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Thread: Question about bhp, torque weight, etc

  1. #1
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    Default Question about bhp, torque weight, etc

    Right..simple one(!?!) this..

    If you take two identical vehicles (say car or bike). You give vehicle 2 exactly twice the bhp, twice the torque and twice the weight. Vehicle 2 has identical engine characteristic curves to vehicle 1 (e.g. peak bhp at say, 7000rpm, etc...)

    Is car 2 any 'faster' with regards acceleration and top speed?

    I think I know the answer, but thought I would put it out to the floor...

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    Regular Member VVT-i-MATT's Avatar
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    Ahh, it's one of those, "will a plane take off on a treadmill" questions!

    I like.

    "Common sense" says they will be identical.

    I would say the heavier one though would be slower accelerating, and a lower top speed. Weight on the tyres would increase friction on the road which the lighter vehicle wouldn't have a problem , also it's a higher mass to overcome inertia..

    So in essence, light car wins!

    Just my thoughts though.
    Last edited by VVT-i-MATT; 22nd March 2012 at 14:51.

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    Vehicle : vectra

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    Default

    i would say the heavest car will be quicker as it has more grip but if u had a good driver in the lightter car i would be leaning towards the heavyer car
    Vectra vxr custome remaps egr deletes dpf and diagnostic work all remaps are custome bench tuning avalible all genuine equipment PM for info

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    Moved from Gen Chat to the aptly titled "Tuning" section

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    Default

    lighter car faster as the clutch would slip on the heavy car

    also bigger loss of power due to friction through bearings and would suffer more at higher speed / wind resistance

    and agree to overcome the initial inertia is a major power sapping element if the clutch wasnt an issue

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    VIP-Member Z80's Avatar
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    Default

    Inertia management is where the higher torque would act, though.

    I agree on the clutch slip, but here again, there are remedies for that on performance cars, such as double clutches, etc.

    Anyway, just try to catch up with a turbo diesel if you ride a petrol car : the diesel would probably always lead at first because of its huge torque, despite being heavier.

    The petrol car will catch up afterwards, as diesel engines torque and power quickly reach their maximum, then even drop down at about 5000 rpm, while petrol engines go on increasing power again and again while increasing rev.

    When I leave a parking space in a street, I'm driving in 5th gear already 50 meters away. Just try to do that with a petrol car...

    Otherwise, on same type of engines, the lighter the car, the quicker the response, of course.

    There's a video floating around YouTube showing a Holden Commodore racing against a Ford Mustang (if I remember well), and the Commodore is completely left behind from the start.

    But I think the Commodore's automatic transmission (plus of course the beast's 2 tons) is mostly responsible from that. Despite the manual clutch actually being prone to slip if you don't take it easy, automatics are still worse (though Audi claims to make miracles on this point - at least according to a seller I talked with )

    OK, now you know I HATE automatic transmssions, unless someone proves me wrong... LMAO

    Anyway, it wasn't an HSV, not even talking about a V8 Supercars racing prepared model, but a quiet all-around Commodore. I've heard about a season that had been opened to foreign cars, and not so surprizingly, Holden HSV Commodores and Ford Falcons made them ridiculous, despite their 2 tons, so I think that, yes, their monstrous torque and horsepower did make the difference. Not even talking about australian tracks in the bush wrecking the poor fragile japanese and european cars, while the aussie V8 monsters are built like panzers, hence their weight...

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    I would expect the heavier car with twice the power/torque to be faster at top end as aerodynamic loading would be more important there.

    The friction would be higher for the second vehicle as stated but would not double because the pressure in the bearing would only be increased over a portion of the bearing, i.e. the top and bottom.

    The smaller car may move off quicker if we are taking into acount grip on the road and the clutch.

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    I don't think the weight to bhp/torque ratio is quite as simple as that.....

    double the weight doesn't really matter once the vehicle gets moving..... and once moving it'd propbaly be a case of 1st, 3rd, 5th, 6th in the gears as all the extrfa torque would allow block changes........

    I reckon anyway lol

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    My take on this is that..

    The smaller vehicle would be faster off the line as it has less inertia and not a huge amount of power is needed anyway to get off the line

    Acceleration on both vehicles would be the same up until, say 50 ish (when wind resistance come into play), after which the bigger vechile with its greater torque and power would allow it to pull a higher top speed and accelerate quicker

    Around corners the lighter vehicle would be faster (assuming both vehicles can enter the corner at the same speed). On exit the car with more power would be able to accelerate away with more’ umff’

    The lighter vehicle would be able to brake later and harder

    So more bhp/torque would give you more top-end or acceleration beyond say 40mph, and not really much else (everything being equal, or course)

  10. #10
    spoons
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    I would say that the second vehicle (twice the weight and power) will be at the highest speed

    However, the resistance from wind is massive. At 170 mph I can feel it pushing against the car like mad. So more power = greater impact on overcoming wind resistance

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