some of you guyz are missing the point.

Here's another way to think about this.

you are on level ground traveling 47mph - with the cruise control on - and lets say you are running a constant 1500rpm.

Then the road changes and is no longer flat, now uphill at 10 degrees (but not enough of a grade increase to require a downshift). Something will need be changed or your car will start to slow down.
Your cruise control will maintain 47mph and the 1500 rpm, but to do this it will increase the throttle plate opening to maintain the 47mph. All that changed was the amount of the throttle plate opening . You're still running 47mph and 1500rpm (same exact amount of explosions/minute) - but now it takes more fuel to maintain the speed beacuse of the uphill grade.

when going from 5th to 6th, sure the RPM lowers. But since 6th gear takes you further out of the engines power band and reduces mechanical advantage - it now might take more throttle plate rotation to maintain the 47 mph then it did in 5th gear (but 6th has reduced the amount of explosions per minute).

So it's a trade off. You reduce "explosions per minute" when shifting from 5th to 6th gear, but it takes increased throttle plate opening to maintain the same speed (or engine power) because of the reduction in mechanical advantage and beign even further from the engines powerband.

Try this same example at 65mph and things change, more in favor of 6th gear. The engine RPM will be higher due to the -now- 65mph speed, and the engine becomes more powerful as its nearer the powerband. And this increased power (due to the higher rpm @ 65mph) helps overcome the mechanical dis-advantage caused by shifting into 6th... and not as much of an increase of throttle plate deflection is needed to maintain the speed.

Explosions per minute is only half the equation. The other half is the amount of fuel needed to give a powerful enough of explosion to maintain speed.

And because explosions per second are only half the equation - then it matters at what engine RPM the MPH is trying to be maintained, and the degree of mechanical dis-advantage caused by shiftign into a higher gear. In the powerband, a little more AF mixture causes more power increase than the same amount of throttle plate rotation at 1000 rpm.
And a higher numbered gear - causes mechanical dis-advantage - and more throttle plate rotaion will need be made to compensate.

Remember, "14.7:1" is the ratio of air to fuel... not the amount of that combined mixture flowing into the cylinders.

Shifting from 5th to 6th gear mimicks the same change as -now- going uphill from a once-flat road. At some MPH/engine-RPM conbinations... you will get increased MPG in 6th. But there are combinations of MPH/RPM where 6th gear will lose it's MPG advantage.

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Low RPM and Wide throttle opening is what I was taught to achieve the best mpg.

That being said, we like to get good gas mileage when we are on a trip. Getting high 20s is damn good for a high horsepower car like the 'Vette.

But WHY are we worrying about this with our 'Vettes??

I heard Civics get great gas mileage...

F

 

But WHY are we worrying about this with our 'Vettes??

Because It's the day after Christmas and we're bored and need something to pick on.

 

I believe on LS1tech I read a post that said the best rpm for gas mileage was 1700-1750rpm(on a mostly stock LS1), or about
72mph in a Camaro/Firebird. They based that on how much vaccum
the engine pulled, and it pulled the most vaccum at 1700-1750rpm. They use to sell mpg gauges, which just measured vaccum. When
you were at peak vaccum you were in the most efficient rpm range
for the engine, which returned the best miles per gallon.

 

he's right.

my point was only that in my scenario I've been able to achieve better gas mileage in 6th at 47 only because i live in a very very flat part of the country.

 

Gas mileage, was one of the reasons I went with a 6 speed, 2004, instead of an automatic. At 45 mph, is when I am in 6th. I like the over 20 mpg around town, and over 30mpg on the road.