I just bought a '77 f150 4x4. I was told that it has a 351m- code says it came with a 400m. Original owner said that he rebuilt original motor- recent owner (that I bought it from) is a young mechanic and thinks it's a 351m. I've previously owned a 351m- and had always considered it a failure compared to other motors- But I am open for all info and, having learned it's a cousin to the cleveland helps. It runs good at idle and throttle- good oil pressure- but seems rather timid. It has a edelbrock intake and 4b carb (600?). Gets 13-15mpg hwy.

I haven't played with timing or tuned it yet. I have the following questions:

1. How can I determine whether it's a 351 or 400?
2. Other than basic timing- what simple things can i do to improve performance?
3. Can the modified be built to be comparable with a windsor or stock 360 fe?
4. Since I want to go propane as a dual fuel- anyone do that with an M?
4. Have i taken my antipsychotic meds yet? (obviously not)

thanks and love the site.

 

Roger,

1. As far as I know, the only way to definitively tell the two apart is by the crank. A 400 wil have a 5 or M5A cast into the first counterweight behind the timing gear. 351s have a 1 on theirs.
2.Exhaust is a big problem for these engines. Performance can be dramatically improved by opening up the exhaust and allowing the engine to breathe.
3. Sure -I don't think there's much difference anyway in stock form. Guys don't flame me for this, it's a generalization.
4. I have no intelligent input here, check out the alternative fuels forum.
5. Unfortunately, there are no medications for the sickness we all have.

All the Best,
Ernie

 

If you're keeping the stock cam you can get an aftermarket, or (maybe) pre '72 timing set which will advance the cam and help low end.

 

The 351M has a 3.5" stroke, while the 400 has a 4" stroke. You can measure the stroke by removing #1 spark plug. Rotate the motor to TDC. With the battery diconnected insert a wire or long screwdriver into the spark plug hole, mark the wire where it exits the plug hole. Manually rotate the crank 180 degrees to BDC. Again mark the wire. Remove the wire and measure the distance between the marks. They should be 3.5" or 4.0".

To improve performance you can go to dual roller timing chain with 'straight up' timing instead of the 4 degree retarded stock timing chain.

You need headers also.

In addition increased compresion and a decent cam will help a lot.

 

The only differance is in the crank. I have a 78 bronco that came with a 351M. The kid I got it from was looking for quick hourse power. He put on a cheap aluminum intake and a holly 650 4bbl. It DID NOT work. I built a 351M into a 400 with a nice low cam, an edelbrock intake, with an edelbrock 600 4bbl. Headers help, but can cook starters. I also had it line board, witch helps oil pressure. And board out .060 . After I was done it came out to be 402cid. It cost about $4,000-$5,000 with everything I did. But the power that truck has is incredable.

 

Tas- how was mileage affected?

Great input and I will measure depth on plug#1- would not have ventured there myself- Thanks-i'd really be surprised if this is a 400. I don't understand why I am getting good mileage out of it. 3.5 gears help some as do the 2358516 tires pumped to 50lbs. Can't wait to tinker with it a bit and see if i can screw it all up.

I have to admit that I'm an optimist regarding power and economy. I think I can get both with the right setup- just don't know what that is outside of an FE or W engine. Or, more precisely, within a M. I will pursue dual fuel with propane- so I know I will need to build an engine with the right heads and 10-1 to 11-1 compression to balance between the two fuels. I am after low end performance as in torque and economy which tie in ok- I'm wondering if the stroke of the 400 would be adequate or if i should go with an fe or W.

There ya have it-

 

AS far as milage goes, the old engine got about 8-10 mpg. With the new engine I got about 12-14 mpg. Now add in the fact it's got 4:11 gears with 6" of lift and 36" tires. In my opinion, I would stay with a 351M or build a 400M. I don't know where you are, but I may be able to help you out with some parts. If your interested?

 

Tasdevil-
I would say youve got me sold - I would enjoy joining the ranks of those performing well with the 351-400- just cause not many do it right. I will have to ck and see what I have first ie 351-400. I live in western (missoula) Montana- my motor already has the eldelbrock intake and 600 carb so I'm a step ahead there- I will need to plan on a setup that will give me 10.5-1 compression for the dual fuel. What do you have for a cam? I've heard good things about 270-290 with.5" lift. I would like to get more details on what you have in yours so as to not reinvent a failure. Getting that kind of mileage out of your truck is absolutely incredible- unheard of out of this block- So I am very interested. WHere about are you Will Copy this for pm.

