ft-lb, hp...please help
Road Master
Joined: Dec 2007
Posts: 1,040
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From: USA
Guess the bigger message here is, you may want to start looking at how to customize your performance.....
Ultimate HDF Member
Joined: Dec 2009
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From: Potsdam, NY
The reciprocating weight of the flywheels, rods and pistons along with the long stroke and faster piston speeds at RPM is where the off-idle torque somes from.
The I-4's get the HP from lighter engine parts, slower piston speeds, less heat and higher RPM's...The I-4's go thru the traps with a higher speed compared to the faster 30-ft and 60-ft times by the Twins...Reaction time is also a factor.
The I-4's get the HP from lighter engine parts, slower piston speeds, less heat and higher RPM's...The I-4's go thru the traps with a higher speed compared to the faster 30-ft and 60-ft times by the Twins...Reaction time is also a factor.
Torque is a factor of displacement as long as breathing efficiency does not become a factor as it does in two valve engines operating at higher rpms. More displacement means more air/fuel mixture can fit in the cyl and the resulting explosion, which drives the engine, will be larger, which translates into more torque at a specified RPM. In idealized engines with no mechanical friction or breathing issues, twice the displacement should translate into twice the torque.
Horsepower (the work the engine can do) is what ultimately accelerates a motorcycle. Torque is what determines the HP at a specified RPM.
Last edited by fat_tony; Dec 10, 2011 at 12:11 PM.
Extreme HDF Member
Joined: Nov 2006
Posts: 13,389
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From: Windham,Maine
Your catching on.The reason why big inch motors are so popular,they make big torque because that is the nature of the beast,and why Harley Davidson V-Twins are so popular.Maybe not with the over the pond bike crowd simply because they are a different breed of cat all together.
Road Warrior
Joined: Jul 2011
Posts: 1,589
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From: USA
I'll be the black sheep in the family here--the 1982 Kawasaki KZ1100cc offered around 110 hp w/ 135 ft-lb of torque (please quit sayin lb-ft). That makes it the strongest of any engine at its time--overall--period. Many tried & failed, miserably. Something to note here--see the ft-lb it is well above the hp--slightly different than many engines? Well, if i were a gambling man I'd suppose I could take it (hp) over the torque, considering many high hp engines.
Club Member
Joined: Jul 2007
Posts: 463
Likes: 1
From: in a trailer next to a ditch in South Florida
Didn't really want to start this discussion again but torque is what you feel in the seat of your pants. You can NOT feel horsepower.
Horsepower as a unit of measure was determined by James Watt in 1782. By experimentation he determined that a horse could turn a mill wheel 144 times in an hour. Watts developed the horsepower as a unit of measure to use as a marketing tool to sell more steam engines (in a time when horses were still used to perform the majority of work).
Bottom line is - torque is directly measurable, horsepower is not. Horsepower is a mathematically determined number that represents the rate of performing work. As someone already pointed out, it is calculated based on torque. So, when you go to the dyno, the dyno is actually measuring the torque your bike produces and displays that directly. The horsepower curve is calculated by the aforementioned forumla and displayed on the graph.
Sorry, as part of my job I used to teach this crap and I sometimes tend to ramble about it.
Horsepower as a unit of measure was determined by James Watt in 1782. By experimentation he determined that a horse could turn a mill wheel 144 times in an hour. Watts developed the horsepower as a unit of measure to use as a marketing tool to sell more steam engines (in a time when horses were still used to perform the majority of work).
Bottom line is - torque is directly measurable, horsepower is not. Horsepower is a mathematically determined number that represents the rate of performing work. As someone already pointed out, it is calculated based on torque. So, when you go to the dyno, the dyno is actually measuring the torque your bike produces and displays that directly. The horsepower curve is calculated by the aforementioned forumla and displayed on the graph.
Sorry, as part of my job I used to teach this crap and I sometimes tend to ramble about it.
