PDA

View Full Version : Gas mileage 460 vs 351m


Rico
09-28-2010, 04:45 PM
I have a 1979 F-150 4x4 and I wanted to make up my mind on swapping in a 460 or keeping the good ole 351m in it. But my question is why do these two engines with about 109 cubic inches apart have the same gas mileage? This is really stumping me.:icon_confused: If any of you guys can help me confirm this I think I'm gonna go with a 460 in my truck especially since I plan on bigger tires and off-roading a lot with it.

adsm08
09-28-2010, 04:54 PM
More available power means that the engine has to do a lower % of its maximum work to do the same job. Less work means less fuel.

The 351M is kinda nerfed by emissions crap and a less than wonderful design. It has a long stroke and low compression (for emissions) which means it needs more fuel to give the same power. The 460 doesn't have that issue.

GoodOld85BlueBalls
09-28-2010, 05:03 PM
You want a 460 and your worring about fuel mileage???
:icon_rofl::icon_rofl::icon_rofl::icon_rofl:
Just shoehorn it in, this I gotta see in a Ranger!!!!
Im thinking..........BUILD THREAD!!

Rico
09-28-2010, 05:18 PM
I'm thinking about the power advantage not the gas mileage crazy.:annoyed: If the gas milage is the same then why not go for the bigger motor?

country0001
09-28-2010, 05:27 PM
should be bout the same

02RangerXLT
09-28-2010, 05:58 PM
460 and gas mileage shouldn't be in the same sentence... our F250 probably got 8mpg empty... 5 or 6mpg pulling a trailer... yeah, I don't care what you put it in, the 460 is a gas hog.

The purple one
09-28-2010, 06:07 PM
I had a 1978 F150 4X4 super cab with the granny 4 speed way back when. It had the 351 M and I could get 15 MPG on a very good day empty. That truck would pull down a house too.

adsm08
09-28-2010, 06:16 PM
I had a 1978 F150 4X4 super cab with the granny 4 speed way back when. It had the 351 M and I could get 15 MPG on a very good day empty. That truck would pull down a house too.

The 351M isn't a bad engine, but it doesn't hold a candle to the Cleveland, the Windsor, or the 460

COPPERHEAD85
09-28-2010, 06:30 PM
460 with a after market timing chain and gears.
Parts are pretty cheap believe it or not,in the process of building one myself,still in the collecting parts and research phase.

2.9XLT
09-28-2010, 07:26 PM
460 definitely, it'll get the same gas mileage as a 351m, and make more power. Plus performance parts are a lot easier to find.

feellnfroggy
09-28-2010, 08:08 PM
Same as the expeditions with the 5.4l and the 4.6l the 5.4 gets better mileage. Just like running too high of a gear, 5th when 3rd will do. Your dumping a bunch of extra fuel to get the work done, and its being wasted. but seriously your talking about a 351m (which is basically a small block 400) and a 460. Why the hell has gas mileage even crossed your mind? Think of shuttle launching into space when you think gas mileage.

adsm08
09-28-2010, 08:45 PM
460 with a after market timing chain and gears.
Parts are pretty cheap believe it or not,in the process of building one myself,still in the collecting parts and research phase.

Talk to 7.5_STX. He's managed to cram a 460 into his 91.

Boggin
09-28-2010, 08:54 PM
if i were you id keep the 351M. it will be just as good on gas or better, and unless your looking for a shit load of hp your wasting your time and effort. alot of people bash the 351m but i love mine and would not trade it for a 460 for the world

The 351M isn't a bad engine, but it doesn't hold a candle to the Cleveland, the Windsor, or the 460

your kidding right? my 351m will tear up a 351w like a freakin 2.9 lol

Boggin
09-28-2010, 08:55 PM
Talk to 7.5_STX. He's managed to cram a 460 into his 91.

i have a buddy who is currently cramming a built 429 in his 2nd gen, hes t120r on here but i dont think he posted yet

85_Ranger4x4
09-28-2010, 10:06 PM
460 definitely, it'll get the same gas mileage as a 351m, and make more power. Plus performance parts are a lot easier to find.

Dunno about that, stroker kits are pretty common for a 351M... all you need is a crank and pistons out of a 400. That is a heck of an engine.

Same as the expeditions with the 5.4l and the 4.6l the 5.4 gets better mileage. Just like running too high of a gear, 5th when 3rd will do. Your dumping a bunch of extra fuel to get the work done, and its being wasted. but seriously your talking about a 351m (which is basically a small block 400) and a 460. Why the hell has gas mileage even crossed your mind? Think of shuttle launching into space when you think gas mileage.

Same with the 4.2, 4.6, and 5.4 in the F-150, they all get about the same :icon_confused:

Even a 302 in a fullsize doesn't get much better milage than a 460, mid teens vs low teens.

AllanD
09-29-2010, 11:12 AM
I think the 351w is a wonderful engine... in a Mustang or ranger with someone who undrstands that
revving it is a bad idea.

a 351 is to a 302 EXACTLY as a 4.0 is to a 2.9


a 460 built to about the same performance level will generally get better mileage
because to produce the same power it'll generally be spinning at about HALF the rpm.

My brother through careful setup managed to get his 1989 F250 with a 351W engine to get a fairly consistant 16-17mpg on the highway, otoh the 460(EFI) he replaced it with could usually do 18-19 on the identical (repeated) trip.

but when it came time to tow something the 351w had NOTHING when compared to the 460.... it came as no suprise that towing anything he ever tried ever knocked down the mileage of that 460 below ~14mpg

I say go with the 460, it's simply a better engine.

