View Poll Results: HP -> Acceleration... not Torque!
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HP -> Acceleration... not Torque!
Registered User
Joined: Mar 2001
Posts: 1,455
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From: Farmington Hills
It seems to be that we have two camps. One believes that torque at low RPM is beast and the other that says that high RPM torque is the best. Well, it all depends on what the car was designed for. If you want to get off the line or tow with, you want torque at low RPM's. If you want a car that is fast around a track, high RPM torque is what you want.
If you used motorcycles as an example, you also have to look at the weight of the vehicle. The less weight it is, the less torque you need. Why do you think an 18-wheeler has tons of torque? It weighs more and thus needs more. Look at the power to weight ratio of out car compared to a motorcycle. A motorcycle generally has more torque per lb as well as HP per pound.
All in all, HP and torque are both important. Where there are in the power band is important to different applications.
Lance
If you used motorcycles as an example, you also have to look at the weight of the vehicle. The less weight it is, the less torque you need. Why do you think an 18-wheeler has tons of torque? It weighs more and thus needs more. Look at the power to weight ratio of out car compared to a motorcycle. A motorcycle generally has more torque per lb as well as HP per pound.
All in all, HP and torque are both important. Where there are in the power band is important to different applications.
Lance
Registered User
Joined: Jan 2002
Posts: 250
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From: Redford, MI
[QUOTE]Originally posted by Destiny2002
[B]
On level ground, The amount of road horsepower required to maintain a vehicle's speed is the sum of all frictional losses, the additional provided from the engine will accelerate the vehicle.
[B]
On level ground, The amount of road horsepower required to maintain a vehicle's speed is the sum of all frictional losses, the additional provided from the engine will accelerate the vehicle.
Registered User
Joined: Jul 2002
Posts: 163
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From: NY
First of all, disregard my previous post, i wasnt in a very good mood while writing it, my apologies, flamebait isn't necessary.
Secondly, downshifting to put you in your HP band? regardless of your HP band you accelerate following your torque curve, case in point the ford CVT transmissioned fiesta will rev up to it's torque peak (not HP peak as someone preiviously stated) and then STOP the engine there, that is the highest point of engine output possible, from there the transmission will start widening the gear ratios until you've reached the topspeed (this is of course under full throttle)
Now if the HP peak were the point of maximum acceleration, why would they do that? I'll fully admit i'm not capable of arguign on a mathematical level, i've only just started my college degree and while it's fairly easy to understand, i'm not at the point to do it yet. I can however argue this, you both claim acceleration = hp/(m*v) this is completely wrong, it takes no account of gearing into the situation. Do this, accelerate in 1st gear, up until redline then do it again in 2nd, you've gone through the EXACT same powerband yet one accelerates you harder, why? torque multiplication.
My example of revving from 4000 in 3rd and 5th is perfectly legitimate, the aerodynamic drag difference is not that big and if you placed your car in vacuum it would STILL accelerate harder in 3rd due to the greater mechanical advantage, not because of any HP differences. granted, you can only accelerate as fast as you move up your RPMs, thats a given as you can only go as fast as your wheel RPM lets you, however you need the torque to overcome drag and friction and to push the car forward, the more torque the easier it is to overcome this, and thats why accelerate harder if you add torque by either downshifting, shorter ratios or by increasing engine torque output.
As for HP determining your topspeed, wouldn't the cars ability to overcome drag (torque) and wheel RPM be the determining factor there? pushing aerodynamics aside as long as you dont flip or run out of traction, drag can be overcome by more torque and more topend by wheel RPM, I wouldn't think HP has anything to do with topping out.
If you want to be fast, having a long, wide powerband without any dead spots is what you would want. After all unless you can build the engine around the track you've no idea if you'll be operating in the upper or lower end of your powerband. Personally, i'll take a torque band from around 2000 on up until redline, keeping ~80-85% of it seems to be average these days and thats really not bad, it lets you stay in the powerband easily and keep from bogging out of turns, but we're getting off topic.
Nay, that's all about inertia. Case in point, putting a heavier flywheel in a drag car will help it's 60' times, why? because the greater amount of energy stored in the heavier flywheel will help the wheels get moving as it'll take more resistence from them to stop the engine from turning. Thats also why you see a car launch better from higher RPM, it isn't because of the HP powerband being higher, it's because the engine has more energy for the wheels to try and stop. I do believe the calculation for inertia is m*v squared, i really need to get a notebook and start writing these down. . .
Secondly, downshifting to put you in your HP band? regardless of your HP band you accelerate following your torque curve, case in point the ford CVT transmissioned fiesta will rev up to it's torque peak (not HP peak as someone preiviously stated) and then STOP the engine there, that is the highest point of engine output possible, from there the transmission will start widening the gear ratios until you've reached the topspeed (this is of course under full throttle)
Now if the HP peak were the point of maximum acceleration, why would they do that? I'll fully admit i'm not capable of arguign on a mathematical level, i've only just started my college degree and while it's fairly easy to understand, i'm not at the point to do it yet. I can however argue this, you both claim acceleration = hp/(m*v) this is completely wrong, it takes no account of gearing into the situation. Do this, accelerate in 1st gear, up until redline then do it again in 2nd, you've gone through the EXACT same powerband yet one accelerates you harder, why? torque multiplication.
My example of revving from 4000 in 3rd and 5th is perfectly legitimate, the aerodynamic drag difference is not that big and if you placed your car in vacuum it would STILL accelerate harder in 3rd due to the greater mechanical advantage, not because of any HP differences. granted, you can only accelerate as fast as you move up your RPMs, thats a given as you can only go as fast as your wheel RPM lets you, however you need the torque to overcome drag and friction and to push the car forward, the more torque the easier it is to overcome this, and thats why accelerate harder if you add torque by either downshifting, shorter ratios or by increasing engine torque output.
As for HP determining your topspeed, wouldn't the cars ability to overcome drag (torque) and wheel RPM be the determining factor there? pushing aerodynamics aside as long as you dont flip or run out of traction, drag can be overcome by more torque and more topend by wheel RPM, I wouldn't think HP has anything to do with topping out.
It seems to be that we have two camps. One believes that torque at low RPM is beast and the other that says that high RPM torque is the best. Well, it all depends on what the car was designed for. If you want to get off the line or tow with, you want torque at low RPM's. If you want a car that is fast around a track, high RPM torque is what you want.
This is why you must create significant slippage at the clutch or at the drive wheels for a good launch with a manual transmission. In an automatic, it's as easy as flooring it.