Torque and Acceleration
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  1. #1
    2000+ Brad's Avatar
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    Torque and Acceleration

    Many a discussion has been had in this forum regarding the finer details of power, torque and acceleration, however a question still remains;

    Where is peak acceleration found in the rev range of an engine?

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    If torque is the twisting force of an engine, the more torque there is, the more ability there is to overcome resistance ie. Wind drag, inertia, and wheel resistance.

    Therefore it follows that the maximum acceleration of a car should be at the revís which provide the most torque (ie. Greatest ability to overcome drag), which in most French cars is comparatively low. I know my S16ís peak torque is around 3600rpm, however I would never of picked this to be the peak acceleration point, more like 5,000rpm

    Arguments based on peak power are irrelevant because power is only a function of torque AND revs. Torque drops off past its peak, however the power keeps climbing because the increase in revs allows more power to be made, however this stops once torque drops off too quickly for the revs to gain back.

    Perhaps someone with a g-tech can confirm this for me.
    B to the R to the A from the D
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  2. #2
    1000+ Posts dino's Avatar
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    what u r saying makes sense...2 me (using the 205 as an example)...peak acceleration seems 2 occur around peak torque...everything above that seems more like squeezing blood out of a rock...it would be really interesting to compare quarter mile figures where one car is driven according to max torque and the other to max kw/rpm...i m definitely not claiming to be an expert in this field but i would think that many of us like to wring out every kw out of our cars sometimes just because of sheer enjoyment of being able to freely redline or in my case just because i m desperate as those parked cars are aproaching me way 2 fast .. i think of max acceleration in reference to how hard my back is pushing into the chair not how white my knuckles are turning...so yes i obviously dont have a g tech...another thing is that gearing obviously needs to be right and thats also the reason why we STRETCH the revs out sometimes..to componsate on the loss...some of us enjoy this stretching more than others obviously...

    cheers
    dino

  3. #3
    Fellow Frogger! AlsPug504's Avatar
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    It is of interest to me. My mate has found with a medium size turbo the torque was very high. He was running 8psi. And beats guys with large turbos that only boost in statospheric revs. yet there power is twice his. I guess this is the subject of drivablity.

    Al

  4. #4
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    Interesting topic given I've owned cars with two completely opposite characteristics here.

    I definately notice a difference in where the best acceleration is when I changed over from the 306XR (XU7JP 1.8L 8v engine) to the 306XSi (XU10J4R 2L 16v engine).

    The XR's peak torque was at 3000rpm and peak power was at 6000rpm but revving it that high was always pointless.

    The XSi's peak torque is at 4200rpm and peak power at 5500rpm, so it's better to keep the revs higher.

    Having said that, the 16v engine is much happier to rev so I guess it likes it? On the issue of driveability, this engine is happier to lug away from a *just* rolling start in second for example, than the 1.8 engine was. My only problem is if I get in the C3 and try that I stall it

    Derek.

  5. #5
    Fellow Frogger! MYT205's Avatar
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    Another important factor is that you need to look at what revs the car "falls back to" once you have changed gears at the max torque revs. This may land you in an area that is substantially lower than max torque, whereas reving past peak torque rpm may land you "back" at peak torque once you have changed gears.

    Thats a problem with the VTEC engines. You MUST keep the revs up in the VTEC band otherwise torque falls way horrifically.

    Darren

    PS. Brad. Do you mind if I rip this topic off for discussion on another forum, namely PF? I'd be interested in their thoughts as well.

    Cheers

    <small>[ 16 April 2003, 05:57 PM: Message edited by: YEL020 ]</small>

  6. #6
    2000+ Brad's Avatar
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    Sure, send me the link when you have so I can keep an eye on it.
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  7. #7
    1000+ Posts dino's Avatar
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    in regards to vtec...u r absolutely right there....BUT there is still so many guys that insist having the SHIFT lights (tacho mounted)in their riced hondas...kind of irrelevant when u think about it (as the vtec cars need to be screaming their heads of most of the time to get the type of performance they r capable of)...but they r great on high torque v8s and the like that do not necesarilly deliever best acceleration once u go 2 far past peak torque...

    cheers
    dino

  8. #8
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    It's at max power main and simple.
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  9. #9
    Guru davemcbean's Avatar
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    The Pupat:
    It's at max power main and simple.
    WRONG!

    Obviously you're not an engineer.

    Acceleration = force/mass

    So the maximum acceleration peak occurs when the force at the wheels is greatest, which happens to be at peak torque in first gear. That's why the wheels break traction so easily at that point.

    To acheive maximum overall acceleration you have to rev it quite a bit past peak torque and sometimes even past the power peak, so that when you change gears it falls back onto the torque peak, as has been stated before. Just when you change gears depends on how close the gears are and the overall torque curve.

    Dave

    <small>[ 17 April 2003, 07:11 AM: Message edited by: davemcbean ]</small>
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  10. #10
    2000+ Brad's Avatar
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    davemcbean:
    To acheive maximum overall acceleration you have to rev it quite a bit past peak torque and sometimes even past the power peak, so that when you change gears it falls back onto the torque peak, as has been stated before. Just when you change gears depends on how close the gears are and the overall torque curve.

    Dave
    My original question only really related to acceleration in one gear only and didnt bring into the equation gears and when to change as this complicates things a tad more, however very valid point.
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  11. #11
    Fellow Frogger! MYT205's Avatar
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    Here is the link to a discussion on the same topic on another forum.

