Which is more directly related to Fuel Mileage?

[redneckgames]

Which is more directly related to mpg? Rpm or the distance from the gas pedal to the floor? This is probably a simple question but i am curious.

The reason behind this is that in my daily driver ( 88 1500 4.3 5 speed) on steep hills I have two choices on going up them on the highway. 5th gear will pull it at low rpm but the pedal is to the floor. 4th gear pulls it at higher rpm but with less pedal.



which way am I burning more fuel? Im guessing in 4th but it makes you think. Especially with the price of gas.

[Scotty_S-15]

That\'s a tough one. Logic would say in 4th gear, because a vacuum gauge would be showing higher vacuum as opposed to lugging it in 5th gear. But in reality, a tough call. Is that a computer controlled carb on your 4.3?

[redneckgames]

it is computer, tbi I believe? pretty sure

[racer1182]

in that situation 4th would take less cause of the pedal not being down as far and the motor not working as hard to go up the hill. Thats what I think but you may wanna get some more opinions.thats the way I have always thought

[speeder]

It takes the same amount of work to do the same job. With that said I think you need to look at efficiency. So if you are in 4th you are running more efficiently, but per minute you are burning more gas but also covering much more distance. In 5th you are much less efficient and for a longer amount of time, so you may be using a little less gas per minute, you are spending more time doing the same work with your foot planted.

I also think that 5th would waste more gas. Waste is the key word. I do not think that either would use much more gas than the other.

[riotpolice75]

ill agree that 5th is gonna use more gas. heres why. say you have a 10 mile long hill you go up that hill at 60 mph. the tbi motor has a throttle position sensor. in 5th gear you need to go up the hill at wide open throttle. the tps senses wide open throttle so its gonna command all the fuel it can get to hold that 60 mph. plus at wide open it kicks the computer into open loop operating mode. meaning your egr and o2 sensors are no longer used as inputs to the computer.



now in 4th gear to go 60 up the same hill say you need 1/3 to 1/2 throttle. yea, your turning more rpms but at half throttle the tps isnt putting nearly as much gas into the motor, therefore it runs more efficiently at say 3500 rpm in 4th gear than it would at say 1800 or 2000 rpm in 5th at wide open. also at a steady 3500 in 4th its in closed loop so the computer is still using the o2 sensor and egr to control fuel and combustion efficiency.



yeah...something like that.







smith

[adh383]

5 cents one way-----a nickle the other lol

[redneckgames]

Ha Ha. Does make you ponder on it though don\'t it? Especially with times like this.

[bratass]

Yea,what Riotpolice75 says makes good sense

[ChevyKiD_69]

if you ask me it would use more in 5th gear cause you are making it work harder to make it go the same distance then you would do in 4th not working as hard. reving is not always using more if you ask me. just my 5 cents. nick

[Indiana]

It is a matter of efficiency. Road load power = av + bv2 + cv3 (yes I am a math guy). Bottom line is that you are increasing the load by increasing the gravity. It requires more horsepower, which in turn is improved with more rpms. Just think of the rpm and torque curve. The closer you are to the two intersecting lines, the more efficient it is.

[HARDBALL]

Only problem is an engine is an air pump, so... at 3500 rpm you inject more fuel because of the increased engine speed and the computer tring to maintain a 12.7/1 mix under load.

Six of one...half a dozen of annother.........

[Indiana]

Good thought, Hardball. You air pump example is true, but a bit misplaced. It takes more electricity to run a compressor at 200 psi than 50 psi and the electric motor is more efficeint at a certain rpm. If you could place a monitor on the exhaust of his truck, you would have a ton more HC during a load at a lower RPM than a load at a higher rpm.

[MARKYMARK]

my boss had a 95 chevy fullsize pulling a 10,000 lb trailer over 1.100 miles when he drove at 85 mph we got one hour out of a tank of gas in drive. when he got tired and went to sleep i got 3 1/2 hours out of a tank in overdrive , but we didn\'t have the not anough power problem you have. his excuse was the tranny wouldn\'t be building enough presure at 2000 rpm to hold the convertor locked up. i said f--- it its under warranty and are gas bill would be outraiges when we got home. this was 10 years ago not last week, i would have got out and walked home.