390 to pump gas

[74390]

Looking for info on getting a 68 390 AMC motor down to a pump gas friendly C.R. (roughly 9.2 ratio). Need C.C. of 401 heads and 390 also.

[Big Bad AMX]

You'll need to drop into the eights to run 100% premium pump gas safely. My AMX is running a 9.6 compression ratio and I still run octane boost. I would run boost with a 9.2 as well.

The stock '68, 69 390 heads have 51cc chambers. The 401 heads are 58cc.

You'll find quite a bit of information in this thread including putting later dog-leg heads on an early block:
http://www.amx-perience.com/AmericanMotorsForum/showthread.php?t=98


.