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Date: Tue, 25 Aug 2009 21:42:43 -0400
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From: paul miller <paul@tbm700.com>
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Subject: GAMI testing

Looking back at my 1997 GAMI tests on the TSIO-520 engines, I recall a  
number of factors that should be considered when finding roughness in  
the lean. During the test (you should have a pre-gami test as well), I  
measured airspeed, CHT and allowed a few minutes for CHT (and turbos)  
to stabilize at each fuel increment.  My tests showed 93% airspeed on  
79% fuel at LOP for my aircraft (twin cessna) versus the ROP test.   
During the transition to GAMI mode I ran into all the sins that are  
concealed by ROP engines.  I had to:
1) repair an open sniffle valve on the intake allowing air into the  
induction system in flight.
2) pressurize the induction to find leaks in the intake couplings and  
there were many.
3) plugs, wires, mags all had various issues, highlighted only when  
LOP measurements were made.

By looking at CHT you will find cylinders that may be losing power  
faster than the other cylinders.  This can help focus the search  
beyond just injector issues.   With a lot of detective work all these  
issues disappeared and the roughness was minimized to the point it was  
not an issue once LOP was stabilized. I recall GAMI also changed out  
one injector once we sent in the data and graphs.   I used that setup  
to fly the Atlantic without requiring aux fuel tanks.   I think I had  
somewhere around 7.5 hours endurance at FL250 in the Cessna on stock  
tanks.

My main point is to consider all those factors because most small  
leaks and problems may not show up as roughness in ROP operations  
unless the problem is severe.

good luck, I think it worth the trouble if you want better endurance  
or fuel economy.

Paul Miller
Legacy RG