HP or TORQUE?
#11
04-16-2007, 07:50 PM
RE: HP or TORQUE?
ORIGINAL: Fred00
Yes, of course gearing is important. In these discussions one has to assume that both engines is mated with a set of gears suited for the task. That means that a Harley will never be geared the same as a high reving sport bike for a specific task. HP and torque can't be explained without understanding gearing. The whole concept is that high rpms can be used to make massive torque at the rear wheel. The rear wheel won't feel the difference between torque coming from a torquey engine and torque coming from high revs and short gears.
For example, 100 lb-ft @ 5000rpm will yield the same performance as 50 lb-ft @ 10'000rpm. Both will have the same power. The second engine will have half as long gears. This means it will put exactly the same torque to the rear wheel at all speeds (assuming the curves look similar in shape) and still maintaining the same top speed in all gears.
We could play with the thought that we had a 500 lb-ft engine in a Harley. Some would say "Great, it will out accelerate anything". Well, if those 500 lb-ft was made at a whopping 500rpm redline we would have to use extremely long gears just in order to make the bike reach 60mph. By using so long gears all usable torque will be gone before it reaches the rear wheel. The performance out of that kind of 500 lb-ft engine would actually be worse than a stock TC96. The power of that engine is also no more than 47 hp.
ORIGINAL: grunt
Actually that link is more about gearing than it is HP and torque. Low torque motors (such as the hi-revving sport bikes) MUST have lower gears (higher numerically) to compensate. Torque from an engine is constant once parasitic losses are factored in.
High HP numbers are an indication of a fast motor, but unless coupled w/proper torque (and gearing), they will lose in shorter race distances. And of course the weight ration comes into play.
But basically identically geared, similar weight objects will have different results depending on distance AND the discrepancies between their torque and HP ratings.
Actually that link is more about gearing than it is HP and torque. Low torque motors (such as the hi-revving sport bikes) MUST have lower gears (higher numerically) to compensate. Torque from an engine is constant once parasitic losses are factored in.
High HP numbers are an indication of a fast motor, but unless coupled w/proper torque (and gearing), they will lose in shorter race distances. And of course the weight ration comes into play.
But basically identically geared, similar weight objects will have different results depending on distance AND the discrepancies between their torque and HP ratings.
For example, 100 lb-ft @ 5000rpm will yield the same performance as 50 lb-ft @ 10'000rpm. Both will have the same power. The second engine will have half as long gears. This means it will put exactly the same torque to the rear wheel at all speeds (assuming the curves look similar in shape) and still maintaining the same top speed in all gears.
We could play with the thought that we had a 500 lb-ft engine in a Harley. Some would say "Great, it will out accelerate anything". Well, if those 500 lb-ft was made at a whopping 500rpm redline we would have to use extremely long gears just in order to make the bike reach 60mph. By using so long gears all usable torque will be gone before it reaches the rear wheel. The performance out of that kind of 500 lb-ft engine would actually be worse than a stock TC96. The power of that engine is also no more than 47 hp.
#12
04-16-2007, 08:00 PM
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RE: HP or TORQUE?
ORIGINAL: grunt
You are somehow imagining that you can launch anything at 10k rpm w/o something to actually hold it to the pavement. And if you honestly believe a TC96 makes only 47hp. Just dyno'd an 88 that had nothing but new exhaust. That was 75hp. No exhaust on the planet is good for a 60% increase in power.
You are somehow imagining that you can launch anything at 10k rpm w/o something to actually hold it to the pavement. And if you honestly believe a TC96 makes only 47hp. Just dyno'd an 88 that had nothing but new exhaust. That was 75hp. No exhaust on the planet is good for a 60% increase in power.
And yes, launching at 10k is quite possible. That is exactly what the supersport guys are doing at the start of every race. High torque in the low rpms is of course prefered in the starting moment, but a high rpm start on a short geared bike can be very quick indeed.
This is how it looks like if you know what you're doing:
http://www.youtube.com/watch?v=xMDV6HpADQc
#13
04-16-2007, 08:06 PM
RE: HP or TORQUE?
ORIGINAL: Fred00
The 47hp is for the imaginary 500 lb-ft engine, not the TC96. Sorry if that was unclear. It's fixed now.
And yes, launching at 10k is quite possible. That is exactly what the supersport guys are doing at the start of every race. High torque in the low rpms is of course prefered in the starting moment, but a high rpm start on a short geared bike can be very quick indeed.
ORIGINAL: grunt
You are somehow imagining that you can launch anything at 10k rpm w/o something to actually hold it to the pavement. And if you honestly believe a TC96 makes only 47hp. Just dyno'd an 88 that had nothing but new exhaust. That was 75hp. No exhaust on the planet is good for a 60% increase in power.
