Horsepower increase

[nanard289]

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Hi Dave,

Your local machine shop dealer has a good approach: you have to replace the muffler by a pipe to keep a minimum exhaust pipe length. By this way, you will improve significantly your engine performance for following reasons:
First, when you remove the muffler, the exhaust gas way is free (without zigzag) and the pistons take only few power at the crankshaft to push the exhaust gas in the headers.
Second, inside the headers (at the middle), exhaust gas are pushing in front (to output side) but they are pulling in back (cylinder side) until to create a vacuum. This phenomenon is amplified with the gas velocity. Consequently, (if the exhaust pipe is long enough to favor it) due to the vacuum in the cylinder, the fresh gas will be strongly sucked when the inlet valve will open even if the piston still rising (that is the reason why you have to tune your carb). If the exhaust pipe is too long the gas will lose velocity and will block the inlet gas (that is the reason why you have to evaluate the total header length).
To conclude, if you replace only your muffler by a pipe (with a good carb tuning), you will win some HP. But if you change also your camshaft to optimize the vacuum phenomenon (to anticipate and to increase the inlet valve opening) the power gain will be more significant (but it is not a 10 min. operation!) Anyway as say Cranky, the open pipes will increase your fun factor and that is a very strong argument.
Bernard