My stock 2001 in 5th gear at 47 mph turns 1500 Rpm's.....maintaining 47mph in sixth gear the rpm's are 1000.....a non-tecky like me would think that you would therefore get twice the mileage at 47mph in sixth or am I nuts.

 

Yes, you're nuts.

Actually at those low speeds you'd probably get better mileage in 5th than in 6th. 1000rpm isn't anywhere near the most efficient engine speed.

Larry

 

stop trying to get him to keep it in fifth.
next time pull up our instant fuel on your dic.

i've been able to achieve 39 mpg at 48 mph in 6th.

 

what was that...coasting down with no throttle?
Heck, I can get 99mpg to show...doesn't mean anything.
Take a 100mile trip in sixth at 48mph, then take the same trip at the same speed in fifth. I'd bet money the second trip would yield higher miles per gallon...
Peace.
Larry

 

I got 32mpg in 6th gear on a 160 mile trip with my 04 coupe. Speed was 65 mph most of the time. trip was 90% hiway driving and 10% city. I wasnt trying to get the best mileage, it just worked out that way.

 

even not accounting for engine fuel efficiency at any RPM range, you have to consider that eventhough you're running lower RPM's in 6th, you are running at a higher load.

 

This guy knows what he's talking about. You really want to be seeing closer to 1500rpm for best efficiency. I don't use 6th till 60mph with 3.90s.

Dope

 

yeh that, or crusing down the road for an extended period of time on a strech of road at 3 am when there is no cars and no stop lights.

you do what you want .. i'll trust my computer.

 

At 47 mph, you'll probably see very little difference in mileage when in 5th as opposed to 6th. To operate on a level road a car needs a certain amount of power to move at a fixed speed in 6th. The power is required to overcome internal friction, rolling resistance and wind resistance. Other than a slight increase in internal friction from the higher rev's, everything else is the same when in 5th. Increasing the speed will increase the difference proportionally.

 

problem is... you need more fuel to maintain the car @ 47mph in 6th - then you would in fifth. So there is no MPG gain.

 

Never thought about trying an experiment like this. However, I prefer to have a little acceleration capability at that low of speed. Doubt that you will get better mileage in 6th than 5th at that low mph.

 

so how about if you live in florida (which is all flat) and it's a calm night with no wind.

 

.....4th gear.

 

How's the saying go, max efficiency at the torque peak rpm, max accellaration at max hp rpm? In that case, you'd get the best gas efficiency if you could max your load with the car in any gear so long as it's at the rpm where your motor creates max torque. Unfortunately standard transmissions don't allow this concept to be realized. Continouosly variable transmissions are supposed to work off this concept. For cruising it'll rev for max torque, then continually adjust the gear ratio to keep it there. For accelleration, it'll rev to max hp and again continually adjust the gear ratio to stay there.

 

interesting scenerio. Usually people get too caught up in the "mathematics" and forget the real world isn't as predictable.

think of it as the amount of rear wheel thrust needed to maintain a specific speed. So you would need a "set amount" of AF mixture entering the engine to generate the correct thrust needed to maintain 47mph. 6th gear robs the drivetrain of thrust. In 5th gear, there are some instances where less AF mixture would be needed to generate the same amount of thrust (dependng on whether the engine was at or below it's efficient RPM powerband) then 6th gear.

It's not the RPM registering on the tachometer at a sppecific speed that determines MPG ... it's the amount of AR mixture needed to maintain that RPM. And at such low rpms seen driving 47mph in 6th.... the engine is so far below it's powerband that it takes an additional amount of extra AF mixture (due to the engines inefficiency) then it would at say 1800rpm.

The question becomes which gear "over the long run" would end up using the less amopunt of AF mixture. Once the engine RPM's are up enough to be in the power-band, I would think 6th would always be the most efficient.

but I'm sure (like you pointed out) there may be a unique scenerio that would always show the opposite.

 

So 1500 x 8 explosions per minute can use less gas than 1000 x 8 explosions per minute....my guess would be that rpms and gas usage would follow proportional lines on a graph. But then I could be fullaprunes.......how about an answer from a certified automotive engineer who would really know the real deal...

 

[QUOTE=lottavettes]So 1500 x 8 explosions per minute can use less gas than 1000 x 8 explosions per minute???....I wouldn't bet my vette on it ...my guess would be that rpms and gas usage would follow proportional lines on a graph. But then I could be fullaprunes.......how about an answer from a certified automotive engineer who would really know the real deal...

 

Those Numbers on the DIC are not accurate. Especially when your trying to measure the extemeties of the cars abilites. The Instantanious MPG is a calculation based on thd last 70 ignition cycles of the car, I think.

 

And to think I always thought the issue with the Corvette was 0-60 and the 1/4 mile, and PERMAGRIN!!!!!
Little did I know that a degree in Physics and Math would come in handy!!!!!

Would you people...please , oh please.....ENJOY THE CAR!!!!!!!

Gas mileage issues are for Hyundais and Hondas!!!!!!!!!


For those with NO sense of humor......Oh Well!!!!!!

 

Simple answer: yes.

Long answer: It depends on which fuel cell the computer thinks the engine belongs in, and that depends on the driving conditions to include: throttle position, intake air temp, coolant temp, and a couple other things I can't think of.

Of course engines have different efficiencies at different rpm's. If they didn't, the torque and hp power bands would be absolutely flat. The motor may actually use the same amount of fuel during each combustion cycle, but the effectiveness of each charge is dictated by many factors during design like intake runner length and diameter, throttle body size, fuel injector position, combustion chamber shape and volume, valve size and lift, exhaust configuration. After the design has been implemented into a production engine, the tuning can change the power curve even more, and after that it's all about what fuel cell the motor is in and the rpm's.

Efficiency matters a lot for us too. Yeah, sure a lot of us don't care so much for mpg's, but most of us would like our motors to use a lot of fuel efficiently so it can put out lots of power.

What do I know though, I'm not a certified automotive engineer. How 'bout I think there a lots of steriod enhanced hamsters under my hood that make my car go fast? I really think there is a sewing machine in there instead of a cam, lifters and rockers. Those exhaust sounds come from a piece of card board flapping against the wheel...still haven't figured out where the noises come from when the car isn't moving.