Help me understand, does weight play a HUGE role in top speed?

Discussion in 'The Garage' started by DaTT, Jun 8, 2012.

  1. DaTT

    DaTT Garage Moderator
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    A guy told me that his 2000lbs Honda Civic with 450 FWHP would do 180 Mph. I don't believe him. I figure aerodynamics would play a much larger role than weight in top speed.
     
  2. Doppel

    Doppel Lifer

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    It actually plays zero role in top speed, at least once you remove any impact on rolling resistance (which would increase as weight does). It's all about aerodynamics.

    I don't know the specific math of what it would take an S2k to hit 180 mph but if his car really has that much horsepower it's probably not far off.

    Stock car does about 149 according to a link I found with 237 horsepower, so doubling that I think 180 sounds pretty doable.
     
  3. jmarti445

    jmarti445 Senior member

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    Gear and Final Drive ratio, Engine RPMs, and Horsepower have a lot to do with top speed. Other things such as co-efficient of drag and surface area also affect top speed. Making a car lighter may have an effect if the Engine RPMs are able to overcome the weight difference but weight has more to do with quickness vs top speed.
     
  4. Demo24

    Demo24 Diamond Member

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    Its a civic, not an s2k.

    The limiting factor here is going to be aerodynamics, followed by gearing. All depends on if he put in longer ratios to even have the possibility of spinning the wheels to 180mph, which I kind of doubt. Most likely it probably does closer to 130, give or take some (I have no idea what a stock civic is geared to in 5th, pretty low from my experiences in Honda manuals so maybe more like 115).
     
  5. LTC8K6

    LTC8K6 Lifer

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    Back in the mid 80's, those Nascar cars were hitting 230 mph in testing at Talladega.

    Tim Richmond took a Nascar Monte Carlo to over 240mph at a top speed comparo with Al Holbert's Porsche 962LMP, which could only manage 228 on the same track.

    The main reason was that the Porsche had a lot of downforce, and the Monte Carlo had comparatively little. Aerodynamics.

    The Porsche only hit 212 initially, then managed 228 with a lot of downforce removed, but it still had more df than the Monte Carlo.

    Most people think the Nascar cars are "bricks", but in fact they really aren't. And they weren't, even back then.

    Had the test been at Watkins Glen for lap times, the 962 would have cleaned the Monte's clock.
     
  6. jmarti445

    jmarti445 Senior member

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    If it has 450HP and a lower final drive on the transmission it may do 180MPH. The civic is a light car, my 2008 EX does close to a buck 130 stock, I believe the governor is set to 127MPH and I've seen cars without governors do close to 230 kilometers per hour. The Si's rev to 8500 RPMs. The RSX was a great example of this.
     
  7. jmarti445

    jmarti445 Senior member

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    Get the guy to prove it, talk is cheap
     
  8. twinrider1

    twinrider1 Diamond Member

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    This thread should have been locked after the first 8 words.

    Zero effect on top speed. It affects the time needed to get to top speed.
     
  9. skyking

    skyking Lifer

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    zero is a really small number so I'd rather say not much :D
    Here is a handy calculator that will give you the horsepower used by rolling resistance and aerodynamic resistance, all the way to 200 MPH!

    http://ecomodder.com/forum/tool-aero-rolling-resistance.php
    Drop some numbers in and you can see as that Aero drag rises exponentially, the rolling resistance drag just moseys along up a shallow slope.
    At the end at 200 MPH with the example numbers, aero is 370 hp and rolling resistance is 7.81 hp :p :D

    You can find numbers for your car on the web, take a guesstimate on crr. I use .011 for typical tires.
     
  10. JCH13

    JCH13 Diamond Member

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    Taking a known comparable:

    MS3 = 263hp,155mph top speed (gear-limited, so this is conservative)

    Power required for aero drag is quadratically related to speed: (180mph^2)/(155mph^2) = 135% power requirement to go 180mph

    263hp*1.35 = 355hp

    Should be doable with 450hp assuming the car is not gear-limited.
     
  11. JulesMaximus

    JulesMaximus No Lifer

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    Would that car even be stable enough to drive safely at that speed?
     
  12. skyking

    skyking Lifer

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    Race cars generate a shit-ton of downforce for handling. That induces even more drag.
    I'd say no, not safe in any stock aero form.
     
  13. JCH13

    JCH13 Diamond Member

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    A little bird told me it wouldn't be crash-worthy at 3x the design speed (8x the energy) of the crumple zones...
     
  14. skyking

    skyking Lifer

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    Fatality!
     
  15. DaTT

    DaTT Garage Moderator
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    I had a hard time believing him because he also told me a 400hp civic can do low 8's. 1/4
     
  16. JackBurton

    JackBurton Lifer

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    lol!
     
  17. Throckmorton

    Throckmorton Lifer

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    Weight is irrelevant but why wouldn't it do 180mph? 450hp is a lot of horsepower and Civics are very aerodynamic.

    But I'm guessing his tires aren't rated for that speed, and the aerodynamics will make it dangerous. No, a wing on the trunk doesn't help!
     
    #17 Throckmorton, Jun 8, 2012
    Last edited: Jun 8, 2012
  18. Pulsar

    Pulsar Diamond Member

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    Hard to say. Probably not. The problem is usually rear downforce. The front usually has a pretty decent amount just because of the hood slope. Most cars at that speed form a suction as the air flow lifts off the rear window (Bernoulli number, no longer laminar flow, etc...).

    The '04 era Mustangs are limited to the speed they are exactly because of that reason.
     
  19. Pulsar

    Pulsar Diamond Member

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    Um... actually a wing on the trunk DOES help.
     
  20. JulesMaximus

    JulesMaximus No Lifer

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    I've owned 2 Mustangs and neither one of them felt safe at speeds over 130mph. They get really light in the rear.

    Adding a rear wing will help but also creates drag that will further limit top speed.
     
  21. Doppel

    Doppel Lifer

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    V-TEC, anything is possible, crate motor from Japan [overnighted], double-clutching, beef the welds on the manifold etc. it might happen!

    In truth can a FWD on the planet even do 8's? Obviously it would need literally magnitudes more than 400 horsepower, but I question whether it could get the traction. A 1000 HP bugatti veyron with AWD does 1/4 in 10 flat.
     
  22. Ferzerp

    Ferzerp Diamond Member

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    Gotta avoid that danger to manifold.
     
  23. JulesMaximus

    JulesMaximus No Lifer

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    Apparently they can.

    http://www.youtube.com/watch?v=ct36IUKaP5w
     
  24. LTC8K6

    LTC8K6 Lifer

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    The trunk lid is not the place for a lot of weight.
     
  25. Throckmorton

    Throckmorton Lifer

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    Yes, it helps traction at the rear, but it will also lift the front