I see a lot of times where people run as much as 2 ½ - 3 to 1 on the primary. Now that means, yes, the clutch is spinning 2 ½ - 3 times slower than the engine clutch, but it’s absorbing 2 ½ - 3 times more torque. This means you’re trading less heat at the expense of more effort.
Having two chains and four sprockets has to be absorbing some horsepower. That primary chain is spinning really fast.
If you’re racing a two cycle, and you can’t get a conventional two sprocket setup to a low enough ratio, then the power losses of the jackshaft might be justified. It’s a tradeoff.
Seems to me if you don’t need the lower ratio you can achieve with a jackshaft, there’s no need for it.
Comments, compliments, criticisms and questions always welcome.
If the data does not support the theory, get a new theory.