system on your truck. Things that change actual volume of air passing thru the engine (better flowing heads, larger throttle body etc) and a erratic vacuum (lopey cam) will goof up the system tho. A change in C/R does not change the volume of air thru the engine. Going too high would cause pinging.

Randy