I had swapped out my Sonex supplied air filter with a K&N filter (4”x2”) as recommended by Jeff Shultz during my build. During my test flights I’ve struggled to get above 3000 rpm’s with my Jabiru 3300 Gen4 and AeroInjector. Last week on the same day I flew a couple of short test flights back to back, with and without an air filter to see if I was choking my air inlet. Without the air filter I hit 3150 rpm’s, so there was something there!
I have the tricycle gear so not a lot of real estate behind the engine like a couple of Sonex tail draggers here so I couldn’t go with their larger air inlets without some complicated ducting.
After a long internet search I found a 4”x3-5/32” Baldwin filter from Zoros, easily DOUBLE the area of the K&N. Anything bigger than 4”x4” will not fit. Link below. Will install and try it next week, of course after I get the $9 in longer bolts that required $15 in S&H. Next step will be to rich the AeroInjector a bit more.
There’s an old thread that explains how I hung the filter. Some of the pics populate directly, and some of them you need to click on the icon and go to the wayback machine.
I think part of the confusion is that the “proper” K&N filter that many of us have used with the AeroInjector is discontinued. It was the “E-4310” model and was about an inch taller than the model in your photo (so it provided a lot more airflow). I don’t think anyone makes a replacement in the same size (at least, not as a reusable/lifetime filter).
In the Sonex, the air in the cowl under the engine is warm - like really warm in the summer. It’s effectively carb heat. That’s why a bunch of us provide fresh air to the air filter on the aeroinjector. It turns off the effective carb heat of the Sonex design. I think I picked up about 150 static RPM when I went to fresh air induction.
Super interesting. Right now my focus is flight testing…. Got about 8.5 hrs left to go, then fly fly fly. This’ll be something to look into more this winter shutdown. Need to pull my Jabiru and get it to Arion for the crankshaft replacement advisory, my SN is on that list. Will be a three week downtime and will have a punch list by then to work on.
Here are a couple of interchanges for the Baldwin PA4557:
Donaldson DCI P530643 - NAPA catalogs it, currently out of stock.
Napa Gold FIL 2362 - about $25, ships to your local store for free.
Grainger has the Baldwin, if you have one near you.
