Hello All!

I've searched on here but couldn't nail down exactly what I was wondering so thought I would ask. Currently I've got the 351m/400 in my 75 SWB mated to a C6. I understand that the bell housing and transmission case are all one unit and there are different engines that will match the bolt pattern. I'd like to keep the trans I have but have considered an engine swap for more performance in the future. What engine choices do I have with my current C6? I would prefer to go 390 but don't think that will work? Another question that is probably silly but don't know, did Ford make a 400 engine, or is the 351m/400 the only option for the 400? I've seen some online for sale and would like to clarify. Finally, is there any type of adapter available to help with the different bolt patterns? Or would that require a shorter drive shaft?

Thanks in advance!

 

Yes Ford made a 400. It was basically a 351M with a longer crankshaft stroke, and the necessary different pistons and rods. Otherwise it was a 351M - which probably only gets the "M" designation to avoid confusion between it and the 351C and the 351W...

The 351C and 351M and 400 are all 335 series engines.

The 351W is a Small Block Ford.

The 390 is of the FE series of engines.

The FEs and SBFs won't bolt to your transmission, but a 429 or 460 will... Those two are 385 series engines which share the 335 bell pattern.

 

351m400 is a decent engine, basically a factory stroked 351 Cleveland, which was a power House motor in the early 70s (Boss cougars, mustangs, Torino's, cyclones, 4 bolt mains, big valve heads, quench Chambers etc) with a bump in timing and compression you can make decent power with a 351m or 400. Dependable, too, I'm working on roughly 250 k miles on a stock 351 m. There is a 400, it' looks identical to the 351m, the only way to tell the difference without dropping the oil pan is to look at the VIN to see if it's a 351 or 400. The 351s we're more common than the 400s. I'm not sure if the C6 will bolt up to a 390 (390 is a damned good engine too) as I've been fortunate to have manual trans behind all of my Ford engines. I DO know there are different bell housings for the 351c/m400 stuff, a Cleveland uses a small block bell, and all 351/m400 uses the same bell housing as 429/460. ....so you *should* (in theory) be able to bolt a big block 429 or 460 behind that C6 without any issues.....how cool would a short bed 1975 f100 with a 429 super Cobra jet be? Damn awesome lol

 

Here's what I go by...

 

You can build your Modified block or you can step up to the 429/460. That's your choice if you keep your transmission. The 460 is probably cheaper to build except you have to buy the engine and you already have the Modified block.

The only different parts in a 351M than those in a 400 are the crankshaft and pistons. Everything else stays the same.

It's easy to say the Modified is another Cleveland but, because it has a different block with about an inch more deck height, it isn't really just another Cleveland. It for one thing is wider and heavier than a 351C. And, it has a different bellhousing bolt pattern. There may be a couple thousand Modified blocks running around that have the Cleveland bellhousing pattern, and they are worth big bucks.

There is always confusion among the newbies about the 351M/400. The REASON it's usually called that is because there is really no way to know if that engine is a 351M with a 3.50" stroke or a 400 with a 4.00" stroke, without taking it apart. So when we say 351M/400 we mean that it's one of those two engines. Yes, the M was added to the 351M because they already had the 351 Cleveland and the 351 Windsor. So with three 351s there needed to be a differentiation. The 400 which used the same block as the 351M wasn't called the 400M because there wasn't another 400 inch engine in the lineup. People, even people who should know better, call the 400 the "400M". But it's just a 400.

Here's an example...I bought this '77 F150 and the guy told me it had a 400 engine, which had been recently overhauled. But something went bad with the clutch and so I bought the clutch assembly for a 400 (12"). I bought it very cheap online and no way to return it. So when I pulled out the flywheel and set the pressure plate down and tried to line up bolt holes, it wouldn't go. I measured old clutch disk and it was only 11"! So it had the 351M clutch in it. But I knew it had a 4" crank, I'd measured. So I checked the VIJN and sure enough there was a "G" which means 351M. When they overhauled the engine it cost almost nothing extra to buy 400 pistons and a 400 crank, so they did. I had the flywheel drilled for the 12" bolt pattern and kept moving. I'm happy with the extra 50 cubic inches.

R.

 

Are you sure it's a 351M/400. These engines were offered in F-series trucks beginning in 1977.

 

Thanks for all the above responses, this is exactly what i was looking for! Very useful information. Hopefully other people will find it just as useful!

DB429SCJ- I am fairly sure that is what it is. The factory valve cover sticker says that's what it is. I suspect it was a swap at some point. I searched the VIN and it looks like it came with a 390 originally.

 

4th digit of the VIN is the engine code.

G = 302 / H = 351M (1977/79) / S = 400.