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I'm in the process of doing a rear spoiler for DSP autocross as well as a splitter to match. I've mocked the spoiler up pretty well and will be getting the Lexan cut next week or maybe the one after, still have to make some decisions on how I want to support it all and how many holes I want to drill in the car. I'll tackle the splitter as soon as I have this whole rear thing sorted out.
The plan is to do a three piece design like the Miata guys do with two smaller 'triangle' pieces to create a straight line across the rearmost edge of the trunk and a large, curved-top piece that articulates for tuning the angle across that back edge. I should be doing more mockup work this weekend and I'll post pictures of my cardboard if I get a chance!
I have managed to make a template and cut the Lexan for my DSP legal autocross spoiler. It fits really well considering I cut it all myself and was working from a paper template that I put together without a second set of hands. It attaches to the rear of the decklid and basically follows that angle(the part that tilts backwards at the top) up via some 1/4"-20 stainless machine screws that are threaded into aluminum Rivnut inserts that I installed in the back of the trunk, six in total.
Here is a picture of the Lexan once I got it cut, all of the protective film is still on it until I get all the mounting finalized:
Spoiler cut out of polycarbonate
Here you can see the spoiler on the car, first picture only has the two inner screws in it so it isn't following the curvature of the trunk but the second one shows it all bolted up:
Giant spoiler and helpful girlfriend
Front view
As you can see, this spoiler is freakin' huge. 10" from the bodywork is the limit in DSP and I decided to go for the largest first and I will modify it if needed. I am currently waiting on delivery of two Longacre spoiler support turnbuckles to finish the install. The spoiler is very sturdy through the middle where the curvature acts as a brace of sorts but the two outer corners are not very rigid and driving with it on would definitely put a decent bit of load on the mounting bolts. The two turnbuckles will be attached to the outer corners and utilize the forward mounting holes from the OEM spoiler unless the angle doesn't seem to be enough in which case I will drill new holes for it.
The angle of attack may seem absurd but from my research the angle has very little effect in autocross and near vertical is fine since overcoming the drag won't be an issue at the speeds typical. The spoiler is there to stabilize the car basically by creating drag through the fast corners and slaloms so that the suspension and alignment can be set up for the slow parts of the course without creating an undrivable car in the fast parts.
I will post more pictures once it is truly finished and next on the list is making a splitter to match. Let me know what you think or if you have any ideas for either!
Here is the final installment of the rear aero saga!
As you can see the fitment worked out pretty well! I was able to repurpose the front holes from the stock spoiler to bolt the support rods into, I could(should have) ordered one size down on the turnbuckles but they will work and it's not worth the money/hassle to change them over. Since I can't put much preload on the spoiler with them it flutters at higher speeds a bit, we'll see if that becomes an issue. It held on for a 70+mph highway run with no ill effects so I am going to say the mounting was a success!
Next step, front aero. I pulled it all apart this weekend and got ideas of how I'm going to mount it all, just gotta find the material I want and get cutting!
Please post video of this thing flapping in the wind.
I'll make sure to get a good angle at the event next weekend.
I think you'll be surprised with the rigidity, I originally planned on putting more supports but after mocking it up the first time realized that the curvature of the trunk provided a lot of stiffness on its own.
Anything else? I guess I should post up my own Aero Mods.
I had an issue where I was getting some rear end float while cornering over 100mph, especially when getting up to 110mph through the roval at CA Speedway or turn 8 at Willow Springs. By installing a subtle rear spoiler and cutting out the fake mesh stuff in the rear bumper, this has been resolved.
Thanks! I'm building the car for NASA's new class, ST4 which can also run the Time Trial class TT4. We're limited to how far the splitter can extend from the body by 4" (at point of intersection w/body). The splitter also has to be flat and horizontal, so we can't develop anything more sophisticated. The idea is that this keeps costs down and makes the class more inviting to a broader range of people.
We're also not allowed to do anything inside the wheelbase. So no side-skirts, no flat floor, no barge boards, nada. Out back, no diffusers are allowed, though we are allowed to remove as much of the rear bumper fascia as we want so long as it still covers the bumper support bar (so the silly exhaust trim panel has got to go). We are allowed a rear spoiler or wing, but there are some modest limits on the size and placement of those as well. I'm going with a wing (APR GTC 200).
