View Poll Results: HP -> Acceleration... not Torque!
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HP -> Acceleration... not Torque!
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From: Motor City
[QUOTE]Originally posted by FYRHWK1
[B]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.
[B]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.
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From: Rochester
Well, I had a lengthy post all ready, but realized that:
(1) I think it has all been said a number of times in this thread by myself and others, and
(2) I suspect long posts are often left unread.
Instead:
(A) I too apologize if I came down too hard in my last post.
(B) If you really want to get to the answer, re-read this entire thread! (well, ahem, at least, ahem, my posts
)
(1) I think it has all been said a number of times in this thread by myself and others, and
(2) I suspect long posts are often left unread.
Instead:
(A) I too apologize if I came down too hard in my last post.
(B) If you really want to get to the answer, re-read this entire thread! (well, ahem, at least, ahem, my posts
)
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From: Motor City
Originally posted by FYRHWK1
Well, I dont know what to say, if you dont think you accelerate harder in first over second then i guess we're at a standstill. Do this, go launch normally in first, then try it in 4th or 5th without slipping the clutch, why do you take off harder (at the same RPMs) in first then you do in the higher gear? Why do you probably stall in the higher gear? because the effective wheel torque in the higher gear is much less, at that RPM with the little inertia you've got going in the engine the resistence from the car and ground overpowers the wheels torque, so you stall.
Well, I dont know what to say, if you dont think you accelerate harder in first over second then i guess we're at a standstill. Do this, go launch normally in first, then try it in 4th or 5th without slipping the clutch, why do you take off harder (at the same RPMs) in first then you do in the higher gear? Why do you probably stall in the higher gear? because the effective wheel torque in the higher gear is much less, at that RPM with the little inertia you've got going in the engine the resistence from the car and ground overpowers the wheels torque, so you stall.
You continue to interchange these to words, at will, to try to prove you point.
Do not confuse the work you do to create a force with the work done by the force you create; they are not the same.
[QUOTE]Originally posted by FYRHWK1
[B]
You accelerate with your torque curve (if you believe like I do) because the wheel torque follows that curve, only in a multiplied form, you don't accelerate harder as HP rises,
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From: Houston
[QUOTE]Originally posted by FYRHWK1
[B]
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)
[B]
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)
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From: Houston
OK, my previous post finally made me realize what is absolutely the simplest way to explain why is it the HP that accelerates your car.
Wheel torque accelerates your car. Everyone (even the most stubborn "torque enthusiasts") will give you that.
Since WheelTorque = EngineTorque*Gearing, and Gearing = EngineRPM/WheelRPM, and EngineHP = EngineTorque * EngineRPM, we get that:
WheelTorque = EngineHP/WheelRPM
At any given speed, there's nothing you can do to change your wheel RPM, so your wheel torque (and thus your acceleration) is DIRECTLY proportional to the engine HP at that RPM.
I really cannot think of a simpler way to explain this.
Wheel torque accelerates your car. Everyone (even the most stubborn "torque enthusiasts") will give you that.
Since WheelTorque = EngineTorque*Gearing, and Gearing = EngineRPM/WheelRPM, and EngineHP = EngineTorque * EngineRPM, we get that:
WheelTorque = EngineHP/WheelRPM
At any given speed, there's nothing you can do to change your wheel RPM, so your wheel torque (and thus your acceleration) is DIRECTLY proportional to the engine HP at that RPM.
I really cannot think of a simpler way to explain this.
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From: Portland
A CVT illustrates the difference between torque and HP very well. With standard fixed ratio gearing the peak acceleration will occur at the torque peak. But as Zoran pointed out CVTs operate at the HP peak and do in fact create the most wheel torque that way. Weird huh?
With a CVT peak HP is king and the torque curve does not matter. Given a given wheel speed the peak wheel torque will always occur at the engine's HP peak.
(Wheel torque = Engine HP / Wheel RPM)
However instead of finding the peak wheel torque at a fixed speed, calculate the maximum wheel torque for a fixed gear ratio:
(Wheel torque = Engine Torque * gearing)
It occurs at the torque peak, not the HP peak. Also, If you were to graph the wheel torque curve it would look like the engines torque curve but shifted up or down depending on the gearing. Which means that the way the car feels as it accelerates would look like the torque curve.
So based on these two examples I can see two things: peak HP is the best indicator of theoretical performance (Or actual given a CVT), but an engine's torque curve looks like the wheel torque curve unlike an HP curve. And with a standard transmission it is still important for indicating performance.
The peak torque figure for the engine is nearly useless. The only thing you can get from that is some sense of how high the engine revs, but it tells you almost nothing else. I have no idea why automotive magazines coninue to print that statistic. A number for peak HP and a torque curve would be the most useful.
With a CVT peak HP is king and the torque curve does not matter. Given a given wheel speed the peak wheel torque will always occur at the engine's HP peak.
(Wheel torque = Engine HP / Wheel RPM)
However instead of finding the peak wheel torque at a fixed speed, calculate the maximum wheel torque for a fixed gear ratio:
(Wheel torque = Engine Torque * gearing)
It occurs at the torque peak, not the HP peak. Also, If you were to graph the wheel torque curve it would look like the engines torque curve but shifted up or down depending on the gearing. Which means that the way the car feels as it accelerates would look like the torque curve.
So based on these two examples I can see two things: peak HP is the best indicator of theoretical performance (Or actual given a CVT), but an engine's torque curve looks like the wheel torque curve unlike an HP curve. And with a standard transmission it is still important for indicating performance.
The peak torque figure for the engine is nearly useless. The only thing you can get from that is some sense of how high the engine revs, but it tells you almost nothing else. I have no idea why automotive magazines coninue to print that statistic. A number for peak HP and a torque curve would be the most useful.