HP vs. TQ
Thread Starter
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Elite HDF Member
Joined: Sep 2007
Posts: 4,541
Likes: 1
From: Nuevo México, Los Estados Unidos de América
RE: HP vs. TQ
ORIGINAL: JB
HP makes you fast
TQ makes you quick
HP makes you fast
TQ makes you quick
Anyone look at that site and figure out the "power" at the rear wheel? I'm still feeling like that site is wrong, at least for a high torque low hp machine, I shift sooner at lower gears and closer to redline up high... to give me more hp up top...
Cruiser
Joined: Oct 2007
Posts: 144
Likes: 0
From: NYC
RE: HP vs. TQ
OK... back to physics class
Torque is measured in units of weight x length of lever. (a crank shaft is a type oflever)
100 ft/pounds can sit there all day long and never move... 0 HP is being developed
move it even an inch and you've started making HP (not much HP and still 100 ft/pounds of torque)
HP is work done/TIME
That is the real number you'reworking toward. Torque is simply how much force is being applied to the lever.
The trick is to balance the two numbers so that the peak HP and torqueis developed in the rpm range that is most beneficial to the application.
Now for the question... severum17 said it .... the butt dyno will tell you when to shift on the street.
If you're racing, you need to do several "test and tune" sessions to find your optimum shift points.
Torque is measured in units of weight x length of lever. (a crank shaft is a type oflever)
100 ft/pounds can sit there all day long and never move... 0 HP is being developed
move it even an inch and you've started making HP (not much HP and still 100 ft/pounds of torque)
HP is work done/TIME
That is the real number you'reworking toward. Torque is simply how much force is being applied to the lever.
The trick is to balance the two numbers so that the peak HP and torqueis developed in the rpm range that is most beneficial to the application.
Now for the question... severum17 said it .... the butt dyno will tell you when to shift on the street.
If you're racing, you need to do several "test and tune" sessions to find your optimum shift points.
Seasoned HDF Member
Joined: Jul 2007
Posts: 6,336
Likes: 67
From: SW Minnesota
RE: HP vs. TQ
http://www.revsearch.com/dynamometer...orsepower.html
Horsepower = torquexrpm / 5252
Below 5252 rpm any engine's torque number will always be higher than its horsepower number, and above 5252 rpm any engine's horsepower number will always be higher than its torque number. At 5252 rpm the horsepower and torque numbers will be exactly the same.
Your hp and torque will be equal at 5252 RPM--always. Think of torque as acceleration, and hp as speed. If you don't have enough horsepower, you won't reach maximum torque, such as driving a 10 hp 100cc cycle that won't go faster than 60 mph in high gear. Just because you have enough hp on your Harley to exceed your maximum torque doesn't necessarily make it advisable to do so routinely, especially with a push rod engine.
Also, because of the long stroke ofour V-Twins vs the multi-cylinder high revving short stroke bikes, you should utilize the torque (think of it as leverage on your crankshaft), rather than the hp. If you are not familiar with "piston speed" in relationship to the stroke ofyour engine,you should read up on that as well.
Horsepower = torquexrpm / 5252
Below 5252 rpm any engine's torque number will always be higher than its horsepower number, and above 5252 rpm any engine's horsepower number will always be higher than its torque number. At 5252 rpm the horsepower and torque numbers will be exactly the same.
Your hp and torque will be equal at 5252 RPM--always. Think of torque as acceleration, and hp as speed. If you don't have enough horsepower, you won't reach maximum torque, such as driving a 10 hp 100cc cycle that won't go faster than 60 mph in high gear. Just because you have enough hp on your Harley to exceed your maximum torque doesn't necessarily make it advisable to do so routinely, especially with a push rod engine.
Also, because of the long stroke ofour V-Twins vs the multi-cylinder high revving short stroke bikes, you should utilize the torque (think of it as leverage on your crankshaft), rather than the hp. If you are not familiar with "piston speed" in relationship to the stroke ofyour engine,you should read up on that as well.
Outstanding HDF Member
Joined: Mar 2005
Posts: 2,913
Likes: 8
From: Darlington WI.
RE: HP vs. TQ
It pretty much comes down to if you're running high speedhard and flat out you're going to be running at a higher RPM and will running the HP curve. Which means stirring the gear box a lot to keep RPM upat the peak of the curve, this is done to help maintain power and speed while running through corners. For just about all you're normal riding were you're speeds are going to varying and youdon't have worry about maintaining the highest possible speed then you would be running the TQ curve. The more over lap youhave between the two curves the better off you are for normal riding. I don't know if that helps or not, I'm not real good at explaining things.
