Hey guys,

Up til today, I always thought I had a 351m in my 78 F250 SuperCab... However, I got my LMC catalog (probably won't buy much, if anything, mainly used for part reference), and decoded my VIN. According to this, my engine is a 400. I looked at the sticker on the valve cover again and indeed under Engine Displacement it says 6.6 L (400 CID). Are there any other differences I should look for to distinguish between if the engine is a 351 or a 400? I'm thinking it is a 400, due to the VIN, and what it says on the engine sticker. Apparently the P.O. didn't catch this either, because he was advertising it as a 351.

Also... In LMC I was looking at the different transmission types and how to identify them. I looked at my tranny pan and it's the L shaped one, which according to LMC is a FMX (cruiseomatic) transmission. Is this just a variation of the C6 with cruise, or is it a whole different tranny? Thanks guys.

 

Engines look the same on the out side. I'v had both and liked the 400 best .

 

FMX was made by borg warner for ford. Steel case never had good luck with them. C6 had an aluminum case. Heavier duty than the fmx. Just my opinion.

 

FMX is cast iron case with a removeable bell housing. C6 is an aluminum case with an integral bell housing.
351M's and 400 are identical on the outside, the only difference is the stroke.
Here are a couple of pictures of an FMX tranny.

 

But I mean since the VIN and sticker on the engine say it's a 400, is it most likely a 400 then?

EDIT: Thanks for the pics mike... Anything in particular that you know of that goes wrong with these FMX tranny's? It shifts real good right now.

 

I'd say it's a 400. Like they say about the great 360/390 debate, the only way to know for sure is check the stroke.
As for the FMX. It's old school engineering going back to the old Ford-O-Matic days. If it is an FMX in your truck, someone swapped it. Originally, the only trucks that came from the factory with an FMX were F350's with the 300 cu in 6 cylinder.
They can be made to perform (The '64 427 Thunderbolt Fairlanes that had automatics came with the Lincoln version of the FMX's ancestor) but parts can sometimes be difficult to find.
I don't know of any particular issues with the FMX.

 

D'oh! It is a C6 lol. When I was looking at the tranny pan diagram in the magazine it says FMX right above the L shaped tranny pan. So its a C6 then, which sounds like a good thing based on what you.guys are saying

 

Yeah, In my opinion the C6 is the best auto tranny that Ford ever built.