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Fe heads

October 3 2017 at 3:52 PM
Jackie  (Login 64fdgal)
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I replaced the low performance D2 heads with a set of C4AE-G heads a while back, The C4AE-G heads made a surprising performance difference, I recently Acquired a set of C6AE-R heads that look exactly like the C4- G/s would somebody please educate me on the difference, Thanks

 
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WerbyFord
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c6ae-r is calld a Transition Head

October 5 2017, 6:37 PM 

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?

 
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Bill Ballinger
(Login 65billgal)
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Prep is the big "X" in the equation, valve job, inside turn on the intake, pushrod pinch

October 6 2017, 3:07 PM 

any number of things can knock a comparison into an apple/orange comparison. The C8s are smoggers and they do well mostly by making heat. The C4s are likely to be corroded from lead exposure and they really have to be cleaned, which BTW requires some breathing protection.

 
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