if torque gives you thrust so that you can accelerate quicker (i think), then what is hp good for? I dont really completely understand the two. Can someone clarify?

 

hp gives you top end speed ...
and torque tells you how fast you are going to get there ...

sounds right?

 

Horsepower= Torque X RPM/5252. Horsepower is a measurement of the rate that torque is being applied at a given rpm. Horsepower and torque are not two seperate things...rather they are related.

 

I think that another big thing people forget is that the torque that is measured for our cars on a dyno is a 1:1 ratio. The reason a Honda S2000 with only 153lb/ft of torque can beat a car with more torque is because of things like weight, wheel circumference, gear ratio, redline, etc. You have to take all of that into effect.

I don't remember the exact mathematics, but I saw someone do the calculations once for an S2000 vs 2000 Mustang GT. With the gearing ratio, wheel circumference, etc taken into consideration, the S2000 puts out around 1050lb/ft of force, to the GT's 980lb/ft of force (the numbers were somewhere in that area) and calculating that, with the weight, at that particular rpm for each car, the S2000 is accelerating 5.5ft/second sqaured.... and the mustang at 5.1ft/second squared.

 

[QUOTE]Originally posted by s2000crazy
[B]if torque gives you thrust so that you can accelerate quicker (i think), then what is hp good for?

 

Torque makes you accelerate.
You accelerate until the torque peak, after that you must shift.
The more horsepower you have, the higher the torque peak.
A car with not much horsepower (relative to its torque) can only go to a certain RPM until it stops accelerating.
A mustang GT still has more horsepower than the S2000, but because we have so much more horsepower relative to our torque, it makes our torque peak extremely high (7500 vs. about 4500)

 

forgot to say, this means that you can't just increase the redline of any car to make it faster, because the torque peak is still going to be the same.
I'm pretty sure this is where cam lobe profiles come into play.

Please correct me if I'm wrong on any of this.

 

This is the correct answer as some of you have hit upon. Hopefully, I'll be able to explain it clearly.

Torque to the wheels = how fast you'll accelerate at any instant (this is the punch you feel with high-torque vehicles). It doesn't mean how fast you'll accelerate over a period of time; that's where HP comes in to play.

Because HP is correlated with torque through RPM as Station pointed out, given the same torque curve, a car with lower HP will have to shift at a lower RPM than a car with higer HP.

Shifting to a higher gear means that you put down less torque to the wheels than you would have if you stayed in that lower gear because of the loss of mechanical advantage. (Pedaling a bicycle in high gear is much harder than in low gear.)

For a real-life example, my Grand Cherokee's high-torque means that its maximum instantaneous acceleration is greater than that of my S2000. However, due to my Jeep's lower HP, I cannot sustain that acceleration very long and must shift to a higher gear much more quickly than my S. This shifting reduces the torque I put to the wheels, which reduces the acceleration.

 

[QUOTE]Originally posted by Incubus
[B]Torque makes you accelerate.
You accelerate until the torque peak, after that you must shift.
The more horsepower you have, the higher the torque peak.
A car with not much horsepower (relative to its torque) can only go to a certain RPM until it stops accelerating.

 

So you're saying that if a mustang's rev limiter was simply raised, then it would have more horsepower than it currently has?

I am implying that if the torque peak is at a high RPM, then the horsepower is high.(If the torque peak is at a low RPM, then the horsepower is low)
A high rpm (redline) has nothing to do with how much horsepower you've got. A high torque peak gives you more relative HP.

Sorry, I just phrased it incorrectly in the first thread.