I have a complete 351/M and was wanting to know if these motors are worth building. Alot of guys here where I live only want a 351/W. I'm sticking with me built 302, I just wanted to know if there is a need for these motors. I've heard people at the car shows say the cost alot to build. I know any motor build will cost money don't get me wrong but these just cost more. Is this why you don't see alot of them being built like a 302 or 351/W and even the FE motors. Just curious. Thanks

 

The first thing most guys would do if they had a 351M and wanted to make some power, yet keep there accessories and such would be to get a 400 block and crank and build that.

So, you say you already have a built 302 and also have a 351M just sitting around?

Josh

 

Well, I think since a 460 swap is so easy, and the parts more plentiful, the aftermarket just never really developed for the 351M/400. There are a few places that make stroker kits and what not, just not as easy to find as a 460 or other stuff.

 

Yeah the 351/M is in a parts truck I just bought and I also have a complete 78 F250 frame with motor and trans. Have no idea whats motor or trans are in the frame. I had to take the frame to just to get the truck. I'm thinking the frame is a 4x4 frame, not sure of that b/c I didn't even go look at the frame yet. It's up at the guys other garage. I'm picking them both up this weekend.

 

The 351M is a great engine. You can pump way more torque and even hp out of a 351M than you can a 302 for the same $$. A 351M w/ 4bbl intake/carb., ceramic long tubes, no cats, smog pump/egr delete, decent plugs, 10deg BTDC timing, 110 GPM fuel pump, MSD ignition, and 93oct pump gas will put out right at 400hp and 500lb/ft of torque. If you swap the stock 351 crank for a 400 crank, and the stock 351M heads for cleveland heads you will be at around 500hp and 550lb/ft of torque. All you need to do is find a 351C and 400 core to use as parts when you rebuild the motor. You can also use the stock 351M heads and have them ground to increase the compression. If you are planning on pulling a lot, I would leave the compression low so that the motor is under less stress. I doubt you will see 500hp #s if you leave the compression under 8.5to1. If you do all the work other than the machine work, you will be around $3k for everything. A 302 with the same mods would be hard pressed to pump out 350hp and 400lb/ft of torque. Stock for stock, the 351M and 302 cost about the same to rebuild but the 351M is better for torque.

 

I had no idea that it would be that much hp out of it, and really not that much work done to it. I might need to hold on to it and the C6. Does the 351/M have any down falls as far as something I can fix and make better.

 

so let me get this straight the 351m heads and the 351 cleveland heads will both fit on the 351m?

 

The C6 is somewhat of a downfall for the 351M. It eats ALOT more hp than a C4 or manual. What you produce at the crank is not as important as what you produce at the wheels. The C6 will eat about 20% of the engines power. Personally, the C6 is the best transmission ever made and even though it eats power, it will handle a lot of stress and is a great transmission for pulling. If it were me, I would install the typical bolt ons, install a 400 crank and bump the compression up to about 8.5 to 1 and leave the C6 trans. You will be producing about 320hp at the crank and about 255hp at the wheels which is not bad considering the setup. And you will have less in it than a 302, more torque, and a better engine for pulling/hauling.

 

dentside, what would I have to do to get rid of my egr valve on my 351m that won;t hurt the motor? or the valves? thanks.

 

It is not easy to do since you will be effecting the vacuum pressure of your accessories. I removed my smog pump and EGR valve at the same time eliminating most of the vacuum lines around my engine. The vacuum advance line that originally went to the main vacuum port on the top of the intake needs to be relocated to the LH side lower vacuum port on the carb. I found this creates the best suction for the vacuum advance. In order to block of the EGR, buy a new EGR mounting gasket from a parts store and cut a piece of steel stock to about the same width/height as the EGR. Mark the studs where the EGR mounted and drill the holes in the steel plate. Then use a film of silicon on both sides of the gasket and apply the steel plate to the mounting surface for the EGR valve. Use new lock nuts to secure it to the adapter. The extra vacuum ports on your carb that are not being used, plug them off with vacuum caps and you should be good. It may be a good idea to re-check the timing and the spark advance to make sure the vacuum pressure is adequate.

 

Watch your timing curve if/when you take the egr off. I had to recurve my distributor to eliminate predetonation.

 

okay thanks for the help guys, I just wanted to know how to do this cause my truck hasn't had the smog pump on it for about 15-20 years now. Cause my grandfather took it off a long time ago. if I buy a new intake manifold that eliminates the egr valve would that be a better way to go about it.

 

Good time for a four barrel!!

 

OK, now I'm alittle more interested in this 351/M, but as far as trans it does have a C6 so thats why I was going to stick with it and my truck that I'm building is a auto also. The 74 parts truck that I bought has the 351/M and a C6. I also have to take a 78 F250 frame with the motor and trans to. The owner don't know what the motor is in the frame. Only reason he knows about the 74 is b/c it was his first truck he owned. So what is the difference in a 351/M and a 351/C. If I'm thinking right a 351/M and a 400/M looks the same (to the eye). Is there a way to tell a 351/C apart from them. I would just like to know what it is when I see it so I can make a list of what I have b/c I'm going to have to sale some of this stuff. I can't store it all. Here is why: I have one decent garage to work out of and my 79 F100 is in it right now and I'm pulling the 302 out of it b/c it is way to tired. I have a 75 with a warmed up 302 in it that I need to pull the motor and trans out of. Thats the 302 I was going to build up somemore and put in my 79. Then sale the 75. I bought the 74 with the 351/M for othe parts I need and I'm stripping the wiring out of it for my dad also, and this truck comes with the complete 78 F250 frame. So I have no room for none of the other trucks or motors. I might keep the 351/M and trans now after this. But I'm still in the same boat. So if you can tell me if and what the differences are that would be great. B/c what I don't keep will be getting sold cheap. The last thing I want to do is scrap good parts, that would be a SIN!

 

The 351m is a short stroke version of the 400. Same everything except crank, rods, maybe pistons. Same crapola low compression, same crapola cam timing. Same heads that tend to crack. The 400 came first, with the 351m intro'd in '75.

The 351c is a shorter deck block, even shorter than the 351w at 9.206 inches. The 351m and 400 are in big block territory for deck height at 10.297, which is taller than the FE and close to the 429/460.

The 221/260/289/302, 351W, 400, 351m and 351c all share the same bore spacing though, which is one reason you can swap heads around.

There is an aftermarket for the 351m/400. The usual path to power is to convert the 351m to the 400 via the 400 crank etc.

460s were a popular swap for many reasons, not the least of which is 60 more cubes.

As to the claims of 500 hp, the engines I've seen written up have aftermarket heads, cams, higher compression etc.

More info here:

https://www.ford-trucks.com/article/...00_Engine.html

Hot Rod took the long road around, but look at what they did--

How We Got Over 500hp from Ford's 400M Engine - Hot Rod Magazine