RPM-MPH chart for W58 & stock wheels/tires - Page 3

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  1. #21
    CelicaSupra.com Member Ross's Avatar
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    StanS, I wasn't really trying to argue with you.
    I've always agreed with your formulas, I've just never heard this one before. You admit it may be a little more than what the formula suggests.

    I'm trying to understand this - I thought that if you were trying to push a car shaped like a brick through the air it would take more hp than a more streamlined one. This is cd isn't it?

    But if you have any downforce, the faster you go, the harder it pushes you to the road, therefore requiring more hp.

    So don't we have air resistance and rolling resistance?

    Or is air the only important resistance, which is why engineers have wind tunnels?

    And also, I think I read somewhere, that without gearing multiplication ie. 4th gear (1:1) or 5th (overdrive) you can't get any more revs than where your peak hp is developed. So if peak hp is developed at 6100rpm, you couldn't do 6500rpm in 4th or 5th.
    Is this correct?
    I'm too lazy to type long replies.

    Ross from Oz

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  3. #22
    CelicaSupra.com Member CarFreek's Avatar
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    When car and Driver did top speed test a few years ago with tuner cars, they had a neat little horsepower formula from top speed and tire size gear ratio-basically, if you arent driving a brick, 400 hp=160mph-500=175-600=185 and you need 750 to do 200-Callaway sledgehammer had 880 or so and did 217 mph with slippery vette body-I would love to do Bonneville some day in any car-what a rush-back in the day, everybody had real problems crackin 200 at Bonneville-Air resistance/lift becomes a reaL BIG FACTOR at about 175
    86 SDR-"Shuttlecraft" 16" Drag dr-27 wheels, Coilover/AGX/Celica Arms front, Camber Mod/Cut Springs rear, Poly Bushings all around, Whiteline sway bars, 13" bbk front, and 12" bbk rear, Weir Diff bushing, Pacesetter with custom RABID CHIMP mandrel bent 2.5 with Flowmaster resonator, short shifter, 5m-GZE using upgraded sc-14 Toyota supercharger, with Custom RABID CHIMP piping..

  4. #23
    CelicaSupra.com Member
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    didn't take it as arguing or flaming. just trying to reply with info. medium distorts intent as we're aware.
    I'm trying to understand this - I thought that if you were trying to push a car shaped like a brick through the air it would take more hp than a more streamlined one. This is cd isn't it?
    yes

    But if you have any downforce, the faster you go, the harder it pushes you to the road, therefore requiring more hp.
    reaching the limits of my knowledge here but up/downforce is produced by the pressure pushing down on car top minus pressure pushing up on car bottom. since air path over car top is longer the air "moves" faster over car top and due to Venturi effect pressure on car top is lower than on car bottom resulting in more lift at hi speed. think that cd takes this into account.

    So don't we have air resistance and rolling resistance?
    yes, as i said formula only takes aero into account, but i believe that aero is by far the most dominant effect.

    And also, I think I read somewhere, that without gearing multiplication ie. 4th gear (1:1) or 5th (overdrive) you can't get any more revs than where your peak hp is developed. So if peak hp is developed at 6100rpm, you couldn't do 6500rpm in 4th or 5th.
    Is this correct?
    Yes. Remember that Power = Torque x [Speed (or RPM in a gear)]. Torque (to ground) is what pushes car, not hp. At gear ratio of 1:1 (or higher) and peak hp, T must be falling with increasing speed (RPM) , by definition, since constant T with increaing RPM would yield increasing hp and we said we just passed peak hp. As RPM and speed go up, aero drag requires more T to push the car, but T is falling with increasing RPM past peak hp.
    hope this makes sense.

    Sorry, i didn't respond earlier but i lost topic notification.

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  6. #24
    CelicaSupra.com Member Ross's Avatar
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    OK It's making sense now.
    Your maximum speed would be at the RPM that you're creating maximum torque. For a 7M-GTE that would be 3200 RPM, no just re-read you post again, it's where hp starts falling off, so for the above 7M-GTE that's 5600 rpm


    Thanks StanS
    I'm too lazy to type long replies.

    Ross from Oz

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  7. #25
    Administrator Tommy's Avatar
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    Don't forget that OD reduces torque to the rear wheels by at least the percentage of ratio. Ie. .78 OD will reduce RWTQ by 22%. 300 crank hp turns into 234 whp. Add in drivetrain losses and the TQ #s fall really fast in OD.
    I hth.
    Jamie

  8. #26
    CelicaSupra.com Member Ross's Avatar
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    Thanks Jamie
    I was really just thinking about 4th at the moment, trying to decide what difference (if any) there would be changing from a 3.9 diff to a 3.7
    I know it would give lower revs per mph, but would you also go faster?
    I'm too lazy to type long replies.

    Ross from Oz

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  9. #27
    CelicaSupra.com Member Dean's Avatar
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    Quote Originally Posted by Ross
    OK It's making sense now.
    Your maximum speed would be at the RPM that you're creating maximum torque. For a 7M-GTE that would be 3200 RPM, no just re-read you post again, it's where hp starts falling off, so for the above 7M-GTE that's 5600 rpm


    Thanks StanS
    Ross, this is not necessarily true.
    In reality, max speed will be at the point where your engine power = drag + rolling resistance.

    Let's say that at 5600 rpm you are making max HP which just happens to be 700 HP. Let's say that at 6000 rpms it has fallen off to 600 HP. If 600 HP is sufficient to overcome drag and rolling resistance at that speed, then you will continue to accelerate past your engine's peak HP.

    I hope that example makes sense.
    Dean
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  10. #28
    CelicaSupra.com Member DON's Avatar
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    Quote Originally Posted by Tanyas Mk2
    would like to see someone pull 161mph out of a 3.73 mk2, that'd be nice...
    so far all I've heard was topping out at 125-135 in any particular mk2...
    mathmaticly it should be possible
    :?
    Agatha has surpased 150mph, with her 3.73 trutrac rear end. :twisted:
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  11. #29
    CelicaSupra.com Member Import_Eve's Avatar
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    Wow! This is pretty tight!
    Check out what I am selling... Hidden Content

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  12. #30
    CelicaSupra.com Member supra_mkii's Avatar
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    I have a 4.10 diff in my car. Have had her up to limiter in 5th gear. It showed 245km/h on the speedo. Had 225/60/14 on back then. Whould like to go back to my 3.73 though. Hard to find one in SA.
    85 supra 2JZ-GTE ....everything else is just transportation.

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