D
Deleted member 12676
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Below is plans specifically for a 69cc Grubee engine with its exhaust port raised 1.2mm (to 28.1mm from cylinder top) for an exhaust duration of 150 degrees. (Standard is 141 degrees). The transfers should be left mostly as-is other than matching the left and right side so that they open at the same piston position.
Theory of torque pipe: The straight extension in the converging cone (the baffle) spreads out the return baffle wave for a broader range of rpm in which it has the same effect of preventing fuel loss out the exhaust port as the piston ascends (to increase delivery ratio which boosts power). And the return diffuser wave is maximized which gives the effect of the engine being more torquey. And the waves return timing is scientifically calculated for maximum power due to complete harmonization between pipe and engine. That timing is determined by the cones distances from the engine (measuring along the pipes interior).
ps- in case it isnt obvious, the header distance is 430mm. Divide millimeters by 25.4 to get inches. The ideal stinger length is 8.5" inside the pipe, and 9.5" sticking out of it. But that isnt critical.
Theory of torque pipe: The straight extension in the converging cone (the baffle) spreads out the return baffle wave for a broader range of rpm in which it has the same effect of preventing fuel loss out the exhaust port as the piston ascends (to increase delivery ratio which boosts power). And the return diffuser wave is maximized which gives the effect of the engine being more torquey. And the waves return timing is scientifically calculated for maximum power due to complete harmonization between pipe and engine. That timing is determined by the cones distances from the engine (measuring along the pipes interior).
ps- in case it isnt obvious, the header distance is 430mm. Divide millimeters by 25.4 to get inches. The ideal stinger length is 8.5" inside the pipe, and 9.5" sticking out of it. But that isnt critical.