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Date: Mon, 08 Aug 2005 16:54:42 -0400
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From: "Skip Slater" <skipslater@earthlink.net>
References: <list-641376@logan.com>
Subject: Re: [LML] Ram Air Flowback
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Clark,
   I have the same Performance ram air valve on my angle valve IO-540 
powered ES.  I have my filtered air coming through a K&N filter mounted 
inside my cowl which just draws the cooling air after it flows down past the 
cylinders.
   At a Lancair fly-in up in Redmond a couple of years ago I spoke with an 
owner who bought Carsten Sundin's Legacy from him.  He had the same setup, 
but pointed out that he was pretty sure that due to the open end of the 
filtered side of the valve, the low pressure area his filter was mounted in 
was actually drawing some of the ram air out before it got to the engine. 
This was my situation as well.  He fabricated another piece to close off the 
open side of the valve to isolate it when he was operating on ram air and 
saw some gain in MAP as a result.
   To address this issue on my plane, I ordered parts from Performance to 
add a second flapper valve in my system which is directly linked to the 
existing  ram air valve.  When one opens, the other closes and vice versa. 
Down low I usually see a 1.3" to 1.5" increase in my MAP when I go to ram 
air, with gradually decreasing gains as I climb higher.  While I didn't 
quantify it, the MAP rise was slightly less (somewhere on the order of 
.2-.3") before I added the second valve.
   While I can't explain the small amount of ram rise in the RV setup you 
referenced, I have to believe that the reason for the negligible difference 
between isolating the filtered side and having it open is that the filter in 
that set up was benefitting from high pressure air coming in the intake. 
Its not likely that much air could go back up that way.  In contrast, my 
filter is located in a low pressure area, which, I believe, allowed some of 
the ram air to back flow and escape through the open side of the assembly.
   I'm very pleased with the performance of my ram air setup.  At least from 
what I've seen, I think the need for isolating the open side of the 
Performance ram air valve varies depending upon the source of the filtered 
air.  In any event, the difference is small and the need for the second 
flapper is really up to the plane's owner.
   Skip Slater
   N540ES