Time to dive into the firewall forward stuff! I figured the first few things I could start with are the ones that have definitive locations in the plans (as long as you look at the right plans anyway - they are a total hodgepodge of diagrams for different engines and different variations depending on options, none of which match my setup exactly). First up, the cabin heat box. The Van's version of this box is aluminum, which doesn't make a lot of sense to me. Of all the firewall items I don't want to melt away in an engine fire, the little box covering the single largest hole in the firewall is number 1! I deleted the Van's box from my FWF kit order and ordered a stainless steel version from Aircraft Spruce. It's virtually identical, just made from SS.
I needed to somehow drill a 2" hole in the firewall. That is easier said than done. Unibits actually work very well on stainless, but I don't have one nearly that big. Knockout punches would work as well, but I don't have any of those either. That left me with trying a hole saw backed up by a piece of wood. All that did was make a shiny ring on the firewall. Stainless is tough stuff! What I ended up doing was using one of the tiny cutting discs on my Dremel. The hole is large enough that I was able to take small plunge cuts and still have it end up fairly circular after cleaning it up with a grinding stone in the die grinder.
The box came with a small tube of fire sealant. I ran a bead around the 2" hole and around the bolt holes, then bolted the box in place. The box has a flapper with an arm on it that will be controlled by a push/pull cable in the cockpit. When the flapper is closed to the cockpit, the incoming air (comes in via scat tubing pulling air from one of the baffles) just flows right through the box and out the side. When the flapper opens up to the cockpit, it swings over and blocks the side exit and diverts the air inside. It's not exactly air tight or anything, but nice and simple.
A lot of the items that will go on the firewall will actually go on top of the fiberfrax and stainless foil cover. Since this heater box actually has moving parts, I decided it should be bolted directly to the firewall. I'll just cut the insulation to go around it. I wasn't sure about mounting anything on top of the fiberfrax, but after a lot of research I discovered it's very common. The fiberfrax does compress pretty easily, so for light items (a lot of the electrical type items), the bolts will compress it enough that it'll still be very solid underneath the bolt head. For heavier items like the battery box, I'll just cut around it. I was initially being very anal about all of this, but the reality is that 99.9% of firewalls are completely bare. That's fine in almost 100% of cases. The insulation is simply to give extra time in the extremely rare case of an engine fire. Fire will not breach the stainless firewall, but the heat will. The insulation makes the cockpit tolerable even with a roaring engine fire (shouldn't roar for long if you recognize it and cut fuel). That means the ability to pilot a plane down vs not.
Anyway, all of that to say that I was initially wringing my hands over mounting things on top of the fiberfrax or cutting the fiberfrax around certain things and not having insulation there. But the point is to make the firewall better, not perfect. If I have good insulation on 90% of the firewall, even though it's not perfect, it's still FAR better than no insulation anywhere. Why that is hard to accept, I don't know. When I see the 100% solution, for some reason that makes a "90% good" solution seem like it's just a terrible thing and full of risk. Sometimes I forget that better is still excellent relative to not doing anything at all.
