some 09 stuff from yami site KINDA

[QCRider]

I was hoping that you would say "the torque on the clutch will be exactly the same, now i understand. And of course there won't be a difference in acceleration between a 120hp@8500 rpm and a 120hp@12000 rpm engine, all else being equal"

I won't say that because they wouldn't be the same. Use the Apex and Vector as an example. Max Torque on the Apex at the clutch as measured by Freddie Klies (aka Supertuner was just over 78 Lb-Ft) I have not been able to find a Dyno Chart with Max Torque numbers on the Vector, however I can say that at 7200 RPM it is around 84 Lb-Ft. I think the peak is closer to 90 Lb-Ft at a bit lower RPM, but again I can't find it. Now bump the displacement on the 120 to get to 170 and you would have some huge Torque Number. Even if you take the torque number at 170 hp and 8500 RPM it would be around 105 Lb-Ft with a peak likely over 120 Lb-Ft around 7000 RPM.

Here is Freddie's post on the Apex for those who doubt the numbers. Note that somewhere down the page he does say that these numbers were taken from the PTO, NOT the crankshaft, so the torque multiplication effect of the reduction gears is in the measured number.

http://www.ty4stroke.com/viewtopic.php?t=24185&highlight=dyno

 

[Laban]

Can we agree on the fact the no matter how you change your gearing(up/down) , the hp will stay the same but the torque will change ?

I hope that we can cause you cannot magically gain or loose hp (disregarding the frictional losses here) by changing the gearing. The formula to calculate HP is:

HP=TORQUE * RPM / 5252

So, both engines have a 120 hp output. Or input to the clutch in this case.
The hp are the same and the rpm are the same because of the gear reduction. The formula to calculate torque will then be:

TORQUE = HP / (RPM / 5252)

Only one variable left, so the result has to be exactly the same hasn't it ? Or on this case:

TORQUE = 120 / (8500 / 5252) = ~74 lbs on the clutch

And the torque from the 12000 rpm engine:

120 / (12000 / 5252) = ~52.6

What about the frictional losses ? I'd say that they're so small that we can ignore them, and also offset by the fact that the engine is much lighter.

 

[QCRider]

Did you not just prove my point? The engine that makes it's power at lower RPM will have more torque available at the clutch.

 

[Alatalo]

Hmm, I think I am with Laban, AndersY and Tork on this one...

Something that is not related to time can not be the decider of the performance of a vehicle. Torque is not related to time. Torque is just a product of force and leverage arm, also known as energy or work.
To get a true decider of performance you need to include time. Horsepower is related to time. Horsepower is torque (or energy or work) per time unit.

Because of this I would say that torque means nothing. Nothing at all, except for possibly one point in time; the non-measurable split-of-a-second when your vehicle starts to move from an absolute stand still. After this point in time it is all about horsepower - no matter if you are discussing acceleration or top speed.

If the choice is a multi-cylinder, high-rpm, smaller cc engine vs. a few-cylinder, low-rpm, bigger cc engine, I would pick the multi-cylinder, high-rpm, small cc thing any day (assuming same horsepower and primary gear in the high rpm case). Though, my reasons have got very little to do with the torque vs. horsepower discussion...

 

[QCRider]

Hold out your arm and I will twist it while and apply 10 lb-ft of Torque to it. Then I will do it again with 100 lb-ft of torque. Tell me which one makes your arm move more and faster...

 

[QCRider]

If the choice is a multi-cylinder, high-rpm, smaller cc engine vs. a few-cylinder, low-rpm, bigger cc engine, I would pick the multi-cylinder, high-rpm, small cc thing any day (assuming same horsepower and primary gear in the high rpm case). Though, my reasons have got very little to do with the torque vs. horsepower discussion...

I think this is basically the same for most of the people who prefer the 4 cylinder motor. It sounds cool.

 

[QCRider]

Hmm, I think I am with Laban, AndersY and Tork on this one...

I think that the Europeans in this list need to take a 1/4 mile ride in an American V8 powered Muscle Car. There is no high revving small displacement motor that will ever measure up to that standard.

 

[SLEDSTART]

Not without a turbo.... =)

 

[Laban]

Did you not just prove my point? The engine that makes it's power at lower RPM will have more torque available at the clutch.

No, i proved exactly the opposite. The 12000 rpm engine will of course make 74 lbs at the clutch since the hp is the same and rpm at the clutch are the same because of the gear reduction. Again, hp always stays the same, torque is changed.

I added the torque at the engine just for good measure, and that will of course be lower for the 12000 rpm engine. So ~52.6 lbs@12000 rpm at the engine will be converted to 74 lbs@8500rpm at the clutch.

I think that the Europeans in this list need to take a 1/4 mile ride in an American V8 powered Muscle Car. There is no high revving small displacement motor that will ever measure up to that standard.

Cars doesn't have much in common with snowmobiles, and cars have regular gearboxes too which make things very different. You're also thinking about this the wrong way imo, it's a compromise between more power at the low-end vs a lighter engine. And imo, when it comes to snowmobiles, a lighter engine is preferable. Especially since there's a CVT on a snowmobile.

Because of this I would say that torque means nothing. Nothing at all, except for possibly one point in time; the non-measurable split-of-a-second when your vehicle starts to move from an absolute stand still. After this point in time it is all about horsepower - no matter if you are discussing acceleration or top speed.

