I'd say pick up a 400 crank and rods. I have a 78 with 182,000 miles on it. The oil pressure is great at anything above an idle, but at idle the lifters will start ticking at a long light. I am in the process of building an engine for it. One of the things the machine shop is doing is putting in cam bearings with reduced oil supply, they claim this and a high volume pump will cure the oil pressure issues. The only difference between a 351 and a 400 is the stroke. You need the crank and pistons to stroke it out to 400. I just bought a set of 9.5:1 pistons from Tim Meyer for $235.00 that and the XE256 Comp cam should wake this sleeping dog up (has an unknown RV cam in it now).

 

Woodcrafter said it best. I love my 351M. It runs great, no problems, BUT I am currently pulling it out and swapping it for a 400 which was police towed in off the street and unclaimed with a FRESH rebuild. (Lucky for me, sad for the guy who rebuilt it!)

 

My dad has a 351M in his 77. It has 47k on it since rebuild. We were going down main street and he told me to stomp on it...nothing, didn't even put you back in your seat, didn't feel like anything. I can light up 34" super swampers at a stop sign no problem though.

Defiantly not one of my favored power plants, but it's alright.

 

If you're looking to rebuild anyway, there's nothing wrong with going to the 400. The oil pressure problems are to be assumed if everything is left exactly as stock. If, however, you look at Tim Meyer's website, there's an entire article written about how to change the 400's oiling characteristics by making a few changes during the machining process. Using a high volume pump alone may pose issues by forcing all the oil up, but not giving it the ability to flow throughout the block appropriately. The 335 forum is a good location to find a lot of discussion about the 400 and its inherent issues.

Myself, I've got a 400, but Tim and I have spoken, and as soon as money allows (which will be in the next couple months), I'll be going with his 434 stroker kit, and CHI heads. I'm also going to be going with a roller retrofit, and choosing pistons to settle on about a 10.5:1 ratio. With regard to the oil pump, even with that setup, Tim said that a stock oil pump would still be adequate as long as the steps were taking during the machining process, to improve oil circulation.

My dad kept hammering on me about a 460, as I have one in the shed that's been massaged up to around 550 horse, but I'm being stubborn about this. While I know it won't be original, the plant in my truck will still be 400 based, as the 460 never came on any 79 4x4. That, and I like the idea of being at a couple car shows, and guys looking under the hood and saying, "Oh, it's just a crappy 400", which will make my evil grin come out. Granted, the CHI heads, ceramic coated headers, and other little shiny implements might make them think twice, but it's the thought that counts.

When Tim said they got 530 horse, and 510 ft/lbs of torque out of a 434 on plain old pump gas, I knew that was the plan for me. That plant was EFI, and mine will be carbed, so I don't expect the same numbers, but still...it'll have enough grunt to scare the natives.

 

Another thing about the 335 series engines (351-400) is that their oiling system is the same design as the 385 series (429-460). No parts of the oiling sys. will interchange, but it is routed the same.
These mods originated I believe from the high winding 351 Clevelands, which would spin bearings and all kinds of nasty stuff at sustained high rpms. They also used to mod the oil pumps with a 100 psi spring.
I'm not saying not to do oil mods, the above listed ones are excellent and recommended for both the 335's and 385's from what I hear.
Another easy mod-it may not look pretty but makes alot of sense, is to run a external high pressure line from the plug above the fuel pump to the rear oil press. sending unit to feed the rear of the engine.
Other than that, a windage tray will help, and of course a bigger oil pan never hurts.
Best off to check the 335 forums, or do searches on 351c's, there's alot of info available here and there.
I too have seen many high mileage 351m/400, some keep going some grenade-depends on maintenance and abuse.
These engines biggest problem is the detuned smog carb and lame cam, and plastic/nylon geared timing chain-and the bad rep. they have recieved from the smog and oiling stuff.
There is an article out there where a guy made 380hp, 468 lbft with a 2 barrel carb 400 using exhaust manifolds.
If I didn't have a bigblock, I would have a 400 or 434 in my truck, and still would like to build one some day.

 

Personally, the 351M was not one of Ford's better ideas. Low hp, low torque, oiling problems, & short life span are just a few of the negative things. If it's a daily driver/grocery getter, nothing wrong with leaving it that way. If you're looking for a tow rig, or an off road beast, toss the 351M in favor of a 400, or better yet a 460. The 400 is much better in the torque dept than the 351M, and responds much better to mods than the 351M. I'm not trying to rain on anyone's parade, but these are just the facts.

