20 May 2018

Worked on two projects: the cold air intake and the diffuser.

Unlike how I normally do things – scratch-building everything – this time I wanted to see if I could find something “off the shelf” to serve as the air filter enclosure. After wandering around half a dozen stores, a stainless double-wall ice bucket (complete with woven bamboo weave) looked “promising”, mostly because nothing else in the kitchen sections was even close. Removed the bamboo, then used the “death wheel” to cut out the inner wall. It was pretty amazing how perfectly it fit the conical air filter – though I did test-fit it in the store. What still has to be added is a 5″-diameter extension to pick up the duct hose. At the other end, another fabricated duct will feed air to the hose from the side air inlet next to the dry sump tank. It’s either going to be composite due to the oddball shape, or a rather curvaceous aluminum assembly.

Diffuser: after reading that excellent article, given that the bottom of the car is flat from front to back, the diffuser might actually have a chance of doing something. It’s a 24 x 48″ (609 x 1218mm) aluminum panel, with a lot of mockup work. The forward edge will be captured by the aft edge of the engine tray. Right now I’m thinking of aluminum angle below to support the strakes (yes, that’s the term), and another piece across the rear edge to prevent bending and to (very optimistically) perhaps even act as a Gurney flap. That should make it rigid, but it’s still has to be supported, either off the side panels or via tubes or cables off the inboard chassis. Mostly because of the muffler, the diffuser angle ended up being 13 degrees. Yes, I know, everyone says the maximum divergent angle should be 7 degrees, but as the article notes, diffusers run at lower speeds and with larger ground clearance can handle bigger angles. In any event, something will close off the current open area around the exhaust, probably screen just like above, though the shape needs some thought to not totally mess up the appearance.

There is a bit of concern about the nearly 2-ft extension behind the rear axle. For example, going over speed bumps, not currently a problem, could become so at certain speeds, where as the rear of the car passes over and down, the suspension compresses somewhat below ride height as the shocks compress, so the speed bump could end up kissing the bottom of the strakes. I’m trying to plan for that possibility, so that the worst that happens is a bit of aluminum gets bent, rather than it hooking on the leading edge and ripping the entire assembly off the car!