Horsepower vs. torque (not the movie!) - Sportbike Forum: Sportbike Motorcycle Forums
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post #1 of 14 (permalink) Old 01-30-2004, 11:50 PM Thread Starter
 
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Question Horsepower vs. torque (not the movie!)

This question has been bugging me for a while. In MC reviews I always see HP and torque specs mentioned, often pointing out that V engines are "torquey", while i-4 get more HP at their peaks. I have a vague understanding of what torque is about, i.e. lower gears have more of it, and higher gears have less, due to the different ratios/distance from the source of power (engine) and where that power is applied (tire on the pavement). I have not ridden anything other than my Bandit 600 (i-4) and briefly Rebel 250, so I wonder in what ways one feels the "torqueiness" of V-twin bike. What is it about the V-twins/quads that gives them better torque specs? Any gearheads out there?
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post #2 of 14 (permalink) Old 01-31-2004, 09:26 AM
 
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when twins are called torqey, they mean they make good power at lower revs and therefore are fairly user friendly requiring less shifting to stay in the power. horse power is a function of engine speed so the faster the engine spins the more power it makes. a 4cyl 1000 cc bike can spin much faster than a 2cyl 1000 because the stroke is much shorter. stroke determines the speed a piston must travel at and piston speeds can't exceed 4-5k feet/sec or some such unit of measure. blah blah blah, a 4 cyl bike makes more power at a higher possible rpm compared to a 2 cyl bike of the same displacement. whatever power the twin does make though it will make at a much lower rpm which means you don't have to rev the piss out of it to get to the power in the first place.

I personally prefer i-4s but have nothing against twins.

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post #3 of 14 (permalink) Old 01-31-2004, 01:04 PM
 
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Very well answered above. The larger pistons & longer stroke of the V-twin means the bob-weight or crank is heavier & so lots of torque at lower revs. One will never see a V-twin climbing up to 10,000 before shifting into a higher gear or possibly "coming on pipe" (where the engine really starts to sing & punch out revs) though this is common with fours of sportbikes.

Engines are designed to do different things like a one-lunger (single) dual OHC of a "works" road racing bike back in '50 could climb to 7,250 rmp as its red line & when the7 broadened the piston & shortened the stroke (actually over squared it ) that same engine could sing up to 7,500rmp. My how times have changed as no one would have dreamed a bike sold to the publiC could rev up to 14 to 18 thou & punch out to 180hp.
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post #4 of 14 (permalink) Old 02-02-2004, 04:44 AM
 
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Here's a good way to relate to torque and horsepower.

when you were a little kid and had your BMX bike. Torque was the way you could stand up on the pedals and pull the easiest wheelies you ever saw.

Horsepower was when you got on your ten speed and hit a long, flat straight and you could have gone 60 mph if only you could have turned those pedals faster and faster and faster.

I've had quite a few inline fours, but I don't know if I'll ever go back after having a twin. Now I just want a bigger twin, maybe a superhawk or older TL1000.

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post #5 of 14 (permalink) Old 02-02-2004, 07:57 AM
 
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V-Twins and IL4s of equal displacement quite likely make similar peak torque numbers, it's just that V-twins usually make the torque peak at a lower RPM.

It's not because V-twins are inherently "torquier", it just that they can't rev as high so the valves, intake intake and exhaust tracts/ports, carbs or TBs, air box and exhaust systems are designed to produce peak torque at a lower RPM.

The only reason V-twins are (were???) popular as sport bikes was the WSB and AMA Superbike rules that allowed a 250 cc advantage for twins. Manufactures marketed them well in order to ensure they could race them (both world and AMA superbike series requred that the bikes be based on street bikes with a minimum sales requirement). With 250cc advantage rules gone, you'll see fewer and fewer V-twin sport bikes. I'd be shocked if the next generation, top dog, Ducati street sport bike was not a V4.

In the real world, an IL4 of equal displacement has a big advantage over a V-twin becuase it weighs less and makes more power. The torque produced by the Yamaha R1 and Suzuki GSXR1000 at low to mid revs is breathtaking and the top end rush is way beyond any stock V-twin.

That said, I like to ride twins for the feel and the sounds, but not enough to buy one.
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post #6 of 14 (permalink) Old 02-12-2004, 08:00 AM
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Is this Horsepower or Torque?
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post #7 of 14 (permalink) Old 02-12-2004, 06:19 PM
 
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Simplest way I've ever heard it explained....


Horsepower is how fast you can go, and torque is how fast you get there.
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post #8 of 14 (permalink) Old 02-13-2004, 07:58 AM
 
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Quote:
Originally posted by Jester
Is this Horsepower or Torque?
No that's elasticity and photoshop
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post #9 of 14 (permalink) Old 02-13-2004, 08:31 AM
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The seat of the pants difference while riding is very evident at lower to mid RPM's as encountered most often in street riding. The twins with all of their down low grunt (torque) will pull nicely at those lower revs. When you're running either one in the power band, near redline, the difference in feel is largely diminished. Then it's horsepower, regardless of how it came to be, torque or revs.

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post #10 of 14 (permalink) Old 02-13-2004, 08:44 AM
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Quote:
Originally posted by YellowMaranello
Simplest way I've ever heard it explained....


Horsepower is how fast you can go, and torque is how fast you get there.
That sounds like "top speed" and "acceleration" to me, not horsepower and torque. I could be wrong though.

The best way I've heard it explained is that torque is what moves you down the road, with horsepower simply being a byproduct. Torque is what is actually measurable, while hp is calculated based on your torque (among other things).

As far as what gives them better torque specs, take two engines of the same displacement, one an I4 and one a twin. If they have the same displacement, then the combustion chamber of the twin is bigger (two less cylinders), therefore causing a bigger explosion, meaning more energy is released per cycle to turn the crank. That bigger blast of energy is converted to more torque, which is the measurable part. The rpms are then used with the torque measurement to calculate the hp.

Hopefully I got that all right. I'm sure someone will correct me if I didn't.

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