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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? :dunno: Any gearheads out there?
 

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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.

:2cents:
 

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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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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.

Later,
Eric
 

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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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Is this Horsepower or Torque? :D
 

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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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YellowMaranello said:
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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spicersh said:
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. :)
See my first post on this thread for a decent disagreement.

The size of the combustion chamber is irrelevant because the 4 cylinder will have twice as many 1/2 sized explosions per revolution; releasing the same amount of energy, in theory.

The 4 cylinder bike has less stroke per cylinder than a same displacment 2 cylinder bike. This shorter stroke allows the engine to rev higher which allows it to make more HP. The key to going fast is solely horsepower (and if you know the HP and the RPM you can easily calculate the torque so don't think of HP as imaginary, it's not). Torque peaks don't mean much in the real world because gearing (torque multiplication) can easily make the rear wheel torque as high as it needs to be for adequate thrust. My Bandit 400, for example, only makes 20 ft/lbs of torque. The Bandit will spank a Harley which makes 3 or 4 times the torque yet only weighs twice as much because the Bandit has nearly the same HP with half weight. It's geared to make use of small amount of torque it has by multiplying it much more than the Harley. This is not a problem with a red line of 13,000 RPM.

Big torque at low RPM is never a bad thing but it's not the only thing. If it were, the new Vulcan 2000 would be the quickest bike out there. It's not, a Harley V-rod spanks it with just over half the displacement and torque.
 

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Discussion Starter #12
I was very impressed with the number of informative responses to my original question, so I've decided to revive this thread. Main reason is that my wife's new bike is a lil' cruiser, called Savage 650, and as some may know it has a "thumper" engine, i.e single cylinder.

The bore and stroke values are identical (94 mm), which I guess means it is "squared"(?). Maximum engine speed recommendation is 6500 rpm (after the break-in period), which should supposedly top it out at 100mph. I haven't tried taking it up to 100mph, but after riding at 80mph, I'm not even sure if 100 is even attainable. I am still trying to figure out what is the deal with single cylinders and why the hell they are still made for bikes (as opposed to lawnmowers). It doesn't accelerate very well, it gets really upset and threatens suicide if you slow down too much w/o downshifting, and on top of that it backfires when you roll off the throttle or stall it. The backfire can actually be resolved by a simple carb mod, according to a Savage board.

The only advantages I have noticed so far are extremely light weight and very good fuel economy. With 50cc more displacement than my Bandit, the Savage weighs almost 100lbs less. It also gets 59 mpg, while Bandit gets only 40mpg. That fuel economy would give this bike great touring range, if the gas tank wasn't only 2.8 gal, of which .6 gal is reserve.:wtf:

What am I missing? I need someone to come to thumper's defence and explain its torque and horspower qualities as compared to other engine configurations. After all, there are some dual-sport bikes (BMW, Honda, perhaps more) that have thumpers, so there must be some good to them.

Thanks in advance for all the answers. There is a great deal of knowledge and experience possessed by the members of this board, and that's what makes it so great :thumb:
 

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This thread been dead forever, but I have to take my eyes off my drafting software so why not explain torque and horsepower to absolutely no one.

Power is work done in a period of time.
Work is Force over Distance.

Here is how this comes together.

When the spark fires it couses the piston to go down with a certain force. That force is determined by the ammount of energy released by the explosion, multiplied by the efficiency coefficien of piston engines (around 0.25 depending on RPM among other things)

Now the force travels down the connecting rod and the crank shaft turns it into Torque. In its simplest form, a crank shaft is a lever. The farthest the connecting rod is from the center of the crank the more force is generated. So for the most torque you want the crank to be very far reaching.

However, that distance is directly proportional to the stroke of the piston. And longer stroke limits your red line. (also larger bore does too, but thats for some other time).

So generally speaking short stroke (oversquare) engines will generate less torque then long stroke (undersquare) engines.

Now remember that engines produce different torque at different RPM. This is largely a product of valve overlap, intake size and exhaust back pressure. In a very generalized basis, larger intake and exhaust will allow high torque at high rpm but will limit torque at low speeds. The reason for this is inertia. In order for approximatly the same amount of air to travel down a smaller tube it must move much faster. Since its moving faster it has more momentum, and thus will continue to fill the cylinder even thou the piston is starting to come up, so long as the intake valve stays open. Of course if the tube gets too small it simply wont allow enough air to travel down it. So the engine is tuned, so that a 250cc cylinder actually inhales 280cc of air at the proper engine speed, but it inhales 200cc at the "wrong" speed.

Now since longer stroke engines cant spin as fast, they are tuned so that their best torque is at lower rpm then the short stroke engines.

This is where we get to power. Power is a multiplication of torque (force) by RPM (frequency). (RPM=1/cycle time, but thats not really important). What is important is that power gets you moving and keeps you moving. Everything we care about (acceleration, top speed) involves time as a factor. IF TIME IS A FACTOR THEN POWER IS WHAT YOU NEED.

As i said power is torque at a particular rpm times the rpm. What that means is that at low RPM the power output is heavily dependant on torque. The more torque the better. At high RPM torque can be much lower since it is multiplied by such a high RPM. This is why some engines are reffered to as torquey. Its not entirely accurate. what people really mean is that some engines make more power down low, while some engines make more power up at the top.

If you think of available power as something you harvest, then there is more of it available up top, due to the large rpm multiplication. However its less accessable there, becouse you have to wind the crap out of your engine.

Hope that helps someone.
 

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The numbers/slightly more understandable version of what Vash explained is simply this.

Torque and Horsepower are DIRECTLY related to eachother. You can calculate horsepower with torque, and vice versa.

First, we'll call 5252RPMs the Magic number, because at 5252rpms, torque=horsepower. (any valid dyno reading will demonstrate this fact by showing that the torque line and horsepower line cross at 5252). We use the number in calculating from one to the other.

To calculate Horsepower.
Torque*RPM/5252

To calculate Torque
Horsepower*5252/rpm

Torque is force applied. Horsepower is work done.

Torque is most felt at its peak. A few useful applications demonstrating this are as follows:

- In a car, you will "feel" the most pull at your torque peak. So if you let off the gas at your torque peak then slam the gas down, you'll feel a bigger "jolt" then you would doing the same thing at higher/lower rpms.
- On a bike, if you know where your peak torque is you'll notice its easier to do wheelies at that rpm just by "getting on" the throttle. If your bike makes peak torque at 8k RPMS, you'll be able to wheelie easier around that rpm range then say 4k rpms.
- On a bike, to get an idea where your peak torque is (if you don't know) is to just accellerate as fast as you can from a stop. Usually you'll be able to "feel" it pull harder when you get to a certain point, your peak torque is probably not far from there.

A harley will peak out MUCH lower, but the peak will be stronger. A sportbike will peak out a lot higher, but the peak will be less noticable.
 
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