Square or round exhaust port?

DRK

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Apr 1, 2017
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Which cylinder is best for performance on a stock 66cc CG motor and why? Trying to learn.
 
Last edited:

Dan

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May 25, 2008
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If I am understanding your question correctly, DRK. I don't personally think one has an advantage over the other, other than the more fin, surface area, the better cooling capabilities.

Other than that, I don't think aside from aesthetics, one is any better or worse.

I'm looking forward to seeing what other folks think, though.
Just my 27 cents. (inflation)
 

MotorBicycleRacing

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Jul 28, 2010
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If I am understanding your question correctly, DRK. I don't personally think one has an advantage over the other, other than the more fin, surface area, the better cooling capabilities.

Other than that, I don't think aside from aesthetics, one is any better or worse.

I'm looking forward to seeing what other folks think, though.
Just my 27 cents. (inflation)
Square or round exhaust port?

OP didn't ask about the cylinder shape.

The shape of the exhaust port which you obviously can't see when the
exhaust is bolted on the cylinder.

Round should theoretically be better but on these motors there are too
many variables to consider.

That's my 2 centavo's
 

mobike91

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Sep 14, 2010
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lebanon, oregon
I'm thinking that the round shape would allow for more sound wave from a pipe to more effectively push the scavenge of the fuel mix back into the cylinder. Can't prove it, but in my mind it seems logical. Guess I'll have to build both and test ride the snot out of both lol
 

Dan

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May 25, 2008
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I did mis read.

My muffler and pulse jet guy, "Pops" (Yup, have a pulse jet for MBs, guy) Says that if you think of an engine as a pump. The hot gasses spiraling, can evacuate faster and make turns more easily. Allowing the whole occurrences of events to happen faster.
 

sbest

Member
Nov 3, 2015
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Nova Scotia
Spiraling gasses take a longer path than gasses going straight through the port. Squaring up the port at the window will help to straighten them as well as give a sharp pulse as the exhaust port opens. Once gasses are straightened the ports should be round. The header connection should be round of course.