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Thread: Any way to objectively choose engine?

  1. #1
    Hello All,

    I was wondering if any of you guys could point me in the direction of doing some preliminary calculations so that our team can objectively determine the engine we should go with. The current debate is between the 600 4 cylinder and 450 single cylinders.

    A part of our team is convinced we could tune the 600 to run optimally out of corners and the other part thinks the 450 dirt bike engines have superior torque curves with lower overall weight which will dominate.

    I'm trying to find an objective way to present the options to the team. I looked at some info and found tractive force but not knowing how the final drives will be tuned, I dont think we can use this.

    Any tips?


    in b4 this horse has been beaten to death

  2. #2
    Does your team have clearly defined goals? Does one engine type or another better suit the accomplishment of those goals?

    The components make the car, and compromises rarely make winners.
    "Good judgement comes from experience. Experience comes from bad judgement."

  3. #3
    What do you mean? Our goal is to come out of corners faster, reduce overall car weight and maintain similar power under low speed cornering.

  4. #4
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    I think you just answered your question then. I'd say one engine is definitely better than the other based on those goals.

    Which then brings us back to the bigger issue: are your goals the "right" ones?

  5. #5
    Which then brings us back to the bigger issue: are your goals the "right" ones?
    I feel like we're all having a philosophical debate about this here

    As an engineer, I want to develop some calculations to show objectively why one is better than the other?

  6. #6
    Yeah, I'm with Hector, sounds like you have answered your own question. Personally only a very small amount of the "engineering" I do involves actual calculations. I think that's the biggest myth of engineering education, is the "equation treasure hunt" that will always give you a "right" answer.

    Beyond that, it is actually quite a philosophical debate, in which so many factors are present that it's probably safe to say there isn't a "right" answer. That much could also be determined by the lack of either choice to consistently dominate at competition.
    Dr. Adam Witthauer
    Iowa State University 2002-2013 alum

    Mad Scientist, Gonzo Racewerks Unincorporated, Intl.

  7. #7
    A low to medium fidelity lap time simulator can be a good tool to objectively evaluate as many options as you like. It's also a good way to defend your decisions during the design judging event.

  8. #8
    Isn't this what a decision matrix is for?
    San Jose State University

    FSAE Chassis and Ergonomics Lead '12-'13
    FSAE Chief Engineer '11-'12
    FSAE Chassis Technical Lead '10-'11
    Formula Hybrid Chassis Grunt '09-'10

    "A designer knows he has achieved perfection not when there is nothing le

  9. #9
    Originally posted by Hector:
    I think you just answered your question then. I'd say one engine is definitely better than the other based on those goals.

    Which then brings us back to the bigger issue: are your goals the "right" ones?
    A low to medium fidelity lap time simulator can be a good tool to objectively evaluate as many options as you like. It's also a good way to defend your decisions during the design judging event.
    I'd listen to these guys.

    You may not have the time to develop a lap-sim tool for this purpose. If that is the case, I would suggest breaking things down into measures of success (in this case, competition points) and looking at the parameters involved and the sensitivities by which your "success" is related to those parameters. Given your current list of goals, however, I would have to agree with Hector.

  10. #10
    After further consideration I take some of what I said back. If your ultimate goal is track performance, a good lap sim would be a good predictor, and no doubt there are some calculations involved. For these large-scale type problems, I could also see other simulations like Monte Carlo simulations being used, with the right application of creativity. And barring that, as Robby pointed out, at least a simple decision matrix.

    But in truth, your spectrum varies between a scale lap sim (which may require lots of time to produce accurate results) to a decision matrix, which, let's face it, really is little more than attaching a number to some hand-wavy "philosophical" guesses. But if you really want to quantify something, especially when coming to a group consensus, it's not a bad method.

    Now with that in mind, and considering the resources most FSAE teams have, I feel that this well-used Patton quote is again appropriate:

    "A good plan, violently executed now, is better than a perfect plan next week."
    -General George S. Patton, Jr.
    Dr. Adam Witthauer
    Iowa State University 2002-2013 alum

    Mad Scientist, Gonzo Racewerks Unincorporated, Intl.

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