 

roger
I've never been much of a salesman, but I know you will like the power. On the cam, it sounds like your on the right track. I looked up the spec on my cam, crane part # 523971 , intake- 2667 , exhaust- 2847 , lift: intake - 461 , exhaust - 493 . With a set of crane lifters. The intake is an edelbrock, performer 400. With an edelbrock 600 4bbl. I used headman headers and a very custom dual exhaust, luckily I had access to a pipe bender. But I also cooked 3 starters, and had to build a heat shield out of stainless steel, and reroute may trany cooler lines away from the heat. In hine sight, I should have gone with fender-well headers. By the way, I live in central connecticut. I don't know how the dual fuel thing will effect things. My suggestion would be to build an engine first, then do the weekend swap.You will tie up the truck less, the machine work alone took a month, before I got block and heads back. If there is anything else let me know.

 

Whoa....

If you want any driveability you're going to want a Comp 255 or 265 DEH cam.

 

That Crane Cam #523971 has an advertised duration of 248I/260E. The intake center line is about 113 degrees, which is a 3 degree retard built-in. With a flattop piston and open chamber heads, the 57 degree IVC will produce a DCR of 7.6:1. This is OK with most gasolines. The overlap is only 34 degrees. It is listed as a fuel economy cam. The torque at 2000 RPM is 459 ft-lbs.

The 255DEH has an intake center line of 106 degrees and is advanced 4 degrees. With the same motor the 53.5 degree IVC will produce a DCR of 7.8:1. This should run well on midgrade. The overlap is 40 degrees. The torque is 458@2000 RPM.

If you plan on going to dual fuel and raise the CR to 10.5:1 with Aussie heads and Tim Meyer's flattop pistons with a 21cc dish, the 255DEH will raise you DCR to 9.0:1. This is too high for pump gasoline, although it may be OK for Propane. The Crane cam will give you a DCR of 8.85:1. Again too high for pump fuel, even with quench.

A Comp Cams 275 DEH has an IVC of 63.5 degrees ABDC. The DCR of the motor with Aussie heads and 10.5:1 CR is 8.5:1. This is the absolute maximum for 93 Octane fuel even with quench. This cam has 60 degrees overlap. I would run this cam 4 degrees retarded to produce an IVC of 67.5 degrees ABDC. The DCR becomes 8.2:1 and should run easily on 93 Octane fuel. The torque at 2000 RPM is 422 ft-lbs and the peak torque is 445 ft-lbs@4000 RPM. The Peak Horsepower is 393 @5000 RPM.

All these figure are based on gasoline, I have no information on propane. I would expect lower numbers.

 

Ok matts72- Testify! (I want to hear what ya got to say- I want a motor that is low range torque happy and decent mid range. I need decent mileage and folks are getting it out of a 400 if built right- What would you suggest? I have a edelbrock performer intake- 600 4b carb of same make. What would you combo up ifn you were wanting what I do?

Thanks much.

thanks to you to danlee- I sent you a pm

 

also taz- thanks again. getting good stuff here but also learning how ignorant I am and I need to read up a bit. Will be doing that soon.

 

Roger;

To digress a moment, I understand the substantial difference between the 351m and the 400 are the pistons, with the height above the wrist pins making up the 1/2" difference in piston travel. If that is true, then both engines could use the same connecting rods and crankshaft which is what I have read in the past. I obtained a lot of supporting information on this and other topics from this forum.

I run a stock 351m in a 1980 short box 2wd, with a C6 tranny and a 2.73 rear end. I have alternated between a Holley 2 bbl carb with 500 CFM, and a couple Motorcraft 2150 2 bbl carbs, one with a 1.03" venturi, the other with a 1.23" venturi.

The best overall fuel economy was with the Holley, followed closely by the larger CFM Motorcraft. I averaged 10 miles per Imperial gallon with the smaller Motorcraft, and a much healthier 14 mpg with the Holley.

I have received mostly negative comments from friends who have experience with this "smog" engine. That said, mine runs like a top and delivers strong acceleration and performance throughout its RPM range, which isn't a whole of range compared to any modified engine.

I got a noticeable improvement in performance after installing the recommended AC#26 plugs gapped to the .045 spec.

Keeping my fuel clean proved to be the most difficult problem thus far. My vehicle sat in a farmer's field for 7 years without any cover, without being turned over, and sitting on its fully inflated tires. I was prepared for major body metal corrosion, disintegrated soft interior components, rusted out brake lines and every other thing associated with abuse and neglect.

Believe it or not, I have driven 70,000 kilometers on those same tires with no sign of being worn out yet; there is no signifigant body rust, other than a few minor surface blemishes. The interior was like new, and every bulb, accessory or component worked then and continues to work today.

I wish I had the same to say about fuel delivery. I am embarrassed when I think about the aggravation and hassle I put up with before I replaced the fuel tank. I have only myself to blame, and replaced every piece of the fuel system except the tank, and some items more than once. I wore out two mechanical and one electric fuel pumps, replaced the 5/16" fuel line, and a few months later upgraded to a 3/8" steel line. I replaced fuel filters every second week or two, including one in-line before the pump, a second inline after the pump, and a third inline threaded into the carb.

