Thread: gas engine efficiency View Single Post
doclees
EcoModding Apprentice

Join Date: Dec 2012
Location: harrisburg pa
Posts: 121
Thanks: 5
Thanked 10 Times in 7 Posts
Quote:
 Originally Posted by some_other_dave Actually, the max BSFC typically seems to fall below the peak torque RPM. It seems to be somewhere around 2500 RPM in most cases for gasoline engines, while peak torque RPM varies a lot from engine to engine--in many cases, though, it is over 3000 RPM. -soD
Yes I got this thanks.

Quote:
 Originally Posted by some_other_dave The question of what speed to drive is not really the same question as what the most efficient RPM is, though. When you move a car, you have to use power to overcome friction, air resistance, rolling resistance, to warm up the engine parts, and so on. At anything over in-town speeds (guessing, 40 MPH?) the largest factor is air resistance, which goes up by the square or cube of the speed, depending on what kind of drag you're talking about. -soD
Got this too. I have a Jeep. boy to I got this.

Quote:
 Originally Posted by some_other_dave So the slower you can go, the less power needed to push your car through the air. But if you don't need to make much power, you have to throttle the air going into the engine way way down. And that isn't so efficient. So there's a trade-off. But the trade-off seems to generally be weighted so that lower speed is more important than the throttling losses, so for steady-state cruising the most efficient speed is typically "in top gear as slow as you can stand". For me, that is anywhere from 50 to 65 MPH, depending on a lot of factors. -soD
I'm trying to look at this mileage thing from inside out. I have no doubt that overcoming drag, especially air in my case, is the largest part of work performed. I would then assume that if an engine had a flat torque line instead of a torque curve I would want to gear it to put my most frequent driving speed at the lowest rpm that hits that near peak/peak torque?
So, in theory, must bolt-on's that improve near peak/peak torque improve BSFC?
I know I am missing pieces of this hence the questions.