Chuck wrote:

Rotary List:

Tracy's success with his new exhaust system motivated me to try this
experiment. I removed my original exhaust system to see if I could get some
more power and top speed. The original system I think is a little
restrictive but fairly quiet, using a tangential muffler much like Tracy's
but with a single collector inlet. I made up a new temporary system using
1/4" manifold flange, 2- 2 inch ell bends made from JCWhitney exhaust tubing
feeding SS flex pipe going into a collector with 2 1/2" straight pipe 39"
long. Length from flange to collector about 30". I did a ground run-up and
got 5200 static RPM, about 300 RPM more than original system but Very loud,
119 dB on Radio Shack sound meter inside cockpit. I then removed the
straight pipe, capped the end, and drilled about 140 5/16" holes in the aft
18" of the pipe, re-installed, and ran it again. I thought it would be a lot
more restrictive, but I got the same Static RPM and noise level. I flew it
yesterday, and takeoff roll was somewhat shorter, but at WOT throttle showed
only about 100 more RPM (5700)and showed the same 2-way GPS ground speed.
People on the ground said it was MUCH louder. They could hear me miles away!
It was uncomfortably loud in the cockpit, even with noise canceling
headphones. I may make another flight with this system, but I will be going
back to the original system. It is still holding up well. I hope to make it
to Sun-N-Fun (with the muffler - no way I would fly it cross country with
119dB to live with!) I guess I will have my Performance Prop (now its a
70x70) de-pitched a little to get the RPM up 6000 but I wanted to make sure
I wasn't losing some power in the exhaust system first. Anything else I
should try before I remove this tuned system?

Chuck Dunlap

 
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