Quote:
Originally Posted by pete
It's called the "Magnus effect"... only comes into play when the sphere is spinning..
is why a tennis soccer player or baseball pitcher can turn the ball in flight...
it produces a low & high pressure area on opisite sides of the sphere .. high pressure side pushes the sphere into the low pressure side turning the sphere in flight.. also why muskets & canons had unrifled
barrels to stop the musket ball spinning 'turning in flight"
they used this force to power a ship... if intrerested google "flettener rotor"
nature knows best..... sharks have a rough skin for this very reason
it traps a thin layer of water that makes the shark very smooth & slipery..
exhuast wrap... hotter the exhuast gasses the thiner they are so they can travel
faster...
....
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Yeah, Pete, mentioning sharkskin explains the issue perfectly. That's why polishing the inlet tract in the head is a poor idea. Polishing inlet tracts was a big deal in the 1920's and 30's. They got better performance because the inlet tracts in those days were rough castings, so any smoothing of ports made a big difference. A pressure die cast alloy head is not the same thing as a sand cast iron head. Because, for cost reasons, and production numbers, they took great care in designing the die cast molds. When they ran these engines on the dynos, and then polished the ports, the polished port engines were always a little lower in output. Took a while to figure out why. This little engine has a really great die cast head. Actually all of the castings are a tribute to the foundryman's craft.