Hell, I have an idea of putting a 460 into '92-is F-150 with ~3.08 or 3.55 gears

the idea being that grinding across nebraska in 5th gear with the engine turning over
~1600rpm... not built for power, but minimizing the operating rpm in cruise.
it takes about 85-90 road hp to keep an F-150 rolling at 70mph the engine that can do that at the lowest rpm wins.

And the only real competetion to a 460 set up "correctly" is a 4.9 inline 6cyl, but I know from
experience that one of those isn't a whole lot of fun driving westbound across nebraska into
a 30mph headwind.


But I was also going to run it on the MAF EFI system robbed off a 1995 5.8
and since the 460engine I already have has flat top pistons in it, with the EFI heads
the compression will be "up there"

high compression, low rpm

Generally speaking the largest practical engine when geared to allow low rpm operation will usually get the best economy.


It should be noted that while all the people who really know me KNOW "Agressive" is an understatement,
yet I've always been the one who winds up in the drivers seat of "their baby", especially
when getting either the maximum ammount of miles behind the receiver hitch OR towing
something heavy and/or not arriving in an ambulance are the goals of a trip.


AD

feellnfroggy
09-29-2010, 11:38 AM
Allan remember the lowest rpm in theory is nice for mileage, but you dont wanna bog it either, carbed or fuel injected the air/fuel ratio leans out higher in hte rpm range, so a truck with 460 cruising at 1200 rpms at 70 and a truck with 460 cruising at 1800 rpms at 70. The truck with 1800 rpms will have the slightly better mileage. Its a balance thing as well. But your right about the bigger engine having better mileage just dont go too low in the rpms.

WTF
09-29-2010, 02:38 PM
It's a 79 F150 he's putting this thing into- screw mileage! It's like a brick sh*t house going down the road. What's wrong with your 351M? If nothing than I'd just spend money on upgrading it instead of starting over with another engine. My brother did a stroker kit on his 351M, milled the heads, cammed it, stall convertor in the C6 and that truck would roast all 4 tires (35" ground hawgs + 4 low) on dry pavement.

Mileage out of a big block? That's like taking the noise out of a Harley v-twin.:beer:

adsm08
09-29-2010, 04:41 PM
Just like running too high of a gear, 5th when 3rd will do.

Dude, that would make it knock like a pair of Jehovah's Witnesses.

85_Ranger4x4
09-29-2010, 06:29 PM
My milage went down in my F-150 when I lowered my rpms, with my tiny stock tires I could just about hit 20mpg pretty easy. Now 16 is the norm. Putts down the road at 1400 rpms and downshifts on almost every hill with the cruise on.

adsm08
09-29-2010, 06:33 PM
And what size tires did you go to without re-gearing?

COPPERHEAD85
09-29-2010, 06:37 PM
if i were you id keep the 351M. it will be just as good on gas or better, and unless your looking for a shit load of hp your wasting your time and effort. alot of people bash the 351m but i love mine and would not trade it for a 460 for the world



your kidding right? my 351m will tear up a 351w like a freakin 2.9 lol

Come on down big guy............My little F-100 will be waiting on ya!
Just yanking your chain Boggin.........dont get you knickers in a twist....lol.

85_Ranger4x4
09-29-2010, 07:33 PM
And what size tires did you go to without re-gearing?

235/70-16's to 255/75-17's with 3.31 gears. It still drives fine, but regearing to 3.73's in the works. My Ranger needs an engine worse. So until then, the stock wheels with more stock sized tires (255/70-16's) get swapped on when I need to pull something.

I snagged the wheels with 265/70-17's cheap and thought I would give them a whirl figuring if I didn't like it I could turn around and sell them for a profit. They were not that bad, and I found a set of new tires cheaper than I could find a set of 16's so they stayed. I don't drive on the highway much anymore, so the decreased hwy milage isn't a big deal for me.

It is an extreme case, but shows that the lowest possible rpm doesn't always yield the best milage.

Boggin
09-29-2010, 08:16 PM
Come on down big guy............My little F-100 will be waiting on ya!
Just yanking your chain Boggin.........dont get you knickers in a twist....lol.

haha, im sure yours is running a bit better than the one i tried

AllanD
09-30-2010, 12:55 AM
My milage went down in my F-150 when I lowered my rpms, with my tiny stock tires I could just about hit 20mpg pretty easy. Now 16 is the norm. Putts down the road at 1400 rpms and downshifts on almost every hill with the cruise on.

Every engine has it's "happy zone"

I can say that an F-150 with a 4.9, 5sp & 3.08's will NOT get as good mileage as the same truck after you regear it to 3.55's.

That is presuming stock or close tires.

an F250 with the same combo and stock 235/85-16's 3.55's is too much gear, it needs 4.10's.

The point of the big engine is all about reserve torque and in terms of "happy zone" the 300/4.9 and
the 460/7.5 are remarkably similar in their best mileage rpm band.

I'm still looking for the proper body and frame. Ideally a 1992-95 F-150 supercab "glider"
(No (or dead) engine and trans)

I'm pretty much convinced that I can hid 100gallons of fuel tank in it without counting
my (commercially made) 70gallon in-bed tank



AD