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All is quiet today, so I'll write a post on exhaust backpressure and
ask a question...
The dual crossover exhaust sold by Lancair for 4 cylinder Lycomings
is designed to achieve minimal backpressure by allowing the sequenced
exhaust pulses from opposite cylinders to flow down the pipe without
"running into each other".
Somewhere, I've read some in-depth theoritical ideas on exhaust
which stated that backpressure is minimized if the exhaust tube terminates
in an oval (rather than round) shape. I decided to go for any incremental
improvement (they all add up and I'm trying to exceed the speed of sound!).
It was easy to squeeze my exhaust pipe extensions into an oval shape
by placing them between two short 1 x 4's and gently squeezing them in a
vice. Besides, it looks nice!
Is anyone else knowledgeable of this? Is what I read correct?

Bill Rumburg
N403WR  (Sonic bOOm)

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Please send your photos and drawings to marvkaye@olsusa.com.
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