Using OVER DRIVE saves gas?

[silverpig]

Originally posted by: Eli

Originally posted by: JEDI

Originally posted by: Eli
Wow.....

I'm going to be nice.

Basically, you do not understand the way things work. 😉 Overdrive means that the transmission is in a gear that provides more than a 1:1 gear ratio, typically around 0.8:1. That means that the engine only has to turn 0.8 times to turn the output shaft on the transmission once.

This will save you fuel, because you are at a lower RPM for a given speed.

For example, if you are crusing along at 65MPH @ 2500RPM, and you hit the overdrive button, your transmission will shift, and your RPMs will drop to, say.. 1800RPM. You will still be going 65MPH, but you will be using less fuel due to the lower RPMs.

In short, speed has little to do with MPG at cruising speeds. It only takes a few tens of horsepower to keep a car moving along at 60MPH.

so why not use a gear with .01:1 ratio. wont that boost mpg thru the roof? (ok, make the gear out of antamantium so it wont break.)

also, speed has little to do w/mpg at cruising speeds???

so i'm using almost the same gas at 90mph as i am at 65mph?

Because engines don't have enough power at 150RPM to move the car forward at 65MPH. 😉

And.. MPG is fuel usage over time. So yes, of course you are using more fuel at 90MPH than 65MPH. You're also traveling 25MPH faster. Whether this will result in a net gain or loss of overall MPG depends entirely on your car and driving conditions.

You'll most likely get less mpg the faster you go. The air friction at 95 mph is much greater than at 65 mph.

 

[Howard]

Originally posted by: Eli

Originally posted by: JEDI

Originally posted by: Eli
Wow.....

I'm going to be nice.

Basically, you do not understand the way things work. 😉 Overdrive means that the transmission is in a gear that provides more than a 1:1 gear ratio, typically around 0.8:1. That means that the engine only has to turn 0.8 times to turn the output shaft on the transmission once.

This will save you fuel, because you are at a lower RPM for a given speed.

For example, if you are crusing along at 65MPH @ 2500RPM, and you hit the overdrive button, your transmission will shift, and your RPMs will drop to, say.. 1800RPM. You will still be going 65MPH, but you will be using less fuel due to the lower RPMs.

In short, speed has little to do with MPG at cruising speeds. It only takes a few tens of horsepower to keep a car moving along at 60MPH.

so why not use a gear with .01:1 ratio. wont that boost mpg thru the roof? (ok, make the gear out of antamantium so it wont break.)

also, speed has little to do w/mpg at cruising speeds???

so i'm using almost the same gas at 90mph as i am at 65mph?

Because engines don't have enough power at 150RPM to move the car forward at 65MPH. 😉

And.. MPG is fuel usage over time. So yes, of course you are using more fuel at 90MPH than 65MPH. You're also traveling 25MPH faster. Whether this will result in a net gain or loss of overall MPG depends entirely on your car and driving conditions.

An engine is almost guaranteed to be less efficient at 150RPM than at 1500RPM.

 

[Eli]

Originally posted by: silverpig

Originally posted by: Eli

Originally posted by: JEDI

Originally posted by: Eli
Wow.....

I'm going to be nice.

Basically, you do not understand the way things work. 😉 Overdrive means that the transmission is in a gear that provides more than a 1:1 gear ratio, typically around 0.8:1. That means that the engine only has to turn 0.8 times to turn the output shaft on the transmission once.

This will save you fuel, because you are at a lower RPM for a given speed.

For example, if you are crusing along at 65MPH @ 2500RPM, and you hit the overdrive button, your transmission will shift, and your RPMs will drop to, say.. 1800RPM. You will still be going 65MPH, but you will be using less fuel due to the lower RPMs.

In short, speed has little to do with MPG at cruising speeds. It only takes a few tens of horsepower to keep a car moving along at 60MPH.

so why not use a gear with .01:1 ratio. wont that boost mpg thru the roof? (ok, make the gear out of antamantium so it wont break.)

also, speed has little to do w/mpg at cruising speeds???

so i'm using almost the same gas at 90mph as i am at 65mph?

Because engines don't have enough power at 150RPM to move the car forward at 65MPH. 😉

And.. MPG is fuel usage over time. So yes, of course you are using more fuel at 90MPH than 65MPH. You're also traveling 25MPH faster. Whether this will result in a net gain or loss of overall MPG depends entirely on your car and driving conditions.

You'll most likely get less mpg the faster you go. The air friction at 95 mph is much greater than at 65 mph.

I know.... I was just saying. We're just pulling numbers out of our asses, and there are too many variables.

 

[Eli]

Originally posted by: Howard
An engine is almost guaranteed to be less efficient at 150RPM than at 1500RPM.

I'd say this will depend on whether the engine was designed to run at 150RPM or not, but yeah, probably.