Someone told me once you use 20% more fuel at 80mph v 55mph, but you are going 25mph faster with is more than 20% faster.

I don't know if that was taken into account or not, if that every second you use 20% more, or 20% in the same distance traveled.

 

Here's a better explanation: They're wrong.

All it takes is one tank of Summer fuel at high speeds vs. a tankful of Winter fuel at lower speeds for people to mistakenly come to the conclusion that they always get better mpg at higher speeds. But it just ain't true.

I will bet a bottle of Don Julio that in a controlled experiment, an S2000 will get much better mpg at 60mph vs. 75mph.

 

Interesting discussion there. Lets add a new wrinkle.

So lets take the 2010 Fisker hybrid Sedan example and see high rpm or low rpm is best for mpg.

If you do not know, the Fisker hybrid is an EV with a gas engine to produce power (plugin capable). No drive train between the ICE and the wheels of the car.

Lets say the engine is designed to most efficiently product electricity for the car to move its EV motors (and store in batteries if surplus juice is still unused). Would maximum HP and/or TQ be best at high rpm, or lugging the ICE around at low rpm to produce most energy?

 

For the Fisker case horsepower is less relevant than watts or kilowatts. 1 kilowatt is 1.34 horsepower IIRC. There are many ways to go about using the internal combustion engine as a generator to recharge a battery pack for an electric motor. This was actually where I thought Honda messed up with its hybrids, because they make great generators. I believe it takes 25kw (33.5 hp) for the average car to cruise at 50 mph, this is an unverified number but I think it is close. This will obviously draw the batteries down. You could idle the gas motor with light load all the way down to where you need more power than the batteries have in storage, and you would have to speed up the gas motor to make more power to make up the deficit. Or you could leave the generator off until the batteries don't have the juice and you have to run the gas motor to charge the batteries and operate the car. Either way you are going to have to speed up the gas motor with a heavier load to charge the batteries AND provide a power surplus to operate the car as well.

Generators usually idle or spin just fast enough to cover the current load, having a battery pack as a storage device just gives you more options on how to run the generator. So in true Yogi Berra fashion the answer to your question is yes.

Edited from here down...
My personal opinion the most fuel efficient way to recharge the batteries from dead to full would be to run the gas motor at maximum output for the shortest amount of time and then shut it off. This won't be best for the batteries because they prefer slow draw and slow charge for maximum life but I think it would be the most fuel efficient.

 

oy.

why do people enjoy going fast in a straight line anyways? the difference in time is literally in minutes.

 

i often hear the 'minutes add up' argument, but i just like to drive fast for its own sake. its fun.

 

i used to drive fast in a straight line, but ended up feeling like a hamster on a treadmill for some reason.

 

Forgetting to upshift when at 65 mph?

 

you're right.

i drove through Oregon with posted speed limits on I-5 of 55mph-60mph and got 35mpg. I stuck close to that limit as i've heard the state patrol is notorious for giving out speeding tix and setting up speed traps. it helps that the state is very flat for most of that driving. i put it on cruse and let her go.

through cali, i sped up to 75mph and got 26mpg. still respectable but not nearly as good as through OR. the drive thru OR was mind numbingly boring and seemed to take forever though.