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Torque Converters ....

Ok, so you have used the top-speed calculator and found a set of sprockets that offer a nice compromise between acceleration and top speed. Now what? Maybe you would like to go a little faster, but donít want to sacrifice your low-end acceleration. The next step is to add a transmission in the form a torque converter.

I receive a lot of mail asking to explain what a torque converter does and why it can justify the $200 price tag. The torque converter is essentially a transmission that changes gear ratios to match the RPM of the engine. To get an idea of why this is beneficial, imagine a car that contains a 4 speed transmission, but can only operate in one gear. Which gear would you choose? If you choose first gear, the car might take off the line with the tires squealing, but you wonít get past 10 mph. If you chose fourth gear, the car would barley be able to accelerate (if at all), but would be capable of very high speeds. 

You would likely choose one of the middle gears, which would allow some amount of acceleration but still allow for some amount of top speed. This scenario is exactly what you are faced with when using a simple clutch/sprocket drive-train as explained earlier.

Now, if the car is allowed to use all four gears, you can start out in a low gear with great acceleration, then shift into progressively higher gears and achieve a much higher speed. This is similar to what is taking place in a torque converter.

A simple torque converter, such as the Comet Tav2 Torq-a-verter, easily mounts to most Briggs or Tecumseh engines. The units incorporates a drive pulley, a driven pulley, a drive belt, and a small sprocket attached to the same shaft as the driven pulley. Once mounted, you shorten your chain and re-connect it to your rear sprocket.

As mentioned, the torque converter works as a transmission, automatically changing gear ratios as engine RPM changes. At engine idle, the unit is in neutral, and the belt spins freely on the crankshaft.

When you squeeze the throttle and add RPMs, one pulley opens while the other closes, creating a low gear ratio that is 20% underdrive (lower than original). This gives much greater low-end torque and greater acceleration.


At higher speeds, the pulleys re-configure to raise the gear ratio. At high RPMs, the combination of pulleys are at maximum and can result in an overdrive situation, allowing for top speeds greater than the original gearing.


Click here to check out Bulletline's Torque Converter for $199

So in summary, the torque converter offers

  • Lower gears than the original configuration and therefore greater torque and acceleration
  • Higher gears than the original and potential higher top speeds.

So if these units are so great, why doesnít every bike have one? The best answer is that they may not be needed. If you gear your bike low enough so that it accelerates quickly, is fun to ride, and you are satisfied with the top speed, then it would not warrant the cost. These units run between $200-$600. On many applications, there may not be space to mount the unit or there may not be an easily mountable unit for your engine type. The bottom line is that this unit is a tool that should be considered, but may not be the answer to every application.


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