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A good video on an ageless question. Peak numbers of torque and HP are helpful information. Torque and HP curves provide us more information. But, we need a good transmission to get the most out of our torque and HP.
those parameters are what engine designers work with. On top of that, they must also consider longevity and cost. And on top of that you got the weight of the vehicle and air resistance. The final evaluation of an engine and the vehicle it’s propelling will be revealed on the track.
So so how good is the HD powerplant for cruisers and baggers? Given all the weight of a Harley and it’s awesome looks and acceptable cost, I say it does pretty good.
I think as applied to an internal combustion engine, he's mostly correct if the engine were to stay running. In that case, just as your torque wrench scenario, if there is not enough torque for HP to be measured, then the engine stalls. It just won't run.
Horsepower is a fairly glamorous term for torque X RPM, and what a lot of people focus on. For our purposes, I believe that torque is the important number. Without that, we go no where!
But it is fun to say "She's makin' X amount of horsepowers on the dyno!"
First thing I look at on a dyno sheet is the torque curve. Where it comes on, and for how long and flat. That tells me how easy and fun the bike will be to ride. Then I look at HP.
This is a great bike to ride. It pulls every where.
Simply, a relation between torque and horsepower is clear. Horsepower is a relation between rpm and torque. Given a certain hp, the torque will be high when the rpm is low and reversed. Race engines like the japs have a lot of hp, but an extreme high rpm and low torque. HD and comparable engines have a low rpm and a high torque. Once I knew exactly the formula to calculate. Hp = torque x rpm / 5252
Example: an engine with 200Nm torque and 3000 rpm delivers 200x3000 /5252 = 114 hp
A high torque at a certain hp is obtained by a long stroke and a medium bore with a 'low' rpm. The mass forces of the piston and the long stroke (accumulation of power in the mass of piston and piston rod, named 'kinetic energy' of the piston and rod) limits the rpm. A low torgue and a high rpm is obtained by 'square engines" or 'short stroke' engines with a bore bigger than the stroke, which permits a higer rpm with low mass forces of the piston and rod due to the short stroke. Lower build-up of kinetic energy in the piston and rod.
Japanese and Italian high rpm engines have an extreme short stroke, multiple cylinders and a small bore, where the hp is obtained by the high rpm. HD and other 'high torque' engines are due to this kinetic energy not so quick to be accelerate in rpm as short stroke engines. They need less cylinders to obtain the same hp. They have compared to the high rpm engines a relatively high torque and relatively low rpm. Which has a big influence on the limited wear of the cylinderwalls, because the friction speed between the piston rings and cylinder wall is much lower than with high rpm engines. In most cases resulting in a longer lifetime before overhauling of the engine, depending of the lubrication.
Last edited by Bart van der Meulen; Jan 23, 2018 at 05:42 AM.
First thing I look at on a dyno sheet is the torque curve. Where it comes on, and for how long and flat. That tells me how easy and fun the bike will be to ride. Then I look at HP.
This is a great bike to ride. It pulls every where.
Agreed! Lets say you were gonna make a drag strip run with that...Looking at that curve, you could shift it anywhere between 4500 and maybe 5200 rpm and it would likely run run about the same times, depending on gearing. That would put the motor near peak torque after the shift was made. Wringin' that this out to peak horsepower (about 6000rpm) in each gear, might actually result in a slower run, although geared correctly and running it out thru the traps to the peak HP rpm would give the fastest trap speed
I used to say that torque is what makes a vehicle "**** and git" for example, my 86 5.0 Mustang will leave off from a stop quicker than a Hyandai Elantra, but the Elantra will eventually catch up and pass at highway speed. So the Fox body has torque but the Hyundai with its modern technology has it beat at horsepower. (Stock engine comparison).
From: Depends on who wants to know.........and why.
It was explained to me "Horsepower is how fast you will hit a brick wall, and torque is how far you can drag the wall after you hit it". I like the explanation in the video better.
Here is the dyno sheet on my Kawasaki ZR1200. It's the base test and then after I added pipes, pod air filters, and a rejet
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