does higher HP = higher top speed?

Discussion in 'The Safe Zone' started by B.mad, Nov 13, 2014.

  1. B.mad

    B.mad Well-Known Member Preferred Vendor

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    Obviously there is many factors to take into consideration like wind speed, resistance, aero, gear ratios etc etc

    but just say hypothetically speaking you have X car with X resistance, X speed wind, X aero etc etc, with X amount of power. it goes X top speed

    now you decided you want your top speed to be faster. So you build X car to have Y amount of horsepower. Now you put it in the same exact conditions as before and all parameters are exactly the same except for the amount of power. Does your top speed still stay at X just gets their faster? or is your top speed now y?

    to me it seems like horsepower and torque only decrease the time it take to reach top speed and not actually increase the top speed. anyone care to explain?
     
  2. wmfateam

    wmfateam Active Member

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    If the gear ratio and max engine rpm remain the same, and you are not limited by distance, yes top speed will remain the same.
     
  3. Orange 94

    Orange 94 Moderator Staff SN95 Supporter

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    There are so many factors to this. The transfer of power is likely a limiting factor.

    In the case you describe though, theoretically more power = higher top speed.

    HP is a measurement of power. Power is work/time. Work being in this case the force x distance. So HP is force to move a distance with respect to time.

    To keep a constant speed the car must apply a force equal to the forces working against the car. Mainly air resistance, but also friction on tires and parts.

    The higher the speed, the air resistance gets much larger. To increase your speed you must over come the force.

    You do need a certain amount of power to achieve a certain speed.

    This explains it better.
    http://phors.locost7.info/phors06.htm

    I'm not sure if you can definitely say more power = higher speed in the same setup. I'll have to look more into it.
     
  4. B.mad

    B.mad Well-Known Member Preferred Vendor

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    gotcha. Its just a question that plagued me. Because similar powered cars have different top speeds. not taking into consideration the gear ratios.

    example a ferrari 458 has a similar top speed as a 2014 shelby gt 500. Its a 550 HP car vs a 662 hp car. and they have similar final gear. with the 458 being 0.69 with a differential gear of 5.14 and the shelby final gear of .63 and a differential gear of 3.73.
     
  5. Orange 94

    Orange 94 Moderator Staff SN95 Supporter

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    That's comparing two totally different cars. They are in no way similar.

    Power doesn't directly translate to speed. If you compare the exact same vehicles, theoretically the one with more power will have a higher top speed (if it has enough gear/rpm to do so). I think powertrain would still make the biggest difference. I don't think manufactures would design a car to have left over gear at its top speed, they'd dial that back to get better acceleration.
     
  6. B.mad

    B.mad Well-Known Member Preferred Vendor

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    ok just so i have a grip of what you mean. so a manufacture wouldnt have a top speed of say 160 mph at about 4000 rpm. it would be 160 mph at redline which approximate 7000 rpm.
     
  7. Orange 94

    Orange 94 Moderator Staff SN95 Supporter

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    Yes.

    Basically if you're going to improve top speed you need to play with gears and power. Aerodynamic mods would also greatly help.

    With a straight oem car that has a top speed in the final gear at redline won't have a higher top speed with more power. It will just get there faster.
    If an oem car has its top speed half way to redline (unlikely), then adding more power should in theory increase speed.

    This is assuming no electronic and other factors controlling top speed.

    I should also mention it depends how your hp peaks. Say if your hp peaks at 4500, then that is where your top speed will be at. If the hp drops at 6000 then it shouldnt be able to make it there in theory.

    That's my understanding anyways.
     
  8. ttocs

    ttocs Legend

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    what if you were going down hill with a tail wind and had all your girls fat-friends in the car?
     
  9. Orange 94

    Orange 94 Moderator Staff SN95 Supporter

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    The g-force would cause you to black out. You might travel back in time also.
     
  10. kb1982

    kb1982 Active Member

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    With more power, you would be able to push through higher amounts of areodynamic drag, allowing you to go faster. In the land speed game, frontal area makes all the difference in the world due to areodynamic drag coefficients.
     
  11. torch318

    torch318 Active Member

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    Tire size also plays a role in top speed not just gear ratios a larger tire with the same gear ratio is going to travel farther with each rotation.
     
  12. B.mad

    B.mad Well-Known Member Preferred Vendor

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    ahhh that totalllly makes sense now. Going up I always thought higher HP means higher top speed, but i stopped and thought bout it recently, how does that make sense? and considering when using tools like tremecs gear calculator, it cant be right for every car if they have different HP numbers.





    and our cars suck at that LOL.


    oh ya im away of that. tire size changes the gear ratio theoretically speaking.
     
  13. 96gt4.6

    96gt4.6 Member

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    really just depends on what runs out of breath first

    too much gear= hp will limit top speed
    not enough gear= gears will limit top speed
     
  14. OnyxCobra

    OnyxCobra Legend

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    assuming the car isn't limited by it's gearing then more power will make it go faster. basically at that point you're having to increase the power to overcome wind resistance. If your top speed is limited by gearing then more power will just get you there faster, the top speed will not change.
     
  15. B.mad

    B.mad Well-Known Member Preferred Vendor

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    According to tremec's calculator, with 2.73 and a 315/35/17 tire and .68 OD at 6000 RPM, ill be going 246 MPH.

    i doubt that is possible LOL.

    other question. How does the speedo work? is it just geared? so technically speaking it doesnt take into consideration wind resistance? because if you have, say 50 MPH winds, i doubt youll go the same speed as if it were 20MPH. so the geared speedo's arent accurate?
     
  16. D3VST8R96GT

    D3VST8R96GT Well-Known Member

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    Those are mechanical calculations.... adding in the drag coefficient makes shit intense!!!!
     
  17. Orange 94

    Orange 94 Moderator Staff SN95 Supporter

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    Speedo is gear driven from tranny. The speed is the rotation of your tires. Wind doesn't matter, just makes the engine work harder.

    As for the actual accuracy, its meh.
     
  18. seijirou

    seijirou New Member

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    Horsepower governs all of it. Both your top speed, and how quickly you get there.

    That assumes you don't run hit a rev limiter. 7,000 RPM in 5th gear is the same MPH, regardless of how much horsepower is behind it. If you can reach that with 500 horsepower, 1,000 horsepower will be the same speed. If you're hitting a rev-limited 7,000 RPM and you don't have a 6th gear to shift to, then both will get to your top speed, but the 1,000 HP will get there faster. If you add a 6th gear, 7th, and so on, eventually the 500 HP will hit a terminal velocity where the resistance meets the power and you can't get more speed. The 1,000 HP will continue accelerating to some higher terminal velocity.
     
  19. ttocs

    ttocs Legend

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    how did you know I have been waiting over 2 yrs for this answer?
     
  20. Addermk2

    Addermk2 Well-Known Member

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    im pretty sure this thread gave me cancer...