Another fuel mileage debate...

[propanemudtruck]

Hello guys,

My 90 Chevy is a shortbox regular cab, 350 TBI, 700R4 (lockup not hooked up yet) and 3.42 gears. I've got a front and back plow on it and drive 50-55 mph to work. The only way to really tell is to try this out, but I have a theory yet to be proven.

http://www.fueleconomy.gov/feg/driveHabits.shtml

This link says overdrive always helps because it lowers engine rpms. I agree, in a passenger vehicle. BUT if the engine drops below a certain rpm with so much weight, would it be better for me to leave it in drive instead of overdrive? It seems more responsive and the truck isn't lagging as much.

Any input?

I assume the plows add another 600-900 lbs with all the heavy brackets, pump, valves, hoses and whatnot.

[Josh]

Most engines at higher RPMs while cruising produce more power than is being consumed by the vehicle to move it along. A V8 will almost always get better gas mileage the lower you can keep engine speed, however, that is assuming there is enough torque output at that rpm to maintain vehicle speed. I'd try it both ways for a tank or two and see what works. What you wanna do is try to keep it in it's sweet spot of volumetric efficiency/peak torque.

[propanemudtruck]

Right. I know a stock TBI 350 is no power monster but it runs pretty good. I still don't understand why my TBI blazer had so much more pickup and response with the same gears.

I figured next tank I'll try a run with just drive and see how it goes. W/O any extra weight of plows, the truck usually gets around 15 mpg. W/ the wind wall and weight added on, I figure I'll be about half that. So anything to get it any better will yield higher profit at the end of the season.

[Prerunner1982]

Is is necessary to drive 50-55mph to work?

I was able to get 20mpg out of my Jeep Cherokee just by driving 40mph to and from work instead of the posted 45-50mph. And of course ease in and off the gas as well. It isn't fun to drive mileage conscious.

[Fursphere]

Originally Posted by Prerunner1982

Is is necessary to drive 50-55mph to work?

I was able to get 20mpg out of my Jeep Cherokee just by driving 40mph to and from work instead of the posted 45-50mph. And of course ease in and off the gas as well. It isn't fun to drive mileage conscious.

Here in California you'd get run off the road for driving under the posted limit.

[special-K]

Your truck should be able to pull 1,000# w/o affecting it's power so drastically that it can't run at hiway speed in o/d within a proper rpm range.In my '92 I use 50 mph as the divide between using o/d or straight drive.I'd say I use more fuel running 45 in 4th that 55 in 5th.I'm sure I use less fuel at 50 in 5th than in 4th.

[propanemudtruck]

I drive about 11 miles to work, but I've got many miles of driving in my plow route once snow hits. The weight isn't so bad, but keep in mind I loose all aerodynamics if there was any to begin with a scooped wall in front of the grille.

40 mph isn't possible on a 55 mph road and I keep in mind if someone's behind and I'm under the limit I'll kick it up a bit.

But thanks for all the input

[raycow]

There are two reasons why taller gearing saves fuel. One is the expected saving that results from reduced engine and accessory frictional losses. The other is that engine operation is more efficient at larger throttle openings. You save power on the intake stroke because you are pulling the piston down against less vacuum. I know this sounds trivial, but laboratory tests have shown that the saving is measurable.

Naturally, your fuel delivery system has to be calibrated properly for this to work. If the mixture goes too rich you will lose what you gain. Computer controlled injection in modern engines makes it easier of course, but it can still be made to work even with a carburetor.

Ray

[propanemudtruck]

I read something similar in one of the last few diesel magazines I read, there was a column like 50 reasons a diesel is better than a gasser and one reason is there is no such thing as running lean (it'll just stall) because there is no air flapper or butterfly on the intake just fuel modulation. The gasser has to fight to get air on every stroke and overcome that butterfly (creating vaccum)...

[raycow]

Originally Posted by propanemudtruck

one reason is there is no such thing as running lean (it'll just stall) because there is no air flapper or butterfly on the intake just fuel modulation. The gasser has to fight to get air on every stroke and overcome that butterfly (creating vaccum)...

You are absolutely right. The working fluid in any internal combustion engine is mostly air. The fuel contributes relatvely little mass or volume. A diesel gets a full charge of air on every intake stroke, while a gas engine gets a full charge only at wide open throttle.

Ray

[Prerunner1982]

Originally Posted by propanemudtruck

40 mph isn't possible on a 55 mph road and I keep in mind if someone's behind and I'm under the limit I'll kick it up a bit.

It's called a speed limit not a speed requirement. If they are in so much of a damn hurry, I will give them ample opportunity to go around but until they pay for my gas I will be damned if someone else is going to dictate how I drive.

I get what you are saying though....

[Psycho71]

Originally Posted by Prerunner1982

It's called a speed limit not a speed requirement. If they are in so much of a damn hurry, I will give them ample opportunity to go around but until they pay for my gas I will be damned if someone else is going to dictate how I drive.

I get what you are saying though....

Another reason I don't like going to Oklahoma. And probably why you cuss us Texans.

[Prerunner1982]

Originally Posted by Psycho71

Another reason I don't like going to Oklahoma. And probably why you cuss us Texans.

Yeah.. we are smart enough to allow more than enough time to get to where we are goin'....

[special-K]

Plows will kill your aerodynamics and effect mileage...true.But,when I plowed I only had the plow mounted when out to plow.The fuel consumption going to between jobs was excellent compared to while plowing.