906 88cc heads to 74 cc AL heads

[allen Wrench]

I should gain about a 1 point and a 1/2 in CR when going from 88 to 74cc right ?

 

[Chryco Psycho]

Close to that , approx 10cc = to 1 point of compression , so you should gain 1.4 all things being equal , I would recommend cometic gaskets with alum heads though , they are available in a variety of thicknesses to alter the compression to your needs

 

[Cranky]

As a general rule for open chamber heads, it's about .0042" of metal removal to gain 1cc. You need to CC your heads before starting to make sure what they are and have never been machined before....and most stock untouched heads I've checked were right at 90cc.