JP66

So as a newbie I am constantly absorbing new information, and recently I have read and also been involved in discussions that brought up the topic of Torque, Horsepower, and acceleration. I am active in other forums and I am known as somewhat of a loud mouth trouble maker every where else except here . . . so I figure what the heck . . . time to make my mark here . . .

So here it goes . . .

Torque is the only thing that matters to acceleration. Now prove me wrong!


This may take a while and I may need multiple pages so give me a chance to lay out all my logic before jumping all over me, but I will say that when I am proven wrong, I am ALWAYS willing to say "I was wrong."

Anyways lets start with some simple definitions




Force = Mass x acceleration

so

acceleration = Force / Mass

Torque is a measurement of Force


now lets talk about Power

Power = Work / time and
Work = Force x distance (that ones debatable but that's a whole other forum)


Horsepower is a measure of POWER


let me say that again . . . .


Horsepower is a measure of POWER

and

POWER is WORK / time and WORK is FORCE x distance.


The crux of the issue here is that HP increases with RPM because the car is turning faster and so doing more work in less time. (The wheels are turning faster so the car is traveling more distance.)

Horsepower is measuring work you're doing over time and the faster the engine turns the more work it does.


BUT

acceleration has nothing to do with Horsepower. Acceleration is a product of the Force applied to the wheels.


Let's take a look at 3rd gear and 4th gear in a 987 at 5000 RPM.

First 3rd gear.

Torque at the Wheel = Engine torque x Gear Ratio x Differential ratio

so for a 987 (I'm guessing on the diff number but it really doesn't matter to the relativitiy of the argument)

First 245 ft*lbs = 333 Nm so

333 Nm x 1.41 (3rd gear ratio) x 4 (diff ratio) = 1878 Nm

so the Torque at the Wheel is 1878 Nm

next . . . what is that in term of force?

Force = Torque / radius

so

1878 Nm / .33m (approximate wheel radius in meters) = 5690 N

next acceleration = Force / mass (this is really the meat of what we want)

5690 N / 1360 kg = 4.18 ms/s

Taaaa Daaaa 3rd gear acceleration at 5000 RPM approximated. Now let's look at 4th gear . . . .

333 Nm (engine torque) x 1.13 (4th gear ratio) x 4 (diff ratio) = 1505 Nm
1505 Nm (torque at the wheel) / .33m (tire radius) = 4561 N
4561 N (force at the wheels) / 1360 kg (car's mass) = 3.35 ms/s


So . . . .

3rd gear accelerates the car at 4.18 ms/s and 4th gear accelerates the car at 3.35 ms/s at 5000 RPM.

In the range of 3000 RPM to 7400 RPM torque from the engine varies by 10%. The difference in gearing varies by almost 30%.

Bottom line: lesser gears ALWAYS accelerate faster EVEN at high RPM so stay in 3rd until the bitter end if you want max acceleration . . .

and


Horsepower is meaningless when discussing acceleration as it is a measure of Work over distance NOT FORCE.



Torque and gear ratios are all that matter for acceleration.

Thundermoose

http://www.onpointdyno.com/?p=3306

winders

Well, you are going to find that your first big splash here has you supporting a position with no scientific validity.

Look here:

http://www.onpointdyno.com/?p=3306

TXE36

Talk about asking for it. First off, I'd suggest you stay away from numbers as they don't do anything to make your point.

That's not debatable, W = F x d.

F = ma -> a = F/m. Given m is fixed, for more a, you want more F. Torque is merely a turning F, so for more a you want more T for Torque.

Horsepower is work over time -> force times distance -> torque times revolutions.

While it may first appear that all that matters for a is T, it's not that clear, as the motor has to be able to produce that T at the rate is required to turn - that's where horsepower comes in. The tire turns at the rate (tire RPM) that the torque must be delivered (wheel horsepower).

Look at it another way, if the horsepower is zero, then you have zero work over time -> zero revolutions -> zero torque.

-Mike

winders

Look here too:

http://www.competition-car-engineeri...wer_Torque.htm

Coochas

Mark? Is that you?

noturavgm

Oh man, good thing MK is on hiatus.

JP66

Actually I have this funny science called physics on my side and you are not making a single argument to refute what I am saying. The internet is rife with folks that talk about matters of which they have no clue. As a slight bravado I should mention that I am a graduate of Dartmouth College Magna Cume Laude with a BSEE.

What was your degree in?

Yes and you're saying exactly what I said but not understanding the implications.

Horsepower measures WORK.

You can not use Horsepower to calculate acceleration without first backing out FORCE. Horsepower is a reflection of the Force produced. You need the force before you can calculate the Horsepower so to try and say Horsepower matters to acceleration is simply foolish and shows an utter lack of understanding of the terms.

linzman

Wow, Kibort X 991. That's no way to keep getting feedback on your other posts.

Thundermoose

Matt Lane

I think I know your Evil Twin. I don't engage with him either.

Veloce Raptor

Horsepower sells cars.

Torque wins races.

JP66

So here's a quick brain teaser.

What if I have a tractor that produces 2000 Horsepower? Why doesn't it accelerate at crazy speeds?

Why . . .

Because Horsepower is NOT a measure of FORCE

ACCELERATION = FORCE / MASS

Horsepower measures POWER

POWER = (F x d)/ t

get it?

Acceleration is dependent on FORCE.

Horsepower is a measure of FORCE over time and distance.

Yes, they are closely related but when calculating acceleration it is ONLY FORCE that matters.

JP66

LOL thanks!

I know I'm barking up a tree here. but I guess I love a good argument!

sbelles

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