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Discussion Starter #1 (Edited)
why does my 68 390 all original motor have C6 parts...

My original motor so I was told had a S intake with c6, heads c6, and manifold c6.. the timing cover is c8.. I am confused if Ford used naythign available to build a 68.. my car was built 2 23 68.. the heads are 5L24 and 5L17... trying to figure if somehow the factory changed the motor or the original family
 

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Because the 390GT engine was invented in 1966, therefore all the parts would carry a "C6" engineering code, except for any items that were redesigned after that. How about checking the casting date codes on your parts. They should be within a few months preceding your build date.
 

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Believe the C6 cast onto the parts is a design date. The parts may have been cast in 66, 67, or even early 68 (prior to your build) but were originally designed in 66. There should be date castings on the heads and manifold.
 

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My original motor so I was told had a S intake with c6, heads c6, and manifold c6.. the timing cover is c8..
Ford part numbers are based on the year the part was designed and the vehicle family for which it was designed. The FE engine was laid out in the '50s for the big Fords, Mercurys, and Edsels. So you're going to find part numbers (and casting numbers, which are not the same thing) with B8, C0, C3, C5, C6, etc. prefixes as Ford revised parts for different applications.
 

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I'm betting the motor has been changed by someone. A 68 390 shouldn't have any "C6" castings (except maybe the block). Also, the date codes should be a lot closer to the build date. No way a Feb. 68-built car should have Nov. 65-cast parts on it.
 

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I'm betting the motor has been changed by someone. A 68 390 shouldn't have any "C6" castings (except maybe the block). Also, the date codes should be a lot closer to the build date. No way a Feb. 68-built car should have Nov. 65-cast parts on it.
Why shouldn't a 68 390 have 'C6' casting numbers? The casting number is based on the year the part was designed and the FE was a decade old by 1968. Not much of the FE changed for the Mustang application; might be wrong but I think the heads with the revised exhaust bolt pattern were the same as the '66-67 Fairlane GT/GTA?

Please explain.

On the other hand, average life for a set of valve guides in the '60s wasn't much over 50-60K miles, so it wouldn't be unusual to see the heads swapped...
 

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In 68 they would have gone to a C8 head that would have had the required bolt pattern. Scod67 mentioned the block, and probably some of the internal components would have the C6 number. You are correct in that the basic design didn't change much, but all those components were constantly being revised. Things like the intake all of a sudden needed an extra vacuum port or something like that as emission requirements changed, so they got new casting numbers as the years went on.
 

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5L24 would have been Dec 24 1965, and with that exhaust pattern used in a 1966 Fairlane, Comet or Cyclone. Those are better heads than the 68 versions.
 
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