I designed an air filter box for a Brackett foam air filter, with an alternate air source. My fuel servo intake is 4 inches in diameter. I needed to design the box based on a 4-inch SCAT hose and the corresponding alternate air valve. I would have preferred to install a washable K&N Filter but even the smaller one necessary for my engine was hard to fit in the space I had available, if I wanted an alternate air source on the same unit. I shaped the box out of foam and tested it on the firewall for fit. I covered it with duct tape and used petroleum jelly as a release agent (non-structural part). I laid three BID over it and covered it with peel ply.

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