I’ve been thinking of how I could build this intake manifold with the tools and materials I have access to here at Casa de El Poeta without having to purchase anything beyond the cloth and resin and molding materials like peel ply and mold release. I’m not coming up with much.
Part of the problem is making the molds for the runners that need to be used 8 times to build each manifold, probably more because some of the early parts probably won’t unmold without damage to either the part or the mold. One thing I have been thinking about is using 4 molds per runner and building the runner in 2 parts and then using the tape that will make the runners strong enough to support the plenums, throttle bodies, and the fuel rail and injectors, to also glue the halves together. I don’t have to be concerned about the surface finish of anything because the peel ply will give a textured finish as long as the molds aren’t too bad.
And as I was “rubber ducking” this into the blog post, I came up with a solution for building the outer mold for the runner by using the inner mold as a plug and using the sanding and polishing process on the inside surface of the outer mold to get the clearance between the inside and outside for the material to go. This will also ensure a high degree of compression in the composite. How to rubber duck a problem. If I had the vacuum pump that most composite molding systems use to remove air from the mold and part to use atmospheric pressure to force resin into the part and force excess resin out of the part I would not need the inner part of the mold, but by using an inner and outer mold I can get much higher pressure on the composite to distribute and squeeze out the resin to a much higher degree. Basically I can clamp the two parts of the mold together at much higher pressures than the roughly 15 psi I can get with a “perfect” vacuum. This is part of the “forged carbon” process that uses bits of carbon tow and chopped fiber much like the “chopper gun” method of making fiberglass parts, but with much less resin in the part.
I have been searching the web and the consensus seems to be that just about any resin that resists gas will work because of the limited exposure from the spray of fuel from the injector compared to the 24/7 soaking of fuel tanks. Basically any of the hard-curing gas tank liners will work for this application, but I will have to paint the finished part with a UV-resistant coating to sunscreen the resins and prevent UV degradation. I see this as a minimally problematic solution. Basically I will have to paint the manifold white after curing, instead of leaving the part natural. I won’t have the “cool” factor of a natural CF part finish, but the part will remain strong for a longer period of time, talking decades of use, compared to a couple of years without the sunscreen coating.
I’m still thinking about how to make the plenum, and whether to mold in the injector bungs or glue in aluminum bungs after molding the plenum. Molding has the potential to reduce the weight by a few ounces, but gluing the bungs has a higher degree of precision fit. Not to mention that molding the bungs requires a high degree of precision of the inner mold that I probably won’t get with what I have to work with. And I’m getting hungry and I need to make food to consume so I have to be away from the computer while I cook the food. It’s not so hot that I’m going to cook. It’s only 103°F and human flesh starts cooking at 145°.
Witch on a Bicycle 