Interpreting Engine Powertrain Performance Graphs & Hypermiling

Discussion in 'Fuel Economy' started by pressingonalways, Aug 18, 2014.

  1. I was rummaging the internet the other day and happen to come upon tested powertrain performance charts here:

    Assuming that you're accelerating onto a highway or something (don't have to worry about stopping after you start), you want to accelerate using the most efficient torque for your engine as well as being on the highest gear possible for the speed to maximize fuel efficiency during acceleration, is this correct?

    So for my car (, would it be accurate to say I want to be accelerating somewhere around 2500 rpm or so to capture the most efficient torque?

    It would seem that I definitely shouldn't be trying to accelerate any faster than that because there wouldn't be much more torque from between the 2500 and the 4500 rpm peak torque?

    For application, this would apply towards pulse and glides and accelerating from stop, right?

    I think the website could be a good resource to those wanting to know where the optimal rpm for their engine is for accelerating.
  2. some_other_dave

    some_other_dave Well-Known Member

    These graphs are of very marginal use to us, because they are all generated with the engine at wide-open throttle (WOT). If you are ever at WOT as a hypermiler, you are Doing It Wrong (TM).

    In general, stick with 70%-80% load, and right around 2000 RPM.

  3. ksstathead

    ksstathead Moderator

    What Dave said. Especially with your AT. You gain more by inducing earlier shifts at low rpm/high load.
  4. RedylC94

    RedylC94 Well-Known Member

    Yes, what someotherdave said is correct. You probably want to stay under about 2500 RPM while accelerating.

    "Most efficient torque" has no clear meaning. Every engine has an optimum combination of speed and torque at which it converts chemical (fuel) energy into mechanical power most efficiently. You want to stay close to that combination, to the extent practical without wasting power making the engine perform unneeded work. Engine performance can be graphed in ways that show efficiency at every speed-load combination, but that information is not shown on the WOT-performance plot you linked. If you can find a graph for your engine that shows part-load thermal efficiency or BSFC (essentially its inverse, aside from necessary constants), that would be more helpful.

    Thanks for the link to that interesting site. For what it is, it appears very competent, if a bit Eurocentric. At least that's my initial impression.
  5. Thanks for all your replies... guess it's back to being that guy that everyone honks at and drives around at red lights... :rolleyes:
  6. The Doctor

    The Doctor Old Dude, New Car

    One thing I never hear, is someone honking at me to get out of the way.
    It's usually the other way around! :stickshift:

    All those rpm numbers, etc., are useless, when you're going up a short entrance ramp onto an Interstate Highway that's loaded with 60,000# trucks, rolling at 80 mph.

    You either get up to highway speed while you're still on the ramp, or run the risk of getting creamed! Or, you're parked at the top of the ramp, waiting for a big hole in traffic that you might be able to jump into. Again, you'll want all the acceleration you can get in the least amount of time.

    If no-one is in my way, when I'm getting on the BIG Road, it's "Pedal to the Metal" till I'm firmly positioned where I want to be in traffic.

    A few days back, I had a clear I-75 entrance ramp ahead of me and I joined the first lane of three at 80 MPH and my little 1.6 was screaming like a banshee. By the time I could get over into the High Speed lane, Gertrude (my Kia Soul) was howling like a long tailed cat in a room full of rocking chairs and my SG was showing 90 mph. I had to tap the break to keep from running over a Benz that was only doing 85.

    Great performance comes at a cost....usually in gasoline burned. But, I'd rather burn some extra gas, than get run over by an 18 wheeler.

    I was so impressed by the performance of my little Kia Soul, when I first got her, I wanted to know just how much horsepower she was capable of.
    So I took her to a local Speed Shop and had her Dyno Tested.


    The professional Dyno Operators were amazed at how fast that little 1.6L engine torqued up and how much horsepower she put to the wheels. The best of two pulls was 111.1 BHP where the rubber meets the road.

    When under full acceleration, my six speed AT, will shift at just over 6000 rpm.
    The computer knows where the end of the power band is, even when I don't.

    Cheers Mates, and Happy Holidays!

    The Doctor :cool:
  7. The Doctor

    The Doctor Old Dude, New Car

    Hypermiling is for the highway, not at a stop light!

    Put the hammer DOWN! and don't be the guy getting honked at. Eh?

    Happy Holidays!

    The Doctor :cool:
  8. some_other_dave

    some_other_dave Well-Known Member

    I use 70-80% load, and cannot remember the last time I got honked at for not accelerating fast enough. And it's been weeks since an 18-wheeler ran over me and squashed me flat... ;)

    There's no need to go "pedal to the metal" in everyday driving. If you like to do it, that's up to you--but realize that you're doing it for fun, not for survival.

    Oh, and if there's nobody in front of me on an on-ramp, I will go over 80% to some extent. Generally until I can get the tires singing--figure 50-60 on the ramp. I do it because I enjoy it, not because I think I have to in order to survive. (If anything, it reduces my odds by reducing the margin of error I have if anything goes wrong.)

  9. brick

    brick Answers to "that guy."

    Any MA residents want to vouch to the horrors of Route 2 anywhere east of Leominster? Talk about're sitting at a stop sign (IIRC?) 100ft from "55mph" traffic going 70+ and looking for a 2 car-length gap to occupy if you hit it at the wrong time of day. That's the only place I have ever experienced a true need to hit an on-ramp at WOT and full-clench. Everywhere else I get up to speed at moderate load, look over my left shoulder as many times as it takes, and slide into traffic. That worked just fine in the 5.5 years I had my Prius and it works in my [so far totally unnecessarily] much quicker current ride.

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