You are somehow imagining that you can launch anything at 10k rpm w/o something to actually hold it to the pavement. And if you honestly believe a TC96 makes only 47hp. Just dyno'd an 88 that had nothing but new exhaust. That was 75hp. No exhaust on the planet is good for a 60% increase in power.
And yes, launching at 10k is quite possible. That is exactly what the supersport guys are doing at the start of every race. High torque in the low rpms is of course prefered in the starting moment, but a high rpm start on a short geared bike can be very quick indeed.
#14
04-16-2007, 08:11 PM
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RE: HP or TORQUE?
Supersport is no "Pro Drag class". It's short-wheelbased, 600cc, crotch rocket road racing on normal road courses.
I post the video again so you don't miss it. Not an example of a supersport start, but it is still an high rpm bike launching hard. It's all about clutch and throttle control. Just beacuse it's difficult doesn't mean it's impossible. Rear-wheel torque is rear-wheel torque. It doesn't matter if it comes from high engine torque or high rpms and short gearing. The rear-wheel can't tell the difference.
Here's the vid:
http://www.youtube.com/watch?v=xMDV6HpADQc
I post the video again so you don't miss it. Not an example of a supersport start, but it is still an high rpm bike launching hard. It's all about clutch and throttle control. Just beacuse it's difficult doesn't mean it's impossible. Rear-wheel torque is rear-wheel torque. It doesn't matter if it comes from high engine torque or high rpms and short gearing. The rear-wheel can't tell the difference.
Here's the vid:
http://www.youtube.com/watch?v=xMDV6HpADQc
#15
04-16-2007, 08:19 PM
Road Warrior
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04-16-2007, 08:26 PM
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RE: HP or TORQUE?
ORIGINAL: chester1957
Torque is where it's at. Very few engines make equal HP and torque. Buicks GS was a perfect example, little over 400 HP andn over 500 ft/lbs of torque. That's what you call a tire shredder.
Torque is where it's at. Very few engines make equal HP and torque. Buicks GS was a perfect example, little over 400 HP andn over 500 ft/lbs of torque. That's what you call a tire shredder.
You can think of it this way: Would AMA let Buell compete with the XBRR if the huge torque advantage really made a difference? Of course not. The rules are there to make for good, fair racing. AMA knows full and well that the higher torque will not be an advantage on the track.
#17
04-16-2007, 11:42 PM
Road Master
RE: HP or TORQUE?
Here are a few concepts that help some better understand the relationship between HP and TQ.
HP is the measurement of work actually being or capable of being performed which iswhy some guy by the name of Newton decided we need a way to measure it.
For us, rear wheel TQ iswhat is important,in a given gear, RWTQ is peak when theengine TQ is at itspeak, but more importantly, at a givenMPH, RWTQ is peak when we select a gear that puts the engineat itspeak HP due to the fact that the transmission is a TQ multiplier.For maximum acelleration orgetting a truck to the top of a hill quicker,we who selectgears that allow the engine to average the most HP, not TQ,willget us there sooner.
For best cruising gradeability (ability to go up and down hills without shifting) select an engine/gear combo that puts your engine at its peak TQ RPM, because as stated previously, in a given gearRWTQ is peak when the engineTQ isat its peak.The lower the engine's RPM that we can accomplish this, the better thefuel MPG. If you understand all of this, now try to select a cam.
HP is the measurement of work actually being or capable of being performed which iswhy some guy by the name of Newton decided we need a way to measure it.
For us, rear wheel TQ iswhat is important,in a given gear, RWTQ is peak when theengine TQ is at itspeak, but more importantly, at a givenMPH, RWTQ is peak when we select a gear that puts the engineat itspeak HP due to the fact that the transmission is a TQ multiplier.For maximum acelleration orgetting a truck to the top of a hill quicker,we who selectgears that allow the engine to average the most HP, not TQ,willget us there sooner.
For best cruising gradeability (ability to go up and down hills without shifting) select an engine/gear combo that puts your engine at its peak TQ RPM, because as stated previously, in a given gearRWTQ is peak when the engineTQ isat its peak.The lower the engine's RPM that we can accomplish this, the better thefuel MPG. If you understand all of this, now try to select a cam.
#19
04-17-2007, 12:20 AM
RE: HP or TORQUE?
The perfect example of TQ vs HP was the biker build off of Williams vs. Compton.
One was a sportser based drag bike that was a torque monster the other was a rocket based high HP beast. The set up to do the 1/4. The high TQ bike was fast out of the hole but the high HP prevailed becuase of what was said earlier, once in higher RPM's and fast speed the HP means more than the TQ.
But for the hole shot, TQ is where it's at.
One was a sportser based drag bike that was a torque monster the other was a rocket based high HP beast. The set up to do the 1/4. The high TQ bike was fast out of the hole but the high HP prevailed becuase of what was said earlier, once in higher RPM's and fast speed the HP means more than the TQ.
But for the hole shot, TQ is where it's at.