Road Captain
Joined: Oct 2007
Posts: 515
Likes: 0
From: The Woodlands, TX
RE: HP vs. TQ
I'm going to ask the question because the answer is going to differ based on your response. What are you trying to do? Develope shifts points for drag racing or daily driving? If you want a bike that feels fast on the street (stop light to stop light) you need to develop an engine that produces it max torque at low rpms. If you want a racing engine it will develope all of its power (HP) in the higher rpms. Like a previous poster wrote, you will have to do some test/tune sessions at the track to determine your best shifts points. Just because your engine produces it's max HP at 6500 rpmsdoesn't mean you shift at that point. More than likely it will be beyond that so that when you upshift you do not go too far out of that max HP rpm range...
Thread Starter
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Elite HDF Member
Joined: Sep 2007
Posts: 4,541
Likes: 1
From: Nuevo México, Los Estados Unidos de América
RE: HP vs. TQ
ORIGINAL: txoval
I'm going to ask the question because the answer is going to differ based on your response. What are you trying to do? Develope shifts points for drag racing or daily driving? If you want a bike that feels fast on the street (stop light to stop light) you need to develop an engine that produces it max torque at low rpms. If you want a racing engine it will develope all of its power (HP) in the higher rpms. Like a previous poster wrote, you will have to do some test/tune sessions at the track to determine your best shifts points. Just because your engine produces it's max HP at 6500 rpmsdoesn't mean you shift at that point. More than likely it will be beyond that so that when you upshift you do not go too far out of that max HP rpm range...
I'm going to ask the question because the answer is going to differ based on your response. What are you trying to do? Develope shifts points for drag racing or daily driving? If you want a bike that feels fast on the street (stop light to stop light) you need to develop an engine that produces it max torque at low rpms. If you want a racing engine it will develope all of its power (HP) in the higher rpms. Like a previous poster wrote, you will have to do some test/tune sessions at the track to determine your best shifts points. Just because your engine produces it's max HP at 6500 rpmsdoesn't mean you shift at that point. More than likely it will be beyond that so that when you upshift you do not go too far out of that max HP rpm range...
But I do want to get the most out of it. When I "build" my engine it will be for low-end... but right now I'm just trying to findout my how I even use the info I have to figure ideal shift points.
Sounds like given that my engine will never be running around 6k (I hope), the TQ numbers matter. Still, the "Power" band is different from gear to gear. Or at least feels like it is.
Just trying to get the most out of the bike I have.
Road Captain
Joined: Oct 2007
Posts: 515
Likes: 0
From: The Woodlands, TX
RE: HP vs. TQ
I don't think there is an equation that is going to tell you when to shift. You will have to run the bike at the track using different shift points to get you best time. Start with you max HP rpm and work each way to see what best for you
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Joe Kucinski
Grand HDF Member
Joined: May 2007
Posts: 3,870
Likes: 499
From: Alberta
RE: HP vs. TQ
Here is my dyno. Note that I have 100ft lbs from 2200rpm (Thankyou HQ). When I ride, I normally keep it between 2000 - 4500rpm. After a while you can "feel" it...but when I want some metric cruiser for dessert, it's shifted as it hits6000. From a first gear WOT run, the front wheel will "float" about 6-8 inches thru second then pop up again in third and settle down by the time I grab fourth...all quite quickly. (It don't spend any time in first...) See how that relates to the power curve; or rather, plateau.....
[IMG]local://upfiles/32069/A13065F31C334C19A17B125AF144A17D.jpg[/IMG]
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[IMG]local://upfiles/32069/A13065F31C334C19A17B125AF144A17D.jpg[/IMG]
[IMG]local://upfiles/32069/635043C600294724A92737A8466EE504.jpg[/IMG]
Road Captain
Joined: Nov 2005
Posts: 711
Likes: 0
From: Bothell, WA
RE: HP vs. TQ
On a flat level road, use your torque to move you along and don't worry about where you shift, as long as you don't shift so soon that you LUG the engine. Use your horsepower "sweet spot" when you got the ol'lady on the back, are fully loaded with your gear, and are pulling a mountain pass. In other words, TQ is for speed, HP is for power. You only need to run the bike up to its peak HP when your loaded down or pulling a hill/mountain at speed. Of course when you are talking about "top end", you have to use HP due to wind drag and frictional forces, but since an HD is not a high HP streamlined racing machine with a high revving engine to begin with, who gives a crap? It's like asking where the "sweet spot" is on an M1 TANK! If you want to go FAST, buy a Ducatti!