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  #11  
Old 10th July 2007
Sleeper Sleeper is offline
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Your starts are something that will need practice. Talk to some of the guys here and at your local track about technique. It helps to see an example in person. You never want to drop the clutch, but slip it instead. With practice you'll easily be leaving the line at over 3000 rpm.
I'm still looking for that excel formula. I've applied the formula to many different applications: Jap bikes, Harleys, cars, trucks, etc., and had positive results with all. It eliminates the ifs, ands, buts, and erroneous opinions.
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  #12  
Old 10th July 2007
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This is exactly what a horsepower curve is all about. It takes into account that the rpm the motor is turning is also a component of the performance. The more rpm you're turning, the more gear reduction you can apply at a given speed, and hence the more you can multiply the motor's torque. Horsepower is a complete description of performance, torque is not.


Quote:
Originally Posted by CBAS5 View Post
If hp is a complete description of performance, then why show the torque curve? Why not just show the hp curve?
Good Question, the top paragraph is the kind of answer or statement you will get from someone that might be a good wrench or dyno operator. But it won't be the same answer you'll get from good mechanical engineer, physicist, or even a well educated and intelligent racer.
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  #13  
Old 10th July 2007
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aswracing aswracing is offline
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Quote:
Originally Posted by Sleeper View Post
Mikel NY
Running at the highest average peak torque in every gear is the short answer.
It might be a short answer, but it's a wrong answer.

Torque is twisting force, without any regard for speed. But speed is enormously important.

For example, if you have 80 ft-lbs at 3000 rpm, you can get twice as much done as if you had 80 ft-lbs at 1500 rpm. You're making the same torque, but you're making it twice as fast.

In fact, you could take that 80 ft-lbs at 3000 rpm, gear it down 2:1, and have 160ft-lbs at 1500 rpm. In other words, you have the option of making twice the torque, but doing it at the same speed as the weaker motor.

So you see, having more rpm is a huge advantage. You can make small torque into big torque if you have more rpm. That's what gear reduction is all about.

It's also exactly why a 600 race rep with 40 ft-lbs at 15,000 rpm will beat up on a Sportster making 80 ft-lbs at 5000 rpm. It may only have half the torque, but it's turning three times the rpm. So for any given rear wheel speed, it can have three times the gear reduction through the primary & tranny & final drive, which multiplies it's torque three additional times over that of the Sportster. Hence more torque reaches the rear wheel at any given rear wheel speed. Three times 40 is 120, and that's more than the 80 that the Sportster has.

That's exactly why you talk horsepower when you're talking about performance. Horsepower is literally torque times rpm. It combines the twisting force (torque) with the speed of twisting (rpm). Both are equally important when you're talking about performance. They're also totally interchangeable. Gear something down, you decrease rpm and increase torque. Gear something up, you increase rpm and decrease torque.

More in-depth explanation here:

http://www.nrhsperformance.com/tech_power.shtml

And in case you're wondering, yes, I am an engineer. But this is really basic physics, you don't need an engineering degree to grasp this.
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  #14  
Old 10th July 2007
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Quote:
Originally Posted by aswracing View Post
It's also exactly why a 600 race rep with 40 ft-lbs at 15,000 rpm will beat up on a Sportster making 80 ft-lbs at 5000 rpm. It may only have half the torque, but it's turning three times the rpm. So for any given rear wheel speed, it can have three times the gear reduction through the primary & tranny & final drive, which multiplies it's torque three additional times over that of the Sportster. Hence more torque reaches the rear wheel at any given rear wheel speed. Three times 40 is 120, and that's more than the 80 that the Sportster has.
All you need to say right there.

To quote something I read somewhere else, that's what puts billy biker on the trailer and ricky ricer on the podium.


THIS NEEDS TO BE MADE A STICKY SOMEWHERE!!!
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  #15  
Old 10th July 2007
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Quote:
Originally Posted by blakjak View Post
All you need to say right there.

To quote something I read somewhere else, that's what puts billy biker on the trailer and ricky ricer on the podium.


THIS NEEDS TO BE MADE A STICKY SOMEWHERE!!!
Apples to Oranges though.

Comparing an air-cooled OHV engine to a liquid cooled DOHC is like comparing Oscar de La Hoya to Mike Tyson. Sure they're both awesome in their own way... Different styles
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  #16  
Old 10th July 2007
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Quote:
Originally Posted by CBAS5 View Post
If hp is a complete description of performance, then why show the torque curve? Why not just show the hp curve?
We are all very visual and like that...just saves the math really.
I once had a tq run over rpm and a hp run over mph....that was not fun to overlay....
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  #17  
Old 11th July 2007
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Quote:
Originally Posted by Sleeper View Post
edited for name calling -raysheen
At first I thought this was a slam, but no it's a joke, no it is a slam, if I understand your point. Is that really called for? GEESH ...
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  #18  
Old 11th July 2007
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Quote:
Originally Posted by CBAS5 View Post
If hp is a complete description of performance, then why show the torque curve? Why not just show the hp curve?

Just showing the torque curve is really all that is necessary. Horsepower is nothing more than a mathematical calculation based on torque and time.
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Old 11th July 2007
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I don't have a clue what Sleeper's post 17 is tring to say!! I can't understand why you would post such a slam ( if it is a slam? )


So back to learning when to Shift.... By making the intake track longer one can move the TQ peak lower in the rpm range, so If I removed the spacer between my carb and intake tract, I would move the peak TQ up in rpms thus making more HP at higher RPMs. Is this true?
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  #20  
Old 11th July 2007
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Quote:
Originally Posted by twodownzero View Post
Just showing the torque curve is really all that is necessary. Horsepower is nothing more than a mathematical calculation based on torque and time.
At any given rear wheel speed, maximum rear wheel torque occurs at the engine's power peak, not at the engine's torque peak. That's a mathematical fact that's very easy to prove.

Let's just take a real world example.



Here's a motor we built for a guy several years ago.

The torque peak is 109.4 ft-lbs at 4600 rpm

The power peak is 117.6 hp at 6700 rpm

Pick a rear wheel speed. Let's just say 500rpm.

If we have the motor at 4600rpm, and we're in a gear that gives us 500rpm rear wheel speed, that means we have 9.2 of overall gear reduction, right? 4600 divided by 500 is 9.2.

Well, if the motor is making 109.4 ft-lbs, and you've got 9.2 of gear reduction between the crank and the rear wheel, you've got 109.4 times 9.2 equals 1006.48 ft-lbs of torque at the rear wheel. Agreed?

Okay, now let's see what happens at the power peak instead. If we have the bike at 6700rpm, and it's got 117.6 horsepower, that means it's making 92.2 ft-lbs of torque. torque = (hp times 5252) divided by rpm, if you work that out you'll get 92.2 ft-lbs, and you can see on the chart that's about right.

If we have the motor at 6700rpm, and we're in a gear that gives us 500rpm rear wheel speed, that means we have 13.4 of overall gear reduction, right? 6700 divided by 500 is 13.4.

Well, if the motor is making 92.2 ft-lbs, and you've got 13.4 of gear reduction between the crank an the rear wheel, you've got 92.2 times 13.4 equals 1235.48 ft-lbs of torque at the rear wheel. Agreed?

1235.48 is more than 1006.48. The power peak wins.

So as you can see, at the same rear wheel speed, you put more torque to the rear wheel when the motor is at the horsepower peak, not when the motor is at the torque peak.

This is exactly why horsepower is the meaningful number. It takes the engine's rpm into consideration. The engine's rpm is every bit as important as the engine's torque, because the more engine rpm we have, the more gear reduction we can apply for a given rear wheel speed. And the more gear reduction we can apply, the more we multiply the engine's torque. The important thing isn't how much torque the engine can make, or how much rpm it can turn, the important thing is how much of both it can do at once. That number is called "horsepower".

ps: there's a much more direct way to do that calculation, I did it the long way just to illustrate the concept. But the short way is just to calculate rear wheel torque directly, knowing rear wheel rpm and rear wheel horsepower. Remember, any time you know any two of the three components (torque, rpm, or power), you can can calculate the third.

Last edited by aswracing; 11th July 2007 at 05:20..
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