Exactly. This might perhaps explain a thing or two:

http://vettenet.org/torquehp.html

For an extreme example of this, I'll leave carland for a moment, and describe a waterwheel I got to watch awhile ago. This was a pretty massive wheel (built a couple of hundred years ago), rotating lazily on a shaft which was connected to the works inside a flour mill. Working some things out from what the people in the mill said, I was able to determine that the wheel typically generated about 2600(!) foot pounds of torque. I had clocked its speed, and determined that it was rotating at about 12 rpm. If we hooked that wheel to, say, the drivewheels of a car, that car would go from zero to twelve rpm in a flash, and the waterwheel would hardly notice .

On the other hand, twelve rpm of the drivewheels is around one mph for the average car, and, in order to go faster, we'd need to gear it up. To get to 60 mph would require gearing the wheel up enough so that it would be effectively making a little over 43 foot pounds of torque at the output, which is not only a relatively small amount, it's less than what the average car would need in order to actually get to 60. Applying the conversion formula gives us the facts on this. Twelve times twenty six hundred, over five thousand two hundred fifty two gives us:

6 HP.

Oops. Now we see the rest of the story. While it's clearly true that the water wheel can exert a *bunch* of force, its *power* (ability to do work over time) is severely limited.

 

[QCRider]

Exactly. This might perhaps explain a thing or two:

http://vettenet.org/torquehp.html

It sure does.

First of all, from a driver's perspective, torque, to use the vernacular, RULES . Any given car, in any given gear, will accelerate at a rate that *exactly* matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it.

The same is ABSOLUTELY true about a snowmobile and CVT. Max acceleration occurs at the Torque peak. NOT THE HP PEAK. And by the way, I am not talking about "low end".

And lastly...

The Only Thing You Really Need to Know
Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*."

The RPM we refer to here is clutch RPM. Whatever engine makes the highest torque at 7000 - 8000 clutch RPM with relatively equal horspeower will accelerate faster. The clutch will act as a gear at lower speeds to multiply that torque and eventually fully shift out at top speed.

 

[QCRider]

By the way. I'm serious this time.

TRUCE!!

I respect your position, I just disagree with it.

Peace.

 

[stevewithOCD]

Horsepower or Torque? Let me just say this. I rode new Nytro last week & was extremely impressed. It stayed with my Apex for good stretch on lake with 20 less horsepower. The weight was probably an issue but lighter 2-smokes with same HP don't run me this close so obviously torque is the reason...BUT... i still LOVE my 4-banger sound! Not sure i can get used to that ATV type sound after riding Apex & Indy race car type sound...

 

[Laban]

I think we need to make things simpler, two yes/no questions:

Do you think that the formula to calculate hp/torque is correct ?

If the answer is yes then do you agree that 120hp@12000 rpm with a gear reduction to 8500 rpm = same torque as a 120HP@8500rpm engine ?

We're talking about torque at the clutch here.

 

[QCRider]

I think we need to make things simpler, two yes/no questions:

Do you think that the formula to calculate hp/torque is correct ?

Yes, of course.

If the answer is yes then do you agree that 120hp@12000 rpm with a gear reduction to 8500 rpm = same torque as a 120HP@8500rpm engine?

Mostly, with some exception for friction losses in the reduction gears at that one RPM they will match... What about at 6500 Clutch RPM? or 5000 Clutch RPM? or 3500 Clutch RPM when it engages, and begins to move the sled? Which sled would launch faster? One with 65 lb-ft of torque at engagement, or one with 50 lb-ft of torque at engagement? We can use horsepower here if you like since it is determined by torque. The motor that makes more HORSEPOWER at engagement will launch faster.

A larger displacement engine such as the Nytro that is less peaky with it's torque/horsepower is still a better match to a CVT than one that rises quicly and drops off quickly the way a smaller displacement high revving engine does.

Would you really want to drive a sled that the clutch engaged at 7000 clutch RPM because that is where Torque is highest? No. So Torque at 3500 RPM and all the way up to 8500 RPM means a lot as far as acceleration is concerned. This is why a broad torque curve is a good thing. Clutches do not shift instantly, I know that you would want it to quickly shift out to get max power to the clutch, and that's ok if all you are doing is racing. Imagine driving that through the woods at 20 MPH. A broad torque curve makes a much better all around sled that is just as capable on the top end as the high revving motor. It's a much less complex engine with less chance of failure, costs less to build and therefore would cost less to buy.

 

[Laban]

What about at 6500 Clutch RPM? or 5000 Clutch RPM? or 3500 Clutch RPM when it engages, and begins to move the sled? Which sled would launch faster? One with 65 lb-ft of torque at engagement, or one with 50 lb-ft of torque at engagement? We can use horsepower here if you like since it is determined by torque. The motor that makes more HORSEPOWER at engagement will launch faster.

Ok, now we're getting somewhere even though the discussion isn't about hp vs torque anymore.

Anyway, does a high-revving & low-torque engine necessarily have a narrow powerband ?

Why is is that a high-revving/low-torque engine like the Phazer does rather well from the start but has a weak top-end ?

Then there's some additional questions that one might want to think about when it comes to power just at the time when the clutch engages. First of all, can you really use it all that well on a snowmobile ?
Do you really care that much about the acceleration the first 0-5m (from standstill) unless you're racing ?