During the original install of this engine, many cowling modifications had to be made. One of those modifications was molding a new air intake for the engine. In the interest of time, that area left a lot of room for improvement. I took it upon myself to create a much more efficient intake and airbox. The previous setup did not allow for any sort of airbox, only a scat tube from the cowl inlet to the fuel servo. For starters, my idea for an airbox involves a diffuser. Same theory as a jet engine I guess.. Inlet size x is increased to size y. This diffuser converts velocity to pressure, or in the engines case, Boost! The idea I had came out looking like a bell shape for the air to convert to pressure, then a funnel to force the high pressure into the fuel servo. Sounded good one night over a few drinks, and the diagrams on the bar napkins were very convincing the next morning..
I began by measuring the amount of space available in the cowl, the bigger the y variable the better. That ended up being 6 inch diameter, or 2 times x. 1 to 2 ratio sounds good.. I then mapped a template on cardboard paper to check clearance from the cowl and starter. This same template gave me a guide to use on the outside of the mold, a simple attempt to keep the end product round and uniform. A local stop at an aviation parts store, (Home Depot) netted some polypropylene foam. This foam has 1 key benefit I’ll explain in a second. 3 pieces of 2″ thick foam gave me my 6″ diameter needed for the airbox’ widest point. Next, I drew an outline of my template on all 4 sides of the foam block giving me a basic idea to trim the foam with a hack saw.
Once I had the basic shape, I sanded it round by hand. Not exactly scientific, but I didn’t have a better way to do it in the interest of time. 3 layers of glass and a few hours later I had a part, that was full of polypropylene foam. Here is the cool part, acetone eats polypropylene foam instantly! So a few drops down the end of the airbox, and out came a runny mess of melted foam on the other end. Worked great! As for power gains? It has not been determined yet.. down low I’m not seeing much of a gain on the old system, but up high I think it is doing its job!