You have to know the rpm. Ideally you want to maximize torque in the rpm range the engine will be used and you'll have the power you need. I've worked on engines that made over 5,000hp, but at such a low rpm that the engine at that power level was producing nearly 100,000lb-ft of torque. Knowing horsepower without knowing what rpm it's produced is meaningless.

Anyone interested in truely understanding the realtionship between horsepower and torque should read those links. As far as automobile performance, it gets a bit more complicated as you have to start using the higher hp at higher rpm, which is less total torque, with the proper gearing that the extended rpm allows to multiply the smaller amount of torque into a larger one at the wheels. That's why some low geared sports cars with good hp but crap for torque are just as fast or faster than cars with equal hp and more torque for similar vehicle weights.

You can build a 302 and a 347 with the same horsepower, but the 347 will have more torque. The 302 will turn higher rpm and can use a lower gear and have the same total speed in each gear, and in the same car they may run the same time at the track. And both may drive the same on the street.

 

I like whichever number is higher. My car makes (insert number) of (torque/horsepower)!!! For me its torque right now. keep in mind this is usually said at school or work when I am not driving, if Im in the car I just stomp the gas and wait for the smoke to clear so I can see the guy in my rearview mirror...or not
Kip

 

I'm with 67mustang302. Horse power and torque are one thing, but then you throw a car into the equation and you have gearing, traction, vehicle weightand a whole lotta other things to think about.

 

Man there is a lot of misinformation out there. I have heard that torque is what puts you back in your seat and horsepower is torque at high rpm. That is compete bs. Here is a quick physics lesson. Torque is a measurement of force (specifically rotational force). Horsepower is a measurement of power (the rate that energy is transmitted or work is done). Those are two different measurements of two different things that are related and proportional. Others above have saidabove, andthey areright, in that horsepower ismeasured from torque force at a given rpm. Now which is more important...That is an unanswerable question because theylinked and proportional. What you should ask is at what point should I shift tomaintain maximum acceleration. That can be obtained via running a spreadsheet or a shift point program. I can prove it to you mathmatically, but it is probably going to be your engine's redline. If the shift points are too highfor your liking, then you need a camthat will peak horsepower/ move your torque curve lower in the rpm band. You may ask how much is enough peak horsepower or how much torque do I need at a give rpm. As said by superdavid, that depends on many many factors like gearing, transmission gearing, weight, etc and is not easy to quantify. It is probably best to get the most torque you can afford and the power curve should be as wide as you can afford. How wide and how tall your torque curve is only depends on the quality of the parts you can afford and the design of the engine you build. At some point, you have morepower than your suspension and tires can deal with.IMO, that is the right amount!

Here is a website talking about torque, horsepower, and shift point.

http://www.allpar.com/eek/hp-vs-torque.html

 

Thank you guys for making this more complex than I care to read right now. All I know is that when I hit the gas, I like the feeling of being planted in my seat. When the planting quits (usually around 3500) it's time to shift. Think I need a bigger cam...or a heavier foot.

 

Torque wins races,not horsepower. Enough said.

 

you win the smartest man in the universe award. I get so sick of these threads with people fighting back and forth over the whole thing.

remember guys, torque is a power measurement in rotational physics. hp is the linear calculation thereof. a motor CANNOT make hp, it makes torque, and its power as calculated from that.

i could get down into it, but as it turns out, as far as sheer acceleration ability goes, high end torque (what you guys are calling peak hp) is better able to accelerate a vehicle than low end torque on a logrithmic scale. theoretically anyways. in practice you cant go fast if you cant even get ur car moving from the standstill.

 

torque= N*m (newton meter), is a newton, measurement mass*accel = mass*meter/second squared times meters, or mass*meter squared/ second squared. power is work/time. work is F*distance, or mass*meter sq/ sec sq over time. so power is torque/time. they are related by rpm and a constant (5250). rpm is revolutions per minute, which in terms of units is 1/minutes, or 1/time. so multiply torque by rpm you get units of power. this is just an elaboration of what cowboy is saying. and i guess for what i had previously said to be MORE correct i should have said that power is a linear functional calculation of torque, not just linear calculation since they do have different units (namely 1/T)

 

Well, since you put it that way...wouldn't HP be the force that the piston is driven down with and torque that which is trnsfered to the crank?

 

that wouldnt be the motors output, but yes, there is a power rating associated with the speed at which the piston is driven down. this information has no practical use however.