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Discussion Starter #1
Can anyone tell me what the torque output of the TW engine is? Either that, or torque at the rear tire. (If torque at the rear tire, what sprocket setup?)
 

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Torque: 15 Nm @ 7000rpm

But I don't know with which chainkit (14/45 or 14/50).

I think, it should be with 14/45 kit.
 

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Torque: 15 Nm @ 7000rpm

But I don't know with which chainkit (14/45 or 14/50).

I think, it should be with 14/45 kit.


Many variables affect torque. Carb jetting and fuel quality are critical.



Chain kit won't matter much as long as the engine rpm is the same. 15Nm is about right.



With real gas and proper jetting, Tdub puts down 11.2-11.3 lb/ft corrected to ST&P, which is just slightly more than 15Nm. Doesn't matter what sprockets are used, 14/55 to 15/47. Air temp and humidity makes more difference than sprockets. Chain lube makes more difference than tooth count. Switch to E10, and torque will drop to 8.0 to 9.4 lb/ft, depending on source. One fuel sold as E10 was actually E20 and only made 7.1 lb/ft. I make my living doing such dyno testing.
 

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Discussion Starter #8
So, we're talking about 11 ish ft-lb at the tire? Transmission gearing and sprocket ratio will both effect rear wheel torque vs. "raw" engine torque. That's why I asked if the torque is at rear tire or engine.

While I agree that many factors effect torque, there must be a "nominal" value published, I just don't know what it is, nor where the published torque is measured. I would assume that any value published by the manufacturer is best case, i.e. first gear and at somewhere around 7000 RPM, but I don't know this for certain.
 

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Correct. The figures I posted are 15/54 sprockets with a 428 SROZ o-ring chain with the set broken in. Close enough to stock ratio to consider essentially the same.



For those in need of explanation:



Sprocket ratio will not affect the amount of torque an engine generates, but will have much affect on how much torque is applied to the ground. This is called torque multiplication. Small changes in sprocket ratio really don't make much difference on a dyno. Switching from 15/47 to 14/55 makes about a 20% difference in peak torque reading at the rollers, all else being equal, but the difference is due to torque multiplication, not increased power output. Chain lube and wear and tire pressure can make that much difference in the real world. Chassis dyno testing is usually done in the lowest gear that does not allow the tires to slip on the rollers to minimize roller speeds. High roller speeds can lead to catastrophic equipment failure. Operators have a barrel of tricks to get the tires to hook up, but some vehicles with high output engines have to be dynoed in higher gears. Some vehicles simply cannot be tested on some dynos.



Loss from an o-ring chain compared to an open chain is barely noticable when both chains are new and properly lubed and adjusted, but it doesn't take long for the open chain to spit its lube and wear, creating more driveline loss, while an o-ring chain gradually runs smoother and smoother as it seats to the sprockets, reducing driveline loss. Within a couple thousand miles, even with a good quality open chain well maintained, losses are even. As the miles add up, the o-ring chain is more efficient, not because the o-ring chain gets that much better, but because the open chain gets that much worse. Now, if you need every spec of performance for a competition application, lightweight, high strength competition chains and frequent, consistent maintenance are the way to go. For the rest of us, o-ring chains offer significant advantges.
 

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Discussion Starter #10
Qwerty, thanks for the clarification.



Also, thanks for the O-Ring chain commentary. I haven't owned a chain-driven bike in 25 years and at that time, I was pretty much a dumb kid. All I cared about was, did it go, and if it broke how cheap could I fix it. (Dumb kid without any money.) Now I know not only that and O-Ring chain is advantageous, which I learned some time ago, but also WHY it is so.



Finally, thank you for your unsolicited comments about torque. Someone will read this and a light bulb will come on. Well said and Bravo.
 
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