After spending most of a week at the not-so-fun windshield trimming I was looking for some low hanging fruit that could give me the psychological boost of a job well done. There's several details to choose from that I want to knock out before hanging the engine. Today I decided to fabricate a cooling air exit bump. There's lots of data on VAF about how getting rid of turbulent flow and increasing air exit velocity has a couple of benefits; reduced drag as air exits the cowl better cooling efficiency. Vans also touches on this a bit in section 12 of the build manual. To that end, I decided to take a swing at fabricating one out of some scrap. The idea is to smooth out the air flow by getting rid of the drag associated with engine mount cross tubes and other stuff sticking out, as well as increasing the pressure of the air as it exits so that it's as close to upper cowling pressure as you can get it. That way you're not just dumping low pressure air into the free stream air under the airplane and causing turbulent swirlies and evil drag. The limiting factor is if you reduce the opening too much, you can get engine cooling problems. Some of the Cessna singles have a similar arrangement and I saw something like this on Robert August's Glastar as well. I'm a big believer in CAD (cardboard aided design) and thats how I started. Once I had played around with some rough shaped in cardboard and had an idea of what shape I wanted, I cut a rough blank out of some .025 scrap and took it to the hangar at the flying club then sheared it and rolled the curve there. In addition to CAD, there's also TLAR engineering, or "That Looks About Right." So there's was a little manipulation after I got back home as well. The cowl outlet is 13" wide, so this ended up being about 12" at the firewall flange, secured with four #8 screws into nut plates that I had previously installed. On the upper end, it's secured with adel clamps to the engine mount center tubes. I left about 1/4" gap around the engine mount because it would be a real drag to have a clamp slip and the edge of this thing start to saw into the engine mount. Speaking of clamps slipping, the -12 adel clamps weren't as tight on the tubes as I would like and I don't have any -11 clamps, so I added 1 wrap of silicone tape to the tube under them to give them something to squeeze down on. They aren't going anywhere at this point and the geometry is such that the body of the clamp is between the baffle/ramp/bump and the engine mount. Past the clamps, It then extends aft and up at about a 30* angle to within about 1/4" of the firewall. This may not be the final version, but whatever version I end up with, I can run a bead of RTV along that gap to seal it 100% from air leaking between the baffle and the firewall. This design allows for a tunnel of sorts which will provide some heat shielding from the exhaust for the starboard side brake line run as well as anything else I may end up needing to stuff through there. If this ends up not being the final version, I might also think about making a new one out of stainless for an additional level of fire protection since this will be the normal path of flame progression in the event of a fire in flight. The way it attaches to the firewall lip would easily allow for it to overlap a stainless belly shield as well if I decide to eventually go that way. Looking at this, I think that it might need to be a little wider to not spill air over the ends, but I'm not 100% sure. My plan is to fly without it until the engine breaks in and then experiment with this one, and maybe another version or two until I max out my performance gain. A fun project, and very rewarding to get something knocked out with a tangible result in a single day.