I figure I filtered enough small sand-like particles to fill an average seaside beach ! Other than gaining a lot of experience twisting wrenches, little was gained by delaying the replacement of the fuel tank.

I was once told that one of the inherent weaknesses of the 351m and 400 was a block that had comparatively thin walled cylinders, and one was urged to use caution when considering boring them out. That had me worried a little bit about the overall durability of the engine.

I blew that away one sunny afternoon en route to a job site at Whistler BC, about 100 miles or so from home. Named the "Sea to Sky Highway", this cliff hugging 35 mile segment of twists and turns, can be one of the most exciting pieces of road to drive in good conditions, and a death drive when conditions are not good.

I had changed my oil and filter the night before, and did the rountine checks and adjustments. I had been patiently awaiting the upcoming passing lane having been caught behind an 18 wheel tanker full of fuel. I passed him at about 120 klicks and was checking my rear view mirror that I had cleared him when a saw a burst of blue smoke. Looking at my gauges, my oil pressure reported zero PSI, and it sounded like I had a blender full of ball bearings under the hood.

The choices were ugly; how do you pull over on a roadway that has virtually zero shoulder, and with the letters PETERBUILT filling the surface full area of my rear view mirror ? There was maybe two or three truck lengths between me and the tanker I had just passed, and we were both doing around 60 - 65 mph. Believe it or not, I carried on that way for at least another mile before I could safely pull over.

When stopped I couldn't fathom the racket of metal smashing against metal. I hestitated shutting her down fearing the coolant temperature would go ballistic, and what remained of the engine would melt down into a slag-like turd of molten metal that cooked its way through the earth's upper crust.

A few hours later, the compassionate tow truck driver delivered me and my fallen truck to the nearest auto repair depot, where I intended to assess the damage. There was not a hint of liquid anywhere to be found under the hood. I could have used the dipstick as a shaving mirror as its surface looked more like a piece of ceramic tile that was glazed in a pottery kiln.

I had pinched the oil filter seal the night before, and 8 liters of lubricant had been deposited on the road surface between here and home. The puff of blue smoke I saw was the last drop of fossil material to be found within that engine as it atomized into the atmosphere. The needle on the oil pressure gauge had been sucked against the its stop pin with such force that it had bent into a permanent semi-circle !

I added 8 fresh liters of 20-50 multi-grade along with another filter and fired her up. I was pleased the noise seemed to be coming from the top end rather than bearings and conrods and the like. It was now about 10 PM, and the rain had turned to snow, and I decided to continue my trip as Whistler was only 30 miles or so down the highway.

I was amazed when I opened the hood on my arrival in Whister. That engine had settled right down and ran smoother and quieter than at any time in the past. Could I have lucked out ? and by some miracle, been spared the hassle and expense of replacing the engine ? It would be a first in my life experience were it so.

That took place late last October, and I have driven about 10,000 miles since that incident. A couple of weeks following an oil change, the word "SAFE" can still be clearly read on the dipstick through the honey coloured oil.

It appears that I not only cooked 8 liters of oil out of the engine that afternnon, but as well, all the sludge and toxic substances that had accumulated over its twenty five year lifespan had been set free as well. The only thing exaggerated in the preceeding story is my choice of words. The Chief Clerk of the Highway was smiling at me that afternoon, don't you think ?

I visited this site today to review any posts that dealt with installing a new timing chain. For the first time I hope to complete some preventive maintenance instead of incurring the additional cost and inconvenience of having to be towed home at an awkward moment.

I have no reason to suspect the life expectancy of this inferior smog engine will be any less as a result of its many brushes with death. I guess an engine could have a soul after all, and what the heck, maybe I should treat her with a little more kindness and affection given what I've put it through. All reports seem to indicate a positive response to the fresh approach and attitude on my part.

I'd say build yourself a quality 351m, and don't let the nay-sayers deter you from the objective. From all accounts I have read, the result can be an awesome screamer for minimal cost. I wish I had the bucks to re-build mine right, but I'll have to be patient for quite a while longer.

Whatever your decision, good luck with it, and remember to keep that vehicle between the ditches whenever you can !

JT

oops, I just realized this is no quick reply........ sorry all !

 

MVtofino,

I agree with much of what you say, but you have some mis-information. The 351M and 400 use the same connecting rod, but the 400 crankshaft has a 4.0" throw vs the 361M crank has a 3.5" throw. This gives the 351M a shorter stroke, and it require a taller piston to maintain a reasonable Compression Ratio. The result of the longer stroke on the 400 motor will be higher torque at low RPM.

The cylinder walls on the 351M/400 motors are adequate for most bore requirements, even up to +0.060" if necessary with a sonic check.