c6ae-r is calld a Transition HeadOctober 5 2017 at 6:37 PM
WerbyFord (Login werbyford)
Response to Fe heads
1966 was the 1st time the FE went into a shock-tower unibody car. The taller exhaust port exit of the c4ae-g head was deemed too close, so the exhaust was lowered about 1/4" for all FE vanilla heads from then on. (The 427 and 428cj heads kept the same higher exhaust exit but Ford didn't consider the 390gt a Performance Engine apparently so it got the lower ports like the c6ae-r head.
For the c6ae-r, it is identically a c4ae-g head, except:
1. The exhaust port is the same, but the ROOF only exit is lowered 1/4" to line up with the manifolds. You can cut the lip away and the port will be the same as the c4ae-g. Otherwise the exhaust port will look "smaller". Maybe somebody cut your roof away already.
2. The c6ae-r has "Unibody Ears" since things are too tight to use the vertical bolt pattern of the big car heads. The c4ae-g does not have these ears.
Other than that I think the c6ae-r and c4ae-g are identical.
On a mild build eg 300hp or so I cant really tell the difference between stock c4ae-g vs stock later c8ae-h or d2te-aa heads. The c4ae-g would give up a little down low (and lose about 0.5 compression) but be maybe 2% better up high, overall about a wash. How much difference did you notice? Maybe the c4ae-g just had a better valve job?