C4 Flexplate

The C4 Hipo flex plate is a C4OZ 6375 C in 1966 and C4OZ 6385 E in 1967. The C4OZ 6375 C was replaced by the C4OZ 6375 E so that all Mustang Hipo flex plates are the same. The standard 289 used a different flex plate due to the different Hipo balancing characteristics. The Hipo 4 speed flywheels were a different part number compared to a standard 289 for the same reason.

-Fred-

Jim, The reason that I use part numbers is that Ford part numbers are my second language. I was a Ford parts manager for twenty years and have been doing the Ford parts stuff for over 38 years now. I certainly know about Ford engineering numbers and have cross reference books for them. Most of what I deal with is NOS Ford parts so a Ford part number makes more sense to me. A Ford part number is also what anyone with a CD can look up to verify. I am old fashioned and still use the Ford parts books. I have more Ford parts books than most Ford dealers will ever have as I have mostly only the older versions. The older versions have part numbers that do not exist in the CD versions. Also keep in mind that some engineering numbers can be very misleading. A very good example that everyone on this forum knows is a C5AE 6015 E. There are two part numbers associated with this number but only one that matters to this forum.

-Fred-

Jim, Please understand that I am not trying to stir anything up here. The example of the bare block engineering number that I used was universal to almost every Hipo Mustang on this forum with the exception of the 64 1/2 Kars. The same engineering number is used for both a Hipo and a standard 6 bolt block. There are other parts that have no engineering numbers like valves, push rods, rocker arms, trans gears, timing chains and sprockets to name a few. I agree with you that "it's not what's on the box, but what's in the box that counts". Over these many years I have encountered many misboxed parts. Sometimes they came from Ford this way however most of the time it happened with returns from the shop mechanics or customers. With a part number I can at least look it up in the Ford book and a lot of the time be able to check the description to verify what I actually have. An example would be a push rod that you found somewhere and wanted to see if it fit your Hipo 289. If you looked it up in the Ford parts book it will give you the dimensions. That is not always the case but it works well for this example. Sometimes the Ford parts book gives an engineering number with the part number however there are usually multiple engineering numbers for many parts and the book may list only one. It is my belief that having both an engineering number and a part number is most helpful in all of our research on this forum. I do not feel that there can be too much information as long as it is correct. I certainly do not wish to make anything more complex than it already is.

-Fred-

Balancing a flex plate can be done by a qualified shop however, the total engine balance will be in jeapordy unless it is all done together. Engine balancing, when done properly, has everything weighed in grams. The only hope that you have for a correct copy of the balance on the flex plate is if you had one that was already balanced to your engine. Of course, then you would not be needing another one. If the engine was balanced as a stick shift previously, the flywheel can be used as a match to get the balance pretty close.

-Fred-