I am early in Phase 1 testing on the RV9A with 17 hours on it so far. It has performed extremely well and has only had a few minor glitches to deal with. The engine is running strong and oil consumption stabilized in the first 4 hours. Early on I noticed I had the typical fuel distribution issues common to carbureted Lycoming engines. Wide open throttle produced very uneven EGT’s as well as causing cylinder head temps to be 50 to 60 degrees apart. (Forget lean of peak ops all together) Simply closing the throttle slightly brought everything inline. Not the best situation, so I started doing lots of research on correcting the issue. I found several articles from sources like NASA, Navion, etc. pertaining to uneven fuel distribution caused by turbulence entering the carburetor from poor air box design. Since I fabricated my own air box I became convinced this was the source of my distribution issues. I found over the years several manufacturers had to include air straightening devices in their air box to correct similar issues. Most consisted of a few well-placed blades to help straighten the air and direct it through the carb. I didn’t want to go that route, so enter 21st century materials. Cars today use a honeycomb airflow straightener in front of the airflow sensor to straighten the air and prevent inaccurate readings caused by turbulent flow. The material they used appeared a little restrictive to me for use in a 320 cubic inch engine, so after some searching I found someone who sold a replacement with 1/8” honeycomb cells made from aircraft grade aluminum and 1/4" thick. I took the material, sandwiched it between two pieces of aluminum, potted the thing together with epoxy with spacers in the bolt locations and mounted it between the air box and carburetor.
I now have 4 hours on it since the mod and the results so far are impressive. I gained 50 RPM in static run up. The engine is smoother and more responsive. The really amazing part is, it will now run 20-30 degrees lean of peak with fuel flow under 7 GPH . I feel more could be had if I had electronic ignition to help light the lean mixture as anything over 30 degrees LOP causes an intermittent slight miss. I have more testing to do before I call it a complete success, but at this point I am convinced it’s a win.
Disclaimer: I am not an engineer and I didn't stay at a Holiday Inn last night. Do your own research and choose wisely
We are talking about a powerplant modification. It's in early testing and I make no claims as to it's safety. If you choose to
make a modification like this you do so at your own risk.