The purpose of the GAMI Lean Test is to quantify the fuel/air ratio balance in the engine either before or after installing the GAMIjector® fuel injectors. Knowing this balance, and the value we call the GAMI Spread is important because it will tell you how much you can benefit from GAMIjectors® if your engine is not already equipped with them, and it will tell us if we need to adjust your engine balance if you are already equipped with GAMIjectors®.
The GAMI Spread is calculated by determining at what total engine fuel flow each cylinder reaches peak exhaust gas temperature (EGT) and subtracting the lowest flow from the highest flow. Most engines are considered to have good fuel/air ratio balance if the GAMI Spread is less than 0.5 gph.
The following method assumes that you have some instrumentation to measure the EGT on each cylinder and the total engine fuel flow (this may be digital or analog). While following this test method, we highly recommend that a safety pilot accompany you. We also recommend you keep the cowl flaps open, if so equipped, and you perform the test at 65% power. It may be necessary to use a lower power setting, as required, to keep the CHT under 400°F and/or the Turbine Inlet Temp (TIT) under your max continuous redline.
With this method, you record EGTs (and CHTs optionally) at small increments of fuel flow adjustment from around 2 gph rich of peak EGT to some point lean of peak EGT. You want these lines of data to be in the smallest practical fuel flow increments... 0.2 to 0.3 gph works well. You will also want to use the smallest EGT resolution possible. For many monitors this means 1°F, though 5 or 10°F is the smallest for some monitors. 1°C resolution works fine, also. It may be necessary to use the monitor's "lean find" or "lean assist" function to find the 2 gph rich of peak starting point. The reason for starting 2 gph rich of peak is to prevent you from either taking much more data than necessary, or starting the data collection too late to capture enough information.
You can download blank copies of this test form here, or create your own.
