Okay Guys, Here is my question. I have read/heard that Cleveland 4V heads will bolt right up to a 351M Block, even if the M was only a 2-barrel originally. I have an aluminum offenhauser dual plane intake with a Demon 4-barrel carb. I want to buy headers but why not change out the heads so I don't have to have adapters for them? Will it work? Thanks for all replies!

 

yes the heads will bolt on no problem. the 351C, M and 400 are all the same family, just that the 351M and 400 are taller deck heights then the 351C is.

the only thing is that the intake has to be for a 351M or 400 engine and not a 351C engine. the 351C intake is too narrow. if you have an intake for the 351M/400 engine the other problem is going to be that the intake ports on the 4V heads are huge compared to the 2v heads and you will have a huge mis match and the intake might not cover the port properly.

just a word of advise. just putting 4v heads on a stock 351m is not going to really improve anything. the 351M in stock form has real low compression, retarded timing chain and a lousy camshaft that will not take advantage of the 4v heads. the 4v heads have huge ports and valves and really needs a higher compression ratio and high rpm capable motor to take advantage of them. if it was me, i would rebuild it into a 400 (easy to do, just swap crank and pistons) shoot for around 9.5:1 compression, decent cam, good timing chain, recurved dist and find either some Australian heads ( they have the small chambers with ports and valves sized between the 2v and 4v heads) or opt for the CHI 3V heads that make incredible power.

but then it is your engine and money so whatever you do is okay.

rgds
Mike

 

To use the 351C heads on a 351M/400 you will need a spacer between the intakemanifols and the heads.
Now to make it run correctly - cam - dizzy - timing gears/chain and High compression pistons.

 

The size of the ports, both intake and exhaust, is what determines the designation of 2V head or 4V head. It doesn't mean you can't use a 4V carb on 2V heads. The ports on the 4V Cleveland heads are so large, they don't start making efficient power until around 4000 rpms and up. Not too many people drive their trucks in the 4-7000rpm range, or want to. You would be far better off to retain the original heads, and use an aftermarket 4V intake to match the smaller ports, and the correct headers, too. It will keep your power band in the area you'll be driving the truck in.

You didn't say which Offy intake you have or what it fits, or the size of your Demon carb, but that is another area you want to be careful of. To get the most out of any engine, but particularly the 351M/400, it's critical your parts match. It's easy to go overkill, especially with carburetion.

 

Wow, What an abundance of valuable information gang! Thank you all. I bought the Offy intake at a swap meet years ago but my understanding was that it was indeed for a 351M and it did bolt right up with a new valley pan in place. It is a dual-plane and I understand that that is a good thing.The 4-barrel carb I bought was a 525 or 550 Demon rebuilt from Jegs. I've only fired it up once and it seemed to run okay. I didn't run it for long though because I did want to get the engine too hot, I had the fan off at the time. Thanks Wayne, Dick, and Mike for your input. Additional info is more than welcomed here! Jay

 

Dual plane is indeed the right way to go for the street. I'm no fan of Demon carbs, but your luck may vary.

 

Okay Albuq F-1:
I'll bite, tell me more about why you don't like Demon carbs, just the curious type.JNB

 

My 2 cents: just buy a Cloyes double roller timing set, and set to "straight-up". Keep everything else you already have.

EDIT: my two cents won't buy much.

 

Jay, it sounds to me like you have an ideal set-up. Offenhauser makes great intakes, and your carb isn't oversized. You should be very happy with what you have. You will lose far more than you'd ever gain by changing to 4V heads for performance, drivability, economy, everything. Save the monster ports for the Mustang restorers who think they have to have them. ;-) If you feel the need to run headers, that's fine. Just order them for your current application.

 

Actually, 351Ms were issued with 351 Cleveland heads!

 

They aren't fundamentally different/better than a Holley, same operating principles, so what's the advantage? They cost more, parts are scarce locally, gas mileage is just as poor. The Edelbrock Performer carbs (Carter design) are much better IMO, with the metering rods. The new Demon two-barrel is getting better reviews, maybe they've improved.

 

Julie, in what applications were the "cleveland" as in C heads issued on the 351m/400. I had not heard that before, but maybe missed something.

BTW I have a 400 in my 78 Bronco that has an edlebrock intake and 600 4barrel and it seems to be a pretty decent combo. The heads on that engine came off of an early 70's 400 out of a car. I'd have to check again for the date code on the heads. The engine has plenty of low end torque and I use the beater Bronco for mostly off road playing.

 

It's probably not entirely accurate to say the same heads were used on the earlier 351 Cleveland, and the later 351M/400's. Valve, port and combustion chamber shapes and sizes were revised somewhat over the course of the production run from 1970 to 1983. One could say they were fundamentally similar, though. They will interchange, as part of the same engine family.

 

Just quoting the source - could be wrong. Check out this Specs page - scroll down to the 335 series engine specs:

Ford Classics - Engine Specs

The 351M was introduced in Model year 1975 and replaced the 351 Cleveland whos last year was 1974.

Quote:

"When the 351 Cleveland was withdrawn after the end of the 1974 model year, Ford needed another engine in the 351 cubic inch (5.8 L) class, since production of the 351 Windsor was not sufficient and the 390 FE was being retired as well. To replace the 390, Ford took the 400 engine's tall-deck block and de-stroked it with the shorter throw crankshaft from the 351 Windsor, and taller pistons, to produce a 351 cubic inch (5.8 L) engine whose components were largely compatible with the 400. This engine was called the 351M and as a back-formation the taller-deck block became known as the M-block.

The M designation is commonly referred to “Modified”, and is derived from the use of both "Cleveland" (block, heads) and "Windsor" (crankshaft) components in the same engine. A "Modification" for the parts intended application so to speak.

Another origin of the M designation may have come from where the engine blocks were cast. It follows the naming convention set forth by the 351C (Cleveland) cast at the Cleveland Foundry and 351W (Windsor) where the majority of the blocks were cast at the Windsor Casting Plant. From the introduction in the Model Year 1975, the 351M engine blocks (which are the same as the 400 engine block) were all produced at the Michigan Casting Center (MCC) in Flat Rock, MI or at the Cleveland Foundry (CF) also known as the Cleveland Casting Plant (CCP). To help distinguish it from the other two different 351s, the logical choice was to use the Michigan Casting Center, hence the “M” designation for 351 Michigan.

The 351 Cleveland had a well known, good reputation in the public. For a couple of years after the introduction of the 351M, Ford marketing called the engine the "351 Cleveland". This led to confusion as to what 351 version was actually in the vehicle.

Later, car enthusiasts incorrectly referred to this engine as a "351 Midland" presumably a reference to Midland, Michigan a city just northwest of Saginaw or reference to an iron foundry in Midland, Texas. But the Ford Motor Company never owned a “Midland” factory."

End quote

 

welp learn something everyday . didna realize the 351 m used cleveland heads . ran a 400 with 4bbl heads in a sportsman dirt car , a maverick , and i got the required intake spacers from rousch , and i think they still have them . the ignition system from one of my 429's was used in it . i think i got the pistons from rousch too ...... too long ago don't really 'member ................