So i was wondering, what can i do to get more power out of a 351m?? i was thinkin new edelbrock carb because its more reliable then a holly, intake manifold, headers and exhaust obviously new plugs wires and distributer cap. But what should i be looking at to wake this thing up? help me out!

Thanks,
Zac

 

First carb reliability is based on the ability of the mechanic, a carb is a carb is a carb...variances are perpetuated by ignorance. Beyond that, no one or two parts will magically turn an engine into a fire breathing monster. That said, best bang for your buck is adding 50 cubes and throwing a 400 crank in there. Next best thing is a new bump stick. Then the standard bolt ons are carb, intake, headers, exhaust. A good set of heads are always nice as well. A standard tune up and you'll be sitting pretty.

 

Dual exhaust and propper tuning alone can have big gains.

beyond that, if I was going to open up the engine I'd do the following:

First, evaluate the need for machine work. I used to bore cylinders and recut cranks on every engine I got my hands on just because it seemed the right thing to do. I'm a little older now and more prone to re-ring and toss in a set of standard bearings if I can get away with it

Comp ratio is a good thing to focus on with these engines, TRW L2466F pistons are said to bring you to 8.6:1.

Even with the floppy factory 7.9:1 pistons you can wake this thing up with a fresh "zero and up" (RPM) cam grind and the timing gears set straight up. A set of headers helps, dual plane alum intake, a 600 cfm carter AFB type (edelbrock) or holley (i'm actually a bit of a holley guy).

Really though, the TRW 8.6 pistons, a modern idle to mid range cam, straight up cam timing, a decent intake & carb and I think you'd be very happy.

I do like the 400, but I kind of prefer the smaller displacement of the 351 for fuel economy. 50 less cubes of air/fuel at road speed RPM's..... It all adds up when the gas prices are so out of hand.

Here, read this for more details and background on your 351M


High Performance Options for the 351M/400 Engine .: Articles

 

FWIW...the 351M won't yield any better mpg's. If anything they'll be worse, less power trying to do the same work.

 

I've owned two 351ms and while no firebreathers, each had plenty of power to move a 4000lb truck around and a load the truck was rated for. By your logic, a 460 should get much better mileage than a 300 I-6. I agree with the basic premise that a larger more powerfull engine that doesnt have to work hard to move a heavy load will get better mileage than a smaller weaker one being maxed out but I dont think that applies here.

 

I'm going to be nice and just say that's not at all what I said and you must not be very familiar with the 335 series. I will say though, that if number of 335 series determines expertise, seeing as you had to qualify you statement with the number you've owned...I bet I'd be in the top 3 on the site of number of M/400's owned and built on this site. You do realize the 351M and 400 are the exact same engine, right? So what causes the mpg's to be so much worse in the 400 than the 351M??? Is it all the extra weight added by the different pistons...or is it the crank??? And I have to question your entire credibility on this topic if you're saying 149hp is plenty of power.

 

Before spending a cent on 351M heads, have them magnafluxed first, as they were very prone to cracking.

 

Ok then, what were you saying then?
Yes I realize the only dif is stroke. '
149 hp seemed plenty to pull boats, tractors, cattle trailers etc, my 300 I-6 pulled fine too, whats that, 110-120hp? Whats that do to my credibility?
I never said the 400 is going to get way worse mpgs but you wont convince me its going to get better either.

 

I agree, all else equal, a 400 will get about the same MPGs as a 351M in the real world. I understand the logic saying a 351M get's better .... but the real world tells me otherwise. Both come wityh low compression from the factory, both have good breathing heads (Cleveland) so maybe it's a matter of the heads better suited to the 400's longer stroke.

I will add for the person who may not realise it, changing a 351M to a 400 by putting in a 400 crank also requires eight 400 pistons. I know most everyone here knows that, but you never know who's reading these threads. Tim Meyer makes some great 400 pistons .... or you can get some compression using 351 C pistons and bushing the rod ends.

I'ld also suggest to the OP .... forget the headers if you have good manifolds. The Performer intake, a good carb, a straight up cam (not a wild cam either, a good torque grind maybe, maybe a Dual Energy 255 DEH or 265DEH) and ignition timing tweaking will help a lot .... but 8:1 CR is not a big squeeze?

 

So if you're going to get the same (potentially better) mpg's (which is ridiculous to be talking about in a 3 ton brick anyway) why not add the cubes and power to go along with it??? It would be stupid not to.

 

Well, I think the 351 is worth toying with.

The leverage of the 400 crank lends it as an excellent torque platform for a lot of low RPM lugging and for that reason I do think it's probably a more popular pick for truck duty (given a choice)

But I'm not going to tell a guy with a 351 that he can't make power or be happy without using the 400 crank.

Displacement is king but I believe it's the long throw leverage of the 400 crank that appeals to me more so than longer cylinder travel for more cubes.

Either of these engines are very nice given they both are allowed compression nearing 9:1, a sharp little cam grind targetting the bottom of the RPM range, likewise with the intake (dual plane) and properly sized carb with good overall tuning, especially with the ignition timing.

I too have had both 400's and 351's.

With an auto trans, yeah I really do like the 400 better.

Manual trans... well.... i think the manual trans helps you find that small MPG difference between the 400-351 displacements.

(just my opinion)

 

well for now im going to try to keep it on the cheaper side. Im not going to break into the motor right away if i don't have to. only if there turns out to be a major malfunction will i put a crank and pistons in it. For now im going to stick to bolt ons. so carb, intake manifold, headers, possibly take the heads and get them cleaned up and magnifluxed. But at some point i want to change the cam out because i heard that the tappet cam and the new age oil dont play together nicely

 

Oil has just gotten better, that's all. reasons to change cam would be wear or performance desires.

I'm on a lowbuck hunt for some power in a 351 I have in an f250 right now. I've made huge gains in hunting and eliminating vacuum leaks, adjusting carb, replacing a shot accelerator pump, ignition tuneup (plugs, cap, rotor, wires)

And, ignition timing.

Huge gains by just making the engine run as good as possible with the original equipment still in place.

Dual exhaust tomorrow (manifold back, I'm not a real big header fan truth be told)

 

i have regular manifolds on my 1996 5.0 f150, so ive never dealt with headers, i just feel like the '79 is a good canidate for headers, plus it seems like its easier to find headers for it then manifolds

 

best of luck.