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Flow Matching Fuel Injectors

These days many pilots operate their engine "Lean of Peak" (LOP). There is plenty information about this on the internet, but essentially the benefits are much lower fuel consumption and a cleaner burning engine for a trade-off of a small reduction in airspeed.

On many older style engines, it helps to run LOP if the injectors are flow matched.

This is a lot simpler than it sounds, and yields results that make it well worth while. It does require having EGT gauges and an engine monitor.

On my Lycoming engine, I performed what's known as a GAMI SPREAD test. Essentially you fly to about 8000ft and very slowly lean the engine until it just starts to falter (or close), repeat it a few times, then download the data. Savvy Aviation offer a free account that analyzes the data, with a GAMI SPREAD function.

It showed that when I moved the mixture to lean of peak (LOP), 5 of the cylinders were operating cooler and lean, but the #1 cylinder was still quite rich and operating near peak EGT. This meant that I wasn't able to run fully lean of peak at low altitudes where the ambient temperature was warmer, or the #1 cylinder would be too hot.

I purchased some smaller restrictors from Airflow Performance, and installed one in the #1 fuel injector. This takes about 3 minutes. The injector remains in place while you undo the top nut, change the restrictor, replace the nut, and go flying.

This now showed the #1 cylinder to now be running leaner and closer to the other cylinders, meaning that they all peak together, and therefore they all sit LOP together. It's now easy for me to run LOP at low (or high) altitudes, for a large fuel saving.


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