next wonderment - why are exhaust manifolds typically designed to get larger dia. as more tubes attach downstream (as with the waste plumbing in buildings), when, in reality, the flow is thru only one tube at a time?    kevin (turrentine renesis coming soon!)

Kevin,

With rotaries they have found that a constantly expanding exhaust helps keep the pulse moving. It also keeps the LOUD moving. The Rotary will tolerate some back pressure, but since there is no exhaust valve it helps to be sure that there are as few reflecting surfaces as possible until the port is closing.

Bill Jepson