Maybe its just me, but car forums seem to be loaded with some false info. Im just gonna throw some out there that bug me. Feel free to add your own or elaborate.

HP/TQ - This one bugs me. VERY few people seem to understand HP and TQ. After alot of reading I finally feel like I fully understand it. TQ is what accelerates a car, HP is what determines how you use the TQ. If you are confused about it, you can start with these formulas...

Engine TQ x Tranny ratio x Rear ratio / tire radius = Force (used to accelerate)

Physics teaches us F=MA

So Engine TQ x Tranny ratio x Rear ratio / (tire radius x mass of car) = Acceleration

Horsepower comes into the equation when you throw speed into the equation

HP = TQ x RPM / 5252

Now Put HP into the Acceleration Eqn:

[HP x 5252 (constant) / RPM] x Tranny ratio x Rear Ratio / (Tire radius x Mass of car) (constants) = Acceleration

Because tire radius, mass of car, and 5252 doesnt change, we can take them out and leave them as constants

Acceleration = (HP/RPM) x (Tranny x Rear) x c

Now speed = RPM / (Tranny x Rear ratios) x [2pi x tire radius]

Combining Speed and Acceleration formulas, it is easy to see that:

(HP/Speed) x constant = Acceleration



I just thought I would clarify exactly how HP and TQ come into play when a car is accelerated. Many people fail to understand the basic concepts that it takes more HP to accelerate mass at a faster speed and therefore acceleration is simply a product of TQ and gear ratios (along with constants).

Just study those equations that I derived and learn them. You will get a better understanding of cars and how power and TQ affect a car. It will help you better understand the effect of gearing and powerbands of motors. You can also see how a TQ converter multiplies acceleration off the line.

Sorry about the long post, I was just bored with school (studying orbits gets boring REAL fast) for a bit and wanted to waste time with my Ti-89

 

Here's my simplified view of the whole thing:

TORQUE is the amount of work that can be accomplished.
HORSEPOWER is the speed at which that work is accomplished.

Everyone seems to forget that only TORQUE is measured on a dyno, and horsepower is then CALCULATED from torque and RPM.

 

Here we go agian.

It's about time for this again, isn't it? Yes, it's a good topic to discuss. You may get a few (?) differing opinions. disco192, you are on the right track, but that you "fully understand it" might be an very slight exaggeration.

FWIW: Yes, F=ma applies. That's going to be the difficult part to remember as this thread goes where most have gone in the past. The "F" is the (thrust) force applied to the chassis by the drive tires. This is an opposite reaction to the force at the tire/road contact patch, which depends on the axle torque and rolling radius of the drive tires, as well as load and tire fricton coefficient, sometimes referred to as "bite" or simply "traction".

This much is intuitive to many, but not all, folks. However, this is just an instantaneous or "static" look at it. As soon as the vehicle moves, we have a "dynamic" condition, so we need to look at the rate at which the torque is applied. Here is where "power" comes into play, and where this type of thread usually diverges.

My $.02.

Let the games begin...

 

4800 lb Lightning....crappy aerodynamics....

414 STD rwhp....509 STD rwtq

111.3 mph...

Torque moves mass..

 

Actually, horsepower is an amount of work (by definition)
Torque is a force. No motion (work) is implied.

 

Actually horsepower moves mass......1 hp = moving 33,000 lbs 1 ft in 1 minute
Torque is what gets it going and hp is what keeps it going. The faster you go the less torque is applied. That why it is hard to spin the tires at 150mph

 

Yeah...tell me how much horsepower does it take to move a 4800 brick to 111.3 mph in the 1/4?

 

Chrome dipsticks and big heavy fart pipes don't care - they just make it FAST!

 

well you said 414 rwhp so i'll take your word for it

 

I can't believe I screwed that up. I should know better than that. DOH!!! You're right, horsepower is work, and torque is force. Lots of torque at a low RPM = a lot less WORK being done than lots of torque at a high RPM. I like to use the Semi as a basis of comparison. Take a 400 HP diesel engine and compare that to a 400 HP LT-1. The diesel can move 80,000 plus pounds, but it takes a very long time to accelerate that weight. However, it has enough torque to accomplish the task. On the other hand, the 400 HP LT-1 would have a very hard time moving the same load, and I highly doubt it would be able to pull that load(if it could even get it moving) to a decent speed. These are merely my perceptions, so please don't take them as the absolute truth.

 

HP is the rate at which TQ is applied.

 

Horsepower is not a rate. A rate is distance over a period of time. HP is moving a certain weight at a certain rate. Horsepower is calculated from torque on a dyno but is not a result of torque.

 

Well, actually:
Torque is force which accelerates the mass.
Work is done when a mass is moved through a distance, it can take any time to do it and the work is the same.
Power is the rate of doing work, so moving your 4800lb monster 1/4 mile is a fixed quantity of work, but how fast you do it is related to the power required.

 

Do I have to say it again?
HP is how fast you hit a wall. TQ is how hard you go through it.

 

Im not exactly sure that TQ is what is measured. I cant really say because I dont know the inner workings of a dyno, but TQ is multiplied by the gear ratios and has many factors. A larger tire will change the force applied upon the dyno.

If you relied completely on the dyno wheel and had no idea about RPM of the motor, you could still calculate HP. Without RPM or knowing all the gear ratios, you couldnt calculate the TQ at the motor.

Just thinking out loud.