If the exhaust pipes are run into a common collector then allowed to expand
then the gas is necked back down to the same size as a single pipe of the
incoming pipes.
The length of the pipes as they enter the chamber should vary so that the
cylinder that fires first scavenges the exhaust gas from the next firing
cylinder. the difference in the length of the pipes in the chamber should be
no greater than the diameter of the pipe.
All of the pipes should be the same length from the center of the exhaust
valve to the end of the pipe in the chamber. Orginally we thought that the
pipes should be the same length from exhaust valve to exit as is the intake
from air inlet to intake valve.
But after several sets of pipes and much testing and modifing we found that
we couldn't tell the difference. Our biggest gain was from the expansion
chamber, much different sound also.
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