Bill--

Thanks for the speedy reply. I built my own airbox (see photo) because I wasn't comfortable with the unbalanced factory design although it was more compact than the one I built. In the recently posted Lancair Accident List, the 1991 fatality in Titusville, FL was caused by the aluminum flapper in the factory breaking off and lodging in the carburetor (I knew the builder.) I should say that this wasn't the fault of the factory design; The builder used too-thin aluminum for the flapper and kept flying when the engine started running roughly. Anyway, I preferred a balanced airbox design with the ram air coming in the front, and the heated air coming in the back side of the airbox. The aluminum diverter just rocks either forward or backwards and diverts the desired air up into the carb. The "unwanted" air exits the bottom.

The "air scoop" at the front of my cowling is circular and roughly 2-1/2" I.D. I moved it forward to just behind the prop. The intake expands to 4" diameter over about 12". The idea there was to slow down the ram air velocity by half to more closely match the velocity being sucked into the carburetor. The expansion tunnel on the lower cowling is connected to the airbox with a short section of 4" SCAT tube.

I have been considering the K&N cone-shaped filters to fit inside this 4" duct, but was concerned that they weren't designed to handle the high-velocity air from the ram air intake. I guess that's not a problem because the ram air has to slow down to match what the engine wants. Also, the smallest cone-shaped filter K&N makes has an opening of almost 6", and my airbox intake is 4" so I would have to cut down the K&N filter somehow to fit.

This is one area where I don't want to experiment very much.

--John




This is looking down the front of the airbox with the diverter in the ram-air position:



This is with the diverter in the carb-heat position. You can see the 2" air dump hole at the bottom. Note that the diverter is captive, and can't fall off under any circumstances.




On 1/14/2014 10:47 AM, Lancair Mailing List wrote: