Horsepower, what is it?

"Gear bound". Is it possible to get a definition for that term?
Gear bound likely has no technical definition.
It is a term used by mostly oval racers to describe a condition as shown above.

My belief is this is caused by our single circuit carburetors providing excess fuel when demand for torque drops off.
Automotive carburetors have a power enrichment circuit which supplies more fuel as indicated by vacuum in the intake system.
When vacuum drops below a predetermined level, the system shuts off the fuel flow from this circuit, leaning out the mixture, allowing for continued acceleration.

Our system only allows for a single circuit, (the idle circuit also flows during the entire time the main circuit is flowing, effectively making it a single circuit), so no top end leaning out is available.
As the load demands drop, the system becomes too rich, dropping available torque even further. The engine simply ceases to accelerate the kart.

There are 2 solutions to this problem.
Lean the entire system, compromising low end torque, (which got you to where you are now), or increase torque demand, (add more load through a gearing change.)
While we may be able to overcome torque loss with more rpm, other factors in the engine limit rpm potential. Air flow limitations, and valve train control are a couple.
 
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The above explains why engine dyno tuning may not necessarily be reflected in on track performance.

Steady state dynos do not show this drop in acceleration due to loss of load.
Also engine does not experience as much excess rich as load stays steady.

Then tuning is a compromise between best midrange numbers (best torque) and best top end numbers (best horsepower).
Of course, using available jet sizes, tuning tools.
 
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simple example, you are going down straight and you have reached the limit of gaining acceleration because the engine is past it operating range and you need more speed. But engine just won't develop more at that rpm. Need larger driver or smaller axle gear.
Or you are geared so high that when you come out of the turn and start down the chute, you are below max torque and lose a lot of forward exceleration. Need smaller driver or larger axle gear.
Remember that is simple answer. not technical one.
This is good.

To understand requires an understanding of the torque and horsepower curve of your engine.
Peak torque is the maximum resistance the engine can overcome. The rpm this occurs at is peak torque rpm. Any rpm above, or below this rpm can only overcome less resistance.
Peak horsepower is the maximum amount of work the engine can do.
Since a component of the horsepower formula is rpm, the rpm this occurs at is peak horsepower. Any rpm above or below this rpm produces less "work".
Attempting to get more work by increasing rpm above peak horsepower rpm is, by definition, impossible.
 
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Since torque is the other variable component of horsepower, it must also drop after peak horsepower, by definition, more than the increase in rpm increases the potential for work.
 
Attempting to get more work by increasing rpm above peak horsepower rpm is, by definition, impossible.
You may have never seen the RPM/HP curve for a 2 cycle. For instance, a KT100 will (with a pipe) typically reach peak torque at about 10,300. Typically it will reach peak HP at about 11,300. Some KT100's will easily reach 15,000 RPM. Some a little more. That's with a clutch! With direct drive, I hear 17,000 RPM is not unheard of! If you can believe Pete Mueller, which I'm pretty sure you can!
 
You may have never seen the RPM/HP curve for a 2 cycle. For instance, a KT100 will (with a pipe) typically reach peak torque at about 10,300. Typically it will reach peak HP at about 11,300. Some KT100's will easily reach 15,000 RPM. Some a little more. That's with a clutch! With direct drive, I hear 17,000 RPM is not unheard of! If you can believe Pete Mueller, which I'm pretty sure you can!
Yes, but are you doing more "work" above peak horsepower rpm.?
 
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I would say it is, the kart is accelerating. The force available seems to exceed the force required.
Yes, you are still doing some work, even when the kart stops accelerating, and is simply maintaining speed.
Now, the force required is called...
Torque.
In your scenario, the need and the ability to keep accelerating is the reason for your gearing choice.

In a momentum situation, wouldn't you want to be nearer to peak horsepower for the maximum amount of time?
 
In a momentum situation, wouldn't you want to be nearer to peak horsepower for the maximum amount of time?
The ideal situation would be to have an infinitely variable ratio transmission so you could keep the engine at peak torque as you accelerated. The old Buick automatic transmission was, in some ways, like that. I'm familiar with the 1955 model.

With the KT100, that's not possible, so we go something like 3000 RPM over the peak, and more. Past the peak, there's still more than enough HP to keep accelerating. Remember, torque is the measure of work, HP is how much work. A simplification I know.
 
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Horsepower is measure of actual work being produced at an instantaneous moment. It doesn't indicate anything about potential for jerk. Observing the curve gives some clues about potential on either side of the moment, however.

Gear bound seems like a useless term to me. I'd prefer the simpler "incorrect ratio." I'm not even sure there's agreement on what "gear bound" means on this board. In a technical sense, gear bound to me would mean that point where the engine's available torque cannot overcome the mechanical resistance of the system, and therefore cannot keep accelerating. I think it gets used here to denote a situation where the torque curve has fallen off so dramatically that even though the kart is still accelerating, you're getting passed by your more correctly geared competitors. It's a basic failure to analyze where your engine's peak area under the curve is, and gearing to stay in that zone. Some racetracks have such a long acceleration zone that it's impossible (based on geometric realities of the axle, tire, and speed) to stay in that zone. In such cases you must decide to compromise acceleration rate or final speed (gear bound.) At no point does the acceleration really stop, you're just operating in a less efficient zone of the engine's power. It's the upper rpm equivalent of what happens when you start from a standstill with a low-engagement clutch -- the engine "chugs" a while until it reaches a more optimal power band, then seems to "take off", and then, ultimately, "falls off again." That middle sweet spot is what you try to gear for, favoring maximum acceleration (increasing rate of work being done.) All of racing is about efficiency. You rely on the builder to get you the most power from efficient intake and combustion. You select gearing to stay in the sweetest spot of that power being produced, and you buy ceramic bearings and drive smoothly to ensure you're not burning off that power in wasted heat (friction) energy.

Horsepower, as a definition, is pretty straightforward. Manipulating the external conditions to make best use of the rate of change in horsepower is what matters for racing. 2 stroke superbikes made brutal horsepower....but were equally brutal to drive and had 6 or 7 speed gearboxes to keep the bike operating in that 1200 rpm band of brutality.

Part of this, as relates to karting, is why I DETEST flat footed follow-the-leader dirt oval karting. It's a great exercise in efficiency.....until you get slammed out of place and freight-trained because that's the only way to jockey for position when all the karts and tracks are set up so that there's only .001s difference in rates of work being done. Formula 1 is at the opposite end of the problem, where the limitations of mere humans are encountered, and for the HP and braking HP, the humans simply can't operate with precision within .0001s and things are happening so quickly that 20' of braking needed to pass can't be achieved because the tires are still adhered at the limits of human reaction times...

I digress, but my point is that race engineering is an elegant mix of tradeoffs, and the winner is the one who manages the correct tradeoffs.
 
[QUOTE="alvin l nunley, post: 820051, member: 2695"
With the KT100, that's not possible, so we go something like 3000 RPM over the peak, and more. Past the peak, there's still more than enough HP to keep accelerating.
[/QUOTE]

Herein lies an inherent problem in methodology when answering gearing questions on this forum.

Most gearing questions on this forum are asked in relation to 4 cycle industrial engines with limitations intended to keep them in somewhat stock form.
These engines are limited in rpm by mechanical means, such as the governor with a fixed max rpm, or by durability of components, or the components ability to control their intended mechanism. Or simply by limitation of airflow.
As such, we need to get the maximum work over time, which means running rpms very near the mechanical limits imposed by the rules. This means there is only a small window for over rev beyond peak horsepower before torque drops dramatically.
Most, if not all, oval kart races are won by momentum.
Being able to stay in the small window of peak horsepower gives the best opportunity to maintain max momentum.
 
Being able to stay in the small window of peak horsepower gives the best opportunity to maintain max momentum.

Given that most RPM drops are somewhere around 400 rpm from what I've seen on here, I'd be gearing so that my peak torque was in the range where that occurred... so I'd set my gearing so that my engine just ran out of steam where I burped it for the turn, and probably take 1 tooth off so that I stayed as short a gear as I could but didn't give up too much on restarts....
 
Actually, in the imaginary world of a lossless, infinitely variable transmission, you would want to keep the engine at peak *horsepower*, not at peak torque.

PM
you easy as
With the engine at peak torque, that would mean a transferring of that torque to the axle, wouldn't that mean you would have peak HP "at" the axle? Regardless of the RPM of the axle.

Think of a hypothetical engine with a perfectly flat torque curve, the more RPM it turns, the more horsepower that can be calculated. Same thing with the axle.

Déjà vu. I remember this discussion from somewhere else. lol
 
I believe people, mistakenly, have the idea that horsepower is an actual force of some kind, it's not, it's a calculation. How much "force" (torque) in a given amount of "time" (RPM). Raise 550 lbs. 1 ft (pronounced pounds/feet) in 1 second and you're "calculated" to be working at the "rate" of 1 HP.
Look up James Watt/HP on Wikipedia to read the whole story.
For a definition of "work", go to Wikipedia.
 
Actually, in the imaginary world of a lossless, infinitely variable transmission, you would want to keep the engine at peak *horsepower*, not at peak torque.

PM
The jr dragster people do an amazing job of using a variation of this concept for repeatable performance all day long.

The object being to get to top speed as quickly as possible, then, at the very least, maintain it, or accelerate further with over rev, if possible.
 
With the engine at peak torque, that would mean a transferring of that torque to the axle, wouldn't that mean you would have peak HP "at" the axle? Regardless of the RPM of the axle.

No... it does not.

Remember, you said: "infinitely variable transmission".

If I run the engine at peak HP (which is at a higher rpm then peak torque), the infinitely variable transmission is running a slightly lower gear ratio to be at the same axle rpm than if the engine was at peak torque. The end result, will be *more* torque (force) at the axle (contact patch of the tire) than if the engine is at peak torque and geared to the same axle speed.

The most "work" will be done with the engine at peak horsepower, period. If you have higher horsepower at the engine, you will have higher horsepower at the axle. The gear ratio takes care of how you want to "convert" that horsepower to a force vs. rpm value. We don't have zero-loss infinitely variable transmissions, so this is just an exercise in mathematics (actually: arithmetic).

But by the very formula always being quoted for calculating horsepower, this should be apparent.

Peak torque is just a force number -- it does not (nor will it ever) define how much work can be done. Work (like accelerating a kart, pushing that kart against frictional and wind resistance, etc.) requires a function of time. We have to know at what *rate* we are producing torque to have any idea what is going on.

PM
 
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you easy as
With the engine at peak torque, that would mean a transferring of that torque to the axle, wouldn't that mean you would have peak HP "at" the axle? Regardless of the RPM of the axle.

Think of a hypothetical engine with a perfectly flat torque curve, the more RPM it turns, the more horsepower that can be calculated. Same thing with the axle.

Déjà vu. I remember this discussion from somewhere else. lol
This can be reverse engineered to find the correct answer.
Pick an axle speed.
Use peak torque rpm to calculate ratio.
Calculate the torque transferred to the axle.
Do the same for peak horsepower.

Whichever has the highest transferred torque will provide best acceleration.
 
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