    <a href="http://board.performanceforums.com/forums/showthread.php?s=&postid=537761#post537761" target="_blank">http://board.performanceforums.com/forums/showthread.php?s=&postid=537761#post537761</a>

  12. #12
    1000+ Posts brenno's Avatar
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    Teehee, the Poops got owned =)

  13. #13
    1000+ Posts PeterT's Avatar
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    Good discussion boys. As Dave said, F=ma, so the perfect engine would have a flat torque curve, like an electric motor or to a lesser degree, a turbo charged diesel. Of course as you get faster, you need power (kW) to overcome wind resistance.

    '92 205 Mi16
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  14. #14
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    Dave: Funnily enough I sort of am. Final year mechatronics engineering student. So I'm going to blame it on the fact that the focus is mainly on the controlling systems.

    Ohh and I did work out later that it's at peak torque in a specific gear, though that's not true if you got a CVT gearbox.

    Yeah yeah shut up Brenno :p

    <small>[ 17 April 2003, 05:41 PM: Message edited by: The Pupat ]</small>
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  15. #15
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    PeterT:
    Good discussion boys. As Dave said, F=ma, so the perfect engine would have a flat torque curve, like an electric motor or to a lesser degree, a turbo charged diesel.
    This should fit your bill - and it's not a diesel either.

    <img src="http://users.bigpond.net.au/skystar/B5244T3.jpg" alt=" - " />

    The torque curve is flatter than the Nullabor

    Of the diesel's I've seen, whilst they have great torque at low revs, they don't seem to have as flat a torque curve as the low pressure turbo petrol engines - the torque doesn't last if you push hard.

    Regards,

    Justin

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  16. #16
    1000+ Posts Warwick's Avatar
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    I think POWER = TORQUE times REVS
    "Now my dream lies shattered like the shards of a broken dream"

  17. #17
    Guru davemcbean's Avatar
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    The Pupat:
    Dave: Funnily enough I sort of am. Final year mechatronics engineering student.
    What a coincidence. I'm studying mechatronics at UNSW. I previously did mechanical engineering at TAFE and Port Kembla steelworks.

    Dave
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  18. #18
    Fellow Frogger! AlsPug504's Avatar
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    I think POWER = TORQUE times REVS.

    Yep you forgot the constant thow. 5252 for Hp so

    RPM x TORQUE
    5252 = HP

    <small>[ 20 April 2003, 02:49 PM: Message edited by: AlsPug504 ]</small>

  19. #19
    Fellow Frogger! Ralph's Avatar
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    Hi all,

    <a href="http://www.physics.uoguelph.ca/tutorials/tutorials.html" target="_blank">http://www.physics.uoguelph.ca/tutorials/tutorials.html</a>

    Cheers,

    Ralph.
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  20. #20
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    Well ive got a degree of Applied Science in Mechanical Engineering and Business... dance

    Who cares who has what; i know a final year Mechanical Engineering student who dosent know too much at all about cars...

    My advice on the matter is to get a dyno sheet printed. Select several points on the dyno curve. Once you have these points, add the readings together then divide by the number of samples. This will give you an indication of the average power your engine develops across these points.

    When you modify something on the car, repeat the process and then you can compare graphs and see wether your modification has produced a better average power.

    You can also test your rpm drop in each gear with a dyno run to develop an ideal shift point.

    AlsPug504:
    It is of interest to me. My mate has found with a medium size turbo the torque was very high. He was running 8psi. And beats guys with large turbos that only boost in statospheric revs. yet there power is twice his. I guess this is the subject of drivablity.

    Al
    Obviously those guys with 'large' turbo's dont know what they're doin. Thats the motto i guess; usable power. For example, why would you put a huge turbo in an old car that redlines at 5000rpm that spools up when your approaching your redline ?

  21. #21
    1000+ Posts CHRI'S16's Avatar
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    brad, in your original post you wanted to compare times with either peak tourqe shift points or peak power shift points? is that right..
    well i sort of did this except i used a GT-MR2 and a G-tech (Old style) about a year ago... we had a Dyno sheet to look at shift points (for both Nm and Kw) and we set the fully SICK bro Monster tacho shift light accordingly on each run, we performed this test in a, ahem, closed road. but we wern't sure what happened as actually changin when the tacho goes ON, is harder than seems at first...
    I cant remember exact figures but the Nm(tourqe) 0-100 was pretty close to 1.5 times of the peak power, and was pretty close to that 1.5 for the full 1/4 mile.... funny it wasn't that quick and i think i remember it ran constant high 13's... so about 19's would be my guess for the Tourqe times.
    How on earth did you think of that idea, wayto brain storm, i have to borrow my G-tech back from our mate and compare again.... and in my car too. Controlling the wheelspin depended on how you took off on the MR2.
    cheers Xq
    ... ptui!

  22. #22
    2000+ Brad's Avatar
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    XQ, my original post was only possing a basic question as to where on the rev band you would have the greatest acceleration, not to find out how to get the best 0-100 etc time. This has too much to do with gearing and revs to have a basic discussion.

    Take a look at <a href="http://board.performanceforums.com/forums/showthread.php?s=&postid=537761#post537761" target="_blank">this</a> PF thread for more talk of it.
    B to the R to the A from the D
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