This chapter is about firewall accessories after it’s been built. For now because I’ve gone for Mike Melvill designed cowls, my firewall is more than 4 inches too short! He designed his after a NACA scoop was installed. While he later filled in the NACA the firewall had a longer area where the opening used to be. This legacy has me with his design cowls but the plans firewall, hence an ‘extension’ is required.

I hot glued a board flush with the back of the firewall as a base to build off. Then I got the bottom cowl and drew a rough line to get an idea of how much more meat I needed.

I used a paper template to get the lines I needed. Its much easier to trim paper than wood. Then I added a bit for good measure as you can see in the picture. It will be easy to trim afterwards and get a perfect fit.

I cut this out of the same plywood I’d used on the rest of the firewall. The curve was a bit of a fiddle. I used West epoxy as flox and, after some release tape on the support board, I glued the extension in place and clamped it overnight.

Then I thought… well given its clamped, I can route out some slots and fit and glue my reinforcement inserts now. My route depth was just short of all the way through so there was a little support left at the back.

Today I routed and sanded the insets smooth and prepared both sides for glassing.

Here’s the inside, prepped and ready.

I used one ply of BID at 45 degrees bias as usual both front and back. Even before this extra glass, the join feels very strong.

Post trim and peel ply removal. Lets call the firewall, the correct length and good.