Update #2 - Aluminum shielding
I was able to make some pretty cool progress after looking at the retail heat shield products. I was able to get a look at some of it at Vic Hubbards and it's essentially fiberglass weave with a thin foil layer woven over it. It's nice stuff, but requires gluing it down or using a bunch of fasteners. I wasn't sure I wanted to try gluing it down or trying to get a bunch of screws installed in such a tight space. So I decided to try another route first.
I'm not sure why, but buying aluminum sheet in stock pieces from the hardware store is rediculously expensive. A 4" x 18" piece of .025" aluminum was over $30 at several different stores I checked. So I improvised and found a much better option at a super cheap price:
Aluminum venting is the same thickness and about the right size when unrolled. Price was $4.95.
I saw some 30" diameter water heater drip trays that would have worked as well and were reasonably priced.
After doing some test measurements, I discovered that the radiator fans were not blowing much heat from the radiator itself, but when that air passed the exhaust manifolds, it really heated up. So I fabricated the aluminum sheet into a shape that fit against the firewall and right behind the manifold. The idea being to try and direct the heat down and under the truck where it can dissipate in the air rather than soaking into the firewall.
Here's the shield mockup in place over the hottest part of the truck. I just taped it in place for the test so it wouldn't fall off, and then did my test drive routine to warm it up.
And here's the numbers from both this test and the previous test:
Test#1 (aluminum foil under floor, firewall exposed)
Ambient = 75 degrees
Firewall = 113
Front half of floor = 94
rear half of floor = 91
Test #2 (Aluminum firewall shield, floor exposed)
Ambient = 77 degrees
Firewall = 93
Front half of floor = 110
Rear half of floor = 93
If you look at the firewall numbers, you can see the temp went from 113 (no shield) down to 93 (with shield). That's a 20% drop when the ambient differences are factored in and is only 16 degrees above ambient. That's a very noticable difference. Pretty good!
The other numbers to notice are the "Front half of the floor" (the area under the gas pedal). After the shield was installed, this area is now the hottest area and is even hotter than Test #1. I assume that all the heat being blocked at the firewall is now being directed under the floor. So the heat is moving in the right direction.
So it looks like the idea can work quite well. I'll probably add another shield under the floor to block more of it. I also may be able to copy the professional shield products and sandwich a layer of fiberglass matte between two layers of aluminum and form the edges so they're not sharp and maybe even make it somewhat waterproof.
Thanks for all the pointers in the right direction everyone!
