Ok guys, I bought a remanufactured 400 for my '77 f-250 from S&S engines(before I found this web-site). I called and ordered the motor and they told me they had one ready to go w/ an RV cam and could have it to me in 3 days. I thought more torque couldnt hurt "send it to me".

I Don't know a whole lot about camshafts but here are the specs:

Cam Lift:
Intake= .281
exh. = .296

Valve Lift:
Int. = .486
Exh. = .512

Sae Duration:
int. = 282
exh = 292

.50 Duration:
int. = 204
exh. = 214

I put an Edelbrock Performer intake and 1406 carb w/ headers and a Single 3" highflow exhaust. Boy did that wake it up. I am only getting about 10 Mpg. Does that sound about right. Is that too much cam?

P.S. 4x4, c-6, 410 gears.

 

thats a decent cam...i would guess it has something to do with your rear end ratios

 

You're running almost the exact same setup as I am, and I get 9 - 10 depending on the phase of the moon. My 400 is in a '72 F-100 4x4. C6, 4.10s, NP205, 35" tires. It doesn't matter if I goose it at every green light or baby it along, it gets 9 or 10.

 

The shape of these truck (like a brick) dictates gas mileage. Regardless of whether the truck has a 302 or a 460, city gas mileage will be about 8-12 at best. Changing the rear axle ratio to 3-1 won't help much, in fact, it might lower the city gas mileage, because it will take more gas to get it to move.


With a 3-1 rear axle ratio, your highway mileage will improve..somewhat, about 2-3 more MPG.

 

regardless of CID? i believe not...

"Changing the rear axle ratio to 3-1 won't help much, in fact, it might lower the city gas mileage, because it will take more gas to get it to move."

i am sorry sir but your theory is incorrect....that is that

 

Theory? If you move the gearing to the point where you're at 3/4 throttle just to keep up with traffic while leaving a stop light, then you're wasting a lot of fuel.

 

Numberdummy is right.
my 390 F250 with 4.11 gears gets the same to better milage than my old 390 F100 with 3.55 gears. Thats not to say there is other factors involved, but with the low gears, I don't need to give it much gas to get up to speed. The CID of an engine has only a minor effect on economy. a 302 that needs 6in. of vacuum to push it down the highway will always get worse milage than a 460 with 20in.

 

the fight is against RPMs, with a numerically lower gear ratio the vehicle will move faster at a lower RPM.....

perhaps i am wrong, what method are you all using to measure mpg?

what are your rpms at 60mph?

aerodynamics does have significant effect on economy...

 

True RPMs have a factor in economy also. Not to dork out too much, but this is the way I see it. For any set speed and load...

Fuel consumption = RPM * Displacement * manifold vacuum

so numerically high gears will make rpm go down, but manifold vacuum go up, so it is close the sort of cancel each other out. Same with displacement, if displacement goes down, again manifold vacuum will go up.

The biggest factors in economy are rolling resistance, weight and the effeciency of an internal combustion engine to convert fuel to energy. Bigger dispacement engines are a minor factor in economy because they are part of rolling resistance and weight. Gearing is important too. Gears should be used so your engine is operating at its most effecient RPM. There is a huge tradeoff with gearing also. low gears may allow for better towing and city economy, but highway driving would suffer.

Again, just my 2 cents, but hope this helps!

 

Thanks for the input guys. I will be looking to do an AOD swap or gear venders in the future as I plan on having this truck for a long time, but those are both very expensive. The extra gear sure would be nice!



https://www.ford-trucks.com/user_gal...?albumid=29415

Here is what she looks like so far^

 

Looks nice! fwiw. I see you're non emissioned. An EGR valve can net ya 1 more mpg. Not really worth the effort to turn back, though. You have larger tires, I suspect you want a steeper gear to get up to speed quicker. Higher gears and bigger tires makes for lots of gas-pedal effort to get up to speed. But the lower cruising rpms at highway speed makes for nicer mpg....and easier on the ears,lol. I have a 78 f150 w/36x14.5's and 3.50 gears. I ditched the C6 and put a np435 in. I use the granny low to get the speed up quickly, but I still cruise at decent rpms. It's not a powerhouse by any stretch though. I guess I don't really have a point here, do I?

 

everybody is right...or so it appears to me...except that formula...can't be 'mathed' out like that but we all know the big elements... how much air-fuel (volume) is pumping through and how efficiently is it being turned into energy and how is that energy being manipulated for speed/movement.

Gears, weight of rig, cid ....and the weight of the foot have much to do with the volume being sent through the engine. The aerodynamics will have little effect in city and much more at hwy. Weight will have far more effect in city. Gears are darn near everything when it comes to what we can do to influence economy....the best option if your rig is a daily driver and you plan on keeping it is to buy a gear vendors over/underdrive and keep your low end gears for city/hills and have a final drive of 2.7 or so for hwy....then slow down on the hwy and the the brick design won't be so damning...also following a semi....safely... can net 20-30%..as proven on myth busters.

The 'build' and maintenance will determine the efficiency of the engine. Vacuum is nothing more than a measure of the volume your using...to include fuel use it to learn how to drive more economically. then, maximize your build when you rebuild...open up the exhaust a bit and build for the rpm you will run at most often..try to get as much compression as you can for your weight, use etc..quench helps a ton...a 400...for example can give you a very flat torque curve which will help you get going with less volume and if geared right..can cruise along nicely with the torque to pull it off at a lower rpm.

A 302 will not be able to do that with the same heavy rig but can with a 3000lb car etc.

I'm playing with the near worn out 460 i have in my new '79 bronco...it has 350 gears and when i drive it conservatively....55 hwy i bet i get about 15...but city and when i drive 65-70 I'm watching the guage sink into my wallet....I'm officially testing it now and will see. This bronco was rode hard and put away wet for sure but it's fun for me and my bird dog to ride in without the top. Makes august livable.

 

This is correct. My EFI 434 gets 15+ MPG on the highway. I have 3.25:1 gearing and low rolling resistance. My torque curve is nearly flat from 1500 RPM through 4700 RPM. Carburators are not very efficient at part throttle operation, but a Mass Air EFI system is. I run very close to 14.7:1 air/fuel ratio, unless I go to WOT where it becomes richer.

Maximum fuel economy can be achieved by keeping the RPM in the 'sweet spot' (maximum torque) of the cam. A well built motor will extend the RPM range of the usable torque curve. Increased compression will raise the whole torque curve and low valve overlap will help at low RPMs.

 

My old 71 f-150 2wd 302-C4 went from 12-13mpg to 15-16mpg with only a gear change from 3:50 to 3:00.It still towed my Must on an open trailer OK.

 

i would still like to know what method you people are using to measure your MPG