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M20C/D/G owners- what does your Powerflow fart can look like?


DXB

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So I just had a Powerflow exhaust installed to replace my 22 year old, 2300 hour Knisley exhaust. Pretty disappointing so far. I notice no obvious gain in cruise speed, despite the carb'd birds supposedly benefiting the most from this mod.  If anything, it seems a kt or two slower though I don't have a proper controlled comparison :huh:.  One possible reason came to mind.  The Knisley tail pipe was both much thinner and also angled pretty horizontally. In comparison, my Powerflow tail pipe is enormous, angled much more vertically, and protrudes much further - it looks like a massive source of drag.  Perhaps this unfortunate feature negates any benefit from horsepower increase?  

Interestingly, I saw another C model today with a Powerflow, and its tail pipe protruded 2” less and also was not as vertically angled (though still more vertical than my prior Knisley).  It is not at all clear to me what accounts for these differences - perhaps manufacturing variations in the exhaust? 

Anyway, how low does your Powerflow tail pipe hang? Mine is almost to the bottom of the nose gear door.

Picture1.jpg.606e6921de3000ef5faa3d33a6c9a0ae.jpg

 

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Large diameter pipe... should have less back pressure...

If the air flow has improved through the engine... are you seeing any FF increase to match?

Have the peak EGTs changed at all... this may be hard to see because of OATs changing as well...

Of course... swapping a mag may hide things a bit as well...

To benefit from the gains in airflow...

  • More air has to come in... clean or hi-flow filters can help on the front end...
  • More fuel has to be used to match the extra air coming in...
  • The exhaust has to have less back pressure...  to improve evacuating the exhaust out of the cylinder...

To only benefit from the lower exhaust pressure would be a pretty small gain...  but that gain would be free... no extra fuel being burned... :)

There are different versions of the PF exhaust... and how streamlined they are...

Mooneys don’t like to stick long pipes, straight down...

Find an O to see how streamlined they can be... not perfect... but pretty streamlined...

benefits of the pipe hanging down... less CO near the cockpit... the larger pipe will allow for cooler exhaust... from more rapid expansion of the gasses...

So many things going on at one time... collect data... even when it may not seem to have any benefit....

Cruise data @8k’ has got to be interesting... 

What timing is your electronic ignition running at in cruise?

Best regards,

-a-

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