i just cc'd my gt40 heads out at 69 cc's i do beleave that the origonal d0oe heads were about 60cc's federal mogul the kit i got has sealed power pistons that are supposed to yield a 9.17:1 comp ratio with 63cc heads which is about what im aiming for (~9.25:1) if i am correct i need to mill these heads down to about 64cc's to get this, but im not so sure how much milling will remove how much. which is all i really need to know for now because i will assemble the short block, and then measure deck height in order to more accuratly calculate the ratio. if anybody can help i will appretiate it!

 

the machine shop should know and handle all of that. are you sure about that CC size on the gt40's. that seams hi to me

 

It's possible after cutting and grinding the valve seats. The valves sit into the head a little farther. If you do get your heads milled you should bring your intake in and have it done to match.

 

I am also surprised the GT's are 69, I would expect 63-65 cc's. A .030 cut off the heads equals approx .5 increase in comp ratio & .060 off is about a full point increase in comp ratio. Remember that over a .030 cut and you could run into intake manifold bolt mis-alignment & may have to machine the manifold sides accordingly. Bill.

 

i would have the machine shop measure those heads to make sure that CC is correct before milling anything. would sure suck if it was not correct to begin with. best to be sure vs tossing those in the garbage

 

Iron Gt40's are normally 64 cc in stock form. I have the same heads.