Over on the Locost forum, someone built a diffuser using 1/8″ (3mm) ABS sheet, doubling it on the strakes. I’ve got some left-over black 1/4″ (6mm) HPDE sheet which might work well for the strakes due to being potential wear items. I’ll have to make templates and see if there’s enough material on-hand. Given how diffusers work, it’s tempting to extend the end plates lower than the floor, though that makes them the lowest point on the car…
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!
The wings – not yet fabricated – will only be mounted for track events. I’m not impervious to what people think (partly because it can affect book sales) but also because I’d feel silly driving on public streets with them. While technically functional at all speeds, they’re realistically pointless at legal road speeds, so it’s sort of a lose/lose proposition. I mention this now because to a somewhat lessor extent, the same applies to the diffuser.
The diffuser will be a 24 x 48″ (610 x 1220mm) panel with the forward edge attaching to the rear-most cross tube. Due to the muffler, it’ll have a small angle toward the front, then a larger angle behind it.
This Racecar Engineering article and Willem Toet article were both very helpful (though the latter was obviously not proof-read!). Before reading the articles, I was going to leave out the strakes (the vertical vanes always seen on diffusers, but the figures graphically show why they’re a good idea. The articles were found while doing a Google search to answer whether a flat or curved diffuser works better. While neither article answers this directly, it appears that the sudden slope change at the front edge is necessary to initiate the spiral air currents drawn in from the sides. (On a related note, most forum discussions about diffusers are very inaccurate, go figure.)
Getting back to the question about street use, I’m sort of on the fence concerning the diffuser. Like the wings, even if it works, it’s of little to no practical benefit at legal speeds. Unlike the wings though, it’s not quite as “in-your-face”, being mounted down low. Also, there’s the practical issue of where to keep it when it’s not on the car. The wing assemblies will be tall and slender, and can be stored against a wall out of the way. Not so much with a large three-dimensional diffuser assembly. As of this writing I’m leaning toward leaving it on the car and putting up with the increased boy-racer look. That said, if I can drive down a leaf-covered street and kick them up high in the air behind me, that’s so totally worth it 🙂
Before anyone says “well what about the pretentious air intake on the roof?” Unlike the wings and diffuser, cooling the intake charge is of benefit whenever the engine’s in boost, which is often, so it stays.
I’ve had enough – don’t worry, it’s not about the car.
Visiting various websites, I’ve had enough of the increasing number of ads and the extremes to which some website owners will go to in order to increase ad revenue. Click-bate – and more and more regular sites – are turning into thinly-wrapped delivery systems for Google ads instead of actual content, which is being relegated to less and less screen space. What content is left has been calculated to be the bare minimum required to get people to click the next page. So to twist a saying, I’m putting my mouth where my money was and am removing Google Adworks from this site.
I know many people didn’t mind, but what they may not realize is that when webpages appear to hang while opening, it’s because Google gives priority to all the sidebar, header, footer, and embedded ads, ahead of the actual content. I don’t like them deciding that their revenue is more important than the content people came to see in the first place.
To be honest, Adworks never made much here, so I’m probably being a hypocrite; I probably wouldn’t be as righteous if it was making $10,000 a month. But it isn’t, and no longer feeling a bit like a prostitute is worth more than what their system was paying.
Cleaned the bottom and rear of the car, though it was impossible to get at all the oil. I didn’t want to use any sort of sprayer that drives water into the wiring or chassis tubes, so I’ll wait for the oil to absorb dust and fall off…
After that, it was time to install the new exhaust, this time with a Borla muffler, mostly because it’s stainless but also to test the claims of great muffling and low back-pressure. The exhaust is set up so that it disconnects downstream of the flex coupler with a V-band for track events, and a short right angle extension can be swapped in, much like how the exhaust was before today. Both wastegate outputs are also fed in upstream of the muffler – no point cruising quiet(er) but attracting the wrong type of attention while under boost.
The muffler works really well (Borla PN 40359), I’m pretty happy with it. The picture from the rear shows how it’s leaned forward, to miss the future diffuser. This leads into something I’m working on, to solve how Midlana’s been looking a bit “unkept.” One issue (in addition to the engine cover) is the chopped off lower rear panel (crunched when the car backed off-course at Willow Springs then cut off because it wasn’t repairable). The plan is to fabricate a one-piece engine tray/diffuser of aluminum or stainless. Whatever the material, the nearly 48″-wide sheet has to be thin/soft enough that it can be curved upward to form the diffuser. At the same time, I’d like it thick enough that it can serve as structure under the engine, something of a contradiction. A middle ground might be to have a shop roll the curve into it for me.
As mentioned before, the air filter’s being changed to pick up air from the side inlet instead of sucking in hot engine compartment air (now hotter because of the muffler below it). The ducting and different air filter element is on-hand; the new filter is better suited to being enclosed and fed via ducting. After finishing the muffler, the new filter was installed without the ducting just because, the large hose clamp tightened, and I headed out for another test drive.
During the drive on my newest favorite road, I saw two Alfa Romeos GTVs (my favorite model) pulled off to the side, the owners chatting. Further on were another 3 or 4 more, one with its hood up. I stopped and asked if they needed any tools. They laughed and said “we drive Alfas, of course we have tools!” We chatted some about Midlana and then I was on my way – thankfully not trailing a stream of oil like last week!
With the muffler working so well, new sounds are detectable now, and unfortunately, one sounds like engine knock under full boost. What’s unclear is whether it’s always been there and I couldn’t hear it, or if the (assumed) added back pressure from the muffler caused it. I’ll log a drive to see what’s going on; maybe it’s just something that sounds like knock. If it’s the real deal though, boost will be dialed back a bit :).
Stopped for gas on the way home and half way through filling the tank, I saw something move out of the corner of my eye – the air filter had just fallen off the turbocharger, hah. How it managed to stay on the vibrating engine through the entire drive and only fall off right then, I don’t know, but I was happy to see it happen. The hose clamp worm screw housing had contacted the compressor housing, giving a false indication of being tight – fixed.
No oil leaks on the test drive, though there’s still oil from the original leak coming out of the woodwork. What didn’t help the oil leak situation was the engine tray being off the car. Not only did this allow the oil to be blown aft, but the open rivet holes allowed some of it into the chassis tubes, only to later drip out when it feels like it.
Lastly, alternator output remains at 14..0-14.5V during the entire drive, so no issues there.
Oh, ran across this pretty cool looking (and free!) PC application for designing mechanical linkages. I haven’t used it yet but it could be useful for future projects :).