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

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