Howdy Back:
First a couple of questions- What cam are you running? What transmission? What is the elevation where you live? What is the average temperature where you live in July? What head gasket will you be using?
These are all factors when deciding what your CR should be.
FYI- A '79 head will have 62 cc volume chambers and is rated at 8:1. A '66 head will have 52 cc chambers and is rated at 9:1. With a stock cam, and a good distributor advance curve and initial advance it is a good idea to shoot for a CR that mirrors the octane rating of the gasoline you will most often us. ie, 87 octane - 8.7:1 CR. 91 octane - 9.1:1.
To achieve a 9:1 CR in this case, you will need to mill the head .050" to reduce the chambers from 62 to 52 ccs. The stock head gasket is a steel shim type at .025" compressed thickness. The aftermarket composite gaskets now available range from .045" to .055". YOu will also need to mill the head the difference the stock gasket thickness and the aftermarket gasket you choose. The total mill cut will be in the vicinity of .075". Stock heads have been safely milled up to .090". I personally would not mill a head past .080", but that's just me. Be sure to re-establish the oil transfer slot in the head.
Your stock cam generates fairly high cylinder pressures and high heat. An aftermarket cam with more duration bleeds of much of that cylinder pressure and allows more CR.
I hope that will get you started. Give us the answers to the ? above. Any Questions?
Adios, David