 

Hell no i aint happy w mine. Its sittin in the shop while the truck is under the pole barn. I just replaced the crank, oil pump and mains about 3 weeks ago w 135K miles(due to crappy oil pressure). now three weeks later it sputtered to a stop in the middle of town with a broke cam shaft(leaving me to be towed through town by a 6cyl F-150) . Dang thing broke at the first bearing clean in half.
But when it ran.. It was about a truck length slower than my buddies 95 Mark LT w a 302 K+N cold air and throttle body.
And it hauled 1000lbs and 1500lbs loads of scrap w no problems.
Now my 800 dollar engine rebuild is costin me on min wage and when itll run again itll b the normal 10mpg or so.

If you get one.. dont dog it, REBUILD IT first. Low oil pressure= rebuild everything.

 

I personally dont have a use for them. As mentioned before they are good motors and pretty reliable but their low horsepower/torque/oil pressure make them not for me. There are always upgrades (cam 4bbl intake headers etc) but if youre going to be buying that stuff you might as well buy it for a 460. Gas mileage is also extremely similar between the two...especially once you start minor upgrades.

rebuild kits and aftermarket parts cost relitively the same for 351Ms vs 460s. The only difference would be the price of a junk yard 460. Around here complete engines go for $200-250.

X2 with running the 351m now while you build a 460.

 

My 351M has lots and lots of miles on it...and keeps on running. Oil pressure isn't great, but isn't terrible either.

I don't drive it much, but it always fires up and goes wherever I point it to!

 

My 351M died a about 2 months ago. I'm not knockin' the engine, it did fine but now it's dead. Had a burnt exhaust valve in #8 and #2. #2 also burnt the webbing between the cylinders. It's now a boat anchor. It always had low oil pressure, around 10 psi or so warmed up. I was almost impressed with the fact that the engine with burnt valves and all, almost passed AZ emissions. It ran pretty decent too, even with the burnt valves. I tried leaning that ******* out (which probably burnt it a little more) but in the end I couldn't pass emissions.

So I'm going 460. I got it for next to nothing. Seems to be a fresh rebuild, but you never know until you start it up to see what you bought. Just keep in mind that it may have been cheaper to stick with the 351M/400 by going with a rebuilt engine, as all the little piece for the 460 conversion add up quickly.

The aftermarket does not support the 351M/400 very well. There are performance parts for the M, but not in the quantity as a 302 or 460. And to be fair, the 351M/400 wasn't around long enough, and it was introduced when there was increased emissions standards.

TMyers Inc. does some incredible stuff with the 400's.

 

I have a 351m in my 1979 100 it currently runs on lp gas (propane) the heads are slightly modifyed and it has a larger cam and headers and runs absolutly fine 170+ks five days a week. Oil pressure is not a problem and the motor is approaching 300 000k's! Maybe the aussie m series are different?

 

I'm very happy with my 351m, it has 134,000 miles on it and the oil pressure is fine, although I don't know where it's really supposed to be and I don't look at it that much, I've never seen it below 15 and I've aeen it as high as 70.

 

I had a 67 that had a 351m in it. PO had installed it with a 4 speed. I had the same problem with oil pressure. I switched to 20w50 oil and saw my pressure pickup. 0 p.S.I. @ idle, 20 @ 65 mph after 20w50 20 p.S.I. @ idle, 40 @ 60 mph. I did not like that motor.

 

I have 4 77-79's w/ the 351m in them and they have not let me down, I was travelling at 65mph, towing a 69 GTO on a car trailer approached a bridge w/ a pretty good incline to it and I was able to gain speed up the bridge, it is a 79 s/s 4wd man trans, 350 gears w/ 33's and the gas mpg really ain't that bad considering that it has a slight cam and a 4bbl carb. I had the 460 and I have the 400 in other trucks and for the utility purpose the I use them in, I am really happy w/ them all, well honestly there is an issue w/ the carb on the 78 bronco, nothing a new or re-build won't fix.

 

OK, so what causes the oil pressure to drop after 100,000+ miles? is it because of oil pump wear? is it because the oil galleys / tubes / etc in the block fill up with gunk (kinda like calcium build-up in your heart lol)? if this is the case, why not run some Sea Foam in the oil for a few thousand miles hopeing the engine "cleans itself up" on the inside and hopefully oil pressure returns. BTW SeaFoam does the trick!