Road Master
Joined: Dec 2005
Posts: 1,078
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From: Hickory, NC
I hate to disagree with you but you can feel horsepower. Horsepower is nothing but a numerical representaton of force being applied over distance and time, or work being done. As soon as an engine starts turning, it is producing horsepower. A low torque, high horsepower engine will accelerate you faster than a high torque, low horsepower engine, give the weight of both vehicles is equal and the gearing allows both engines to be operated in their optimal powerbands. Thats the reason that a stage 2 100/90 torque/hp Harley cuiser won't touch a 80/140 torque/hp Kawasake 1400 Connie in the quarter. High acceleration, or work being done (horsepower), you can feel.
Oh, I just thought of an example that we use when we teach the difference between applied force and work. If you push on a wall with your arms, you can feel the force you are applying to the wall in your arms. However, the wall isn't going to move so there is no work performed. If no work is performed the only thing you can possibly feel is the force you've applied to the wall.
Last edited by FBFletch; Dec 12, 2011 at 06:42 PM.
Club Member
Joined: May 2007
Posts: 145,895
Likes: 821
From: 40 miles Northeast of Indy..
Wow,
, I just leaned the most in here dont' know chit about TQ and dont know where to look to find the answer.
TQ is when U take a pi$$ with a hard-on in the morning and Ur feet fly out backwards when U push it down....
, I just leaned the most in here dont' know chit about TQ and dont know where to look to find the answer.TQ is when U take a pi$$ with a hard-on in the morning and Ur feet fly out backwards when U push it down....
Last edited by oct1949; Dec 12, 2011 at 07:31 PM.
Ultimate HDF Member
Joined: Dec 2009
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From: Potsdam, NY
Well, your statement "Horsepower is nothing but a numerical representaton of force being applied over distance and time, or work being done" is absolutely correct, and also proves you wrong on two counts. The "force" you are referring to is rotational force or torque. That's what you feel - not horsepower. And, just as you said, horsepower is the rate at which work is done. You can NOT feel work. The only thing you can actually feel is the applied force (torque) that causes work to happen. That being said, I stand by my original statement.
Oh, I just thought of an example that we use when we teach the difference between applied force and work. If you push on a wall with your arms, you can feel the force you are applying to the wall in your arms. However, the wall isn't going to move so there is no work performed. If no work is performed the only thing you can possibly feel is the force you've applied to the wall.
Oh, I just thought of an example that we use when we teach the difference between applied force and work. If you push on a wall with your arms, you can feel the force you are applying to the wall in your arms. However, the wall isn't going to move so there is no work performed. If no work is performed the only thing you can possibly feel is the force you've applied to the wall.
HP = ( torque X RPM ) / 5252
An engine that produced huge torque, say 200ft/lbs at a max engine speed of 2000 RPM would only produce 75 peak horsepower. An engine that produced torque of 75ft/lbs at a maximum engine speed of 10000RPM would produce a peak of 142HP and be twice as powerful and a lot faster. This is why we have transmissions.
If you were forced to shift both engines at 2000RPM though it would be another matter. The first engine is generating 75HP at this speed but the second engine could be producing as little as 15HP at this speed.
Last edited by fat_tony; Dec 17, 2011 at 01:16 AM.
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Club Member
Joined: Feb 2008
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From: Norfolk, VA
The spinning mass of the engine does not factor into torque. This is because dynos measure torque over time which negates the effect of the inertia. If it did you could double the power output of an engine (remember HP is a factor of torque) just by adding a giant fly wheel.
Torque is a factor of displacement as long as breathing efficiency does not become a factor as it does in two valve engines operating at higher rpms. More displacement means more air/fuel mixture can fit in the cyl and the resulting explosion, which drives the engine, will be larger, which translates into more torque at a specified RPM. In idealized engines with no mechanical friction or breathing issues, twice the displacement should translate into twice the torque.
Horsepower (the work the engine can do) is what ultimately accelerates a motorcycle. Torque is what determines the HP at a specified RPM.
Torque is a factor of displacement as long as breathing efficiency does not become a factor as it does in two valve engines operating at higher rpms. More displacement means more air/fuel mixture can fit in the cyl and the resulting explosion, which drives the engine, will be larger, which translates into more torque at a specified RPM. In idealized engines with no mechanical friction or breathing issues, twice the displacement should translate into twice the torque.
Horsepower (the work the engine can do) is what ultimately accelerates a motorcycle. Torque is what determines the HP at a specified RPM.
