While travelling back to California from a summer of thunderstorm-dodging in the eastern half, I had the chance to visit General Aviation Modifications, Inc. (GAMI)GAMI lean test. My spread was only .6-.8gph between the first and last cylinder to peak, while their literature spoke of 1-1.5gph spreads in unmodified engines. (if you do the lean test, you will want your Arnav EMM to report in one degree increments)
I arrived on Sunday afternoon, and was met as promised by the company president Tim Roehl. I cooled off with a bottle of water as Tim and George pushed my plane into the hanger and gave it a very professional oggling.
After a night with GAMI’s crew car at the hotel they booked for me (you should be getting the feeling I was very well taken care of) I spent all of Monday at the plant. While they were installing the GAMIjectors they’d previously customized to my Lean Test’s, Tim explained their results with our tuned induction engines. They have found the air flows to be very well balanced in the O-550N’s, which means they can be more precise with the fuel flows. We reviewed the water flow tests on my OEM nozzles and compared them to the lean test. We saw a direct correlation between flow rates and the spread in the lean test, which confirmed the well balanced airflow theory. Tim now feels that getting balanced fuel flows well below .4gph yields considerable benefits in LOP operations, and that this is very achievable with the tuned induction engines.
The nozzles were in by the time we finished, and I went up for a test flight with George. We ran a lean test, and found the spread down to .4gph. It was a big improvement, but George wasn’t satisfied. He also observed that my full power fuel flow was low and was very concerned about that.
George believes that the most destructive thing we do to our engines is full power sea-level takeoffs at anything less than full 27gph fuel flow. He’d actually prefer the fuel flow to be at 28 or 29gph, and believes OEM’s skimp here at the cost of our engines. These rich of peak (ROP) full power runs develop the highest peak cylinder pressures and are most sensitive to being insufficiently rich. He considers this a Fix-on-Condition item, not one that can wait for the next oil-change.
Tim and George took me to lunch as the maintenance team got to work tweaking my #4 injector and adjusting my fuel flow. After lunch we found the injector was done, but the fuel flow was proving to be a bear. They had to remove the oil filter to get to the adjustment screw, and then found it was very close to the end of its travel. After much struggle, they had the adjustment made.
note: Cirrus recently sent out a SB from Continental about fuel flow adjustments. That procedure works by adjusting to a calibrated fuel pressure. George thinks that is an inadequate procedure since if adjustment to that pressure results in a fuel flow of less than 27gph, it is unacceptable. This seems true since only 1 week before my engine had been adjusted to that bulletin during its annual at Airways. He adjusted my fuel flow based on my factory fuel flow gauge. I asked how he know the gauge was accurate, and he said because he could tell from the CHT’s during takeoff. Before the fuel flow adjustment I had 1 CHT up to 380, afterwards they were 360 and below. I realized this is why we need the fuel pump on during takeoffs and go-arounds, as the extra fuel pressure boost is necessary to get this essential fuel flow.
On the second flight, George saw that the engine was so smooth we didn’t need to rerun the lean test, but instead spent the flight on a tutorial on LOP operations. Which will be subject of a seperate trip report!
But overall, anyone who is considering GAMIjectors should also consider the pilgrimage to Ada. Perhaps combine it with the Advanced Pilot Seminar being presented on engine mangement by John Deakin, George Braley and Walter Atkinson. George video’d our test flight and if it doesn’t come out too bouncy from the turblulence, you could well see shots of the Arnav in the seminar!
-Curt