Clearing Up Confusions about Torque and HP

Hi all,

It has come to my attension how many arguments result between high revving low torque engines and low revving high torque engines. I just want to lay out an example to clear it up.

Givens:
(Max accel occurs at peak torque in each gear)
Tire Diameter: 24 inches
Tire Circumfrence: 6.28 ft
Engine 1: 550ft-lbs @ 2500rpm
Engine 2: 185ft-lbs @ 7500rpm
Cars have equal mass

Neglecting actual gear ratios and assuming peak torque occurs at given MPH (ideal gears)

Test Speed: 40mph
Tire Rotation: 560rpm

Engine 1:
Engine to tire ratio (4.46:1)
Torque to rear tires: 2453 ft-lb
Accleration force: 2453.2 lbf

Engine 2:
Engine to tire ratio (13.38:1)
Torque to rear tires: 2475.3 ft-lbs
Acceleration force 2475.3 lbf

Result: Engine 2 has greater acceleration

This is just an example to show that you cant compare engines purely on peak torque without considering the rpm which it occurs because the end result is the acceration force at the rear tires and that is what really matters.

Yes, i know you have to consider gear ratios and other things in real life but this shows that acceleration of a vehicle is only related to the force at the rear tires and the mass of the vehicle.

(i thought this might help some folks when arguing a point)

RE: Clearing Up Confusions about Torque and HP

which is why hp is a mathematical derivation based on torque and rpm.

550 * 2500 / 5250 = 261.9 hp

185 * 7500 / 5250 = 264.3 hp

You just showed that a car with more hp will have better peak accleration.

RE: Clearing Up Confusions about Torque and HP

Screw HP baby...it's all about nice beefy midrange torque for "real world" driving. My ZX9R made 142HP tuned, and roughly 70TQ...but at well over 8,000RPM. My VTR1000 made 104HP, with a whopping 72TQ at a mere 4,500. 50TQ was available right off idle!!! The Honda S2000 it cool, but please....you have to rev the living daylights out of it to make it go. God forbid it you just put the pedal down with no downshift....

RE: Clearing Up Confusions about Torque and HP

which is why hp is a mathematical derivation based on torque and rpm.

550 * 2500 / 5250 = 261.9 hp

185 * 7500 / 5250 = 264.3 hp

You just showed that a car with more hp will have better peak accleration.

Click to expand...

I know this dave, but i just wanted to define this for those who make stupid arguments with no basis for thier point of view.

RE: Clearing Up Confusions about Torque and HP

Screw HP baby...it's all about nice beefy midrange torque for "real world" driving. My ZX9R made 142HP tuned, and roughly 70TQ...but at well over 8,000RPM. My VTR1000 made 104HP, with a whopping 72TQ at a mere 4,500. 50TQ was available right off idle!!! The Honda S2000 it cool, but please....you have to rev the living daylights out of it to make it go. God forbid it you just put the pedal down with no downshift....

Click to expand...

Yes ron, but which bike has greater acceleration? This was my point.

i agree for different types of driving a broad torque band would be beneficial.

RE: Clearing Up Confusions about Torque and HP

Here is another question for you guys..

In a standard transmission peak acceleration occurs at the peak torque.

What would give the greatest acceleration in a Continuously Variable transmission, if the engine was at peak torque or peak hp during acceleration?

RE: Clearing Up Confusions about Torque and HP

This also shows how rediculuous it is when people brag about their peak hp and torque numbers. What matters in a race (Besides driver skill) is the average hp/torque from launch to the shift point.

RE: Clearing Up Confusions about Torque and HP

it'd accelerate faster at peak hp because the gear ratio would be more favorable at a given road speed.

Leo's right, it's really the area under the curve that counts in the end, for most people.

In a race engine that is going to spend most of it's time in the upper RPM ranges, torque isn't so important, just peak hp. For a street engine, the peak hp is important for a lot of people, but torque is more of a factor.

RE: Clearing Up Confusions about Torque and HP

well put dave

RE: Clearing Up Confusions about Torque and HP

it is all about the curve not the peaks.

RE: Clearing Up Confusions about Torque and HP

We talking about HP and torque still?

RE: Clearing Up Confusions about Torque and HP

Torque lets you leave long strips of rubber on the road, and gets you tickets for reckless endangerment.

Horsepower makes big numbers on the speedo, and gets you tickets for speeding, fleeing and eluding.

Choose your poison.

Bob