If I didn’t have Miatas, I’d probably have a FRS/BRZ/GT86; similar philosophy, but in a coupe with better aero. My brother is thinking about a new car, and a 86 is on his list, so I thought I’d take this post out of the can and finish it. One of the reasons for owning this car would be to run it in the 86 Cup time trials, which seems like a cool series with a great rule set.
The 86 Cup rules has a Stock class, which allows you to take any modifications from an approved list. This is probably how I’d race one, but it doesn’t allow you to do much with aero. Since this is a website based on aero, let’s take a look at the aero options for the non-stock classes.
The rules allow you to modify the car, taking different amounts of points for each modification. The point total puts you into one of four different classes, which can result in different cars, with very individual builds. In the Street class, you’re allowed up to 4 points, in the Modified you get 7 points, and the Unlimited class is, well, unlimited.
|.25||Level 1 Front||Aftermarket bumper, no splitter|
|.75||Level 2 Front||Splitter, spats, canards, everything|
|.125||Front spats||Not unless you increase track|
|.25||Vented hood||Would help with splitter|
|.125||Fenders||Aftermarket or vented|
|.125||Cut rear bumper||Poor man’s diffuser|
|.25||Level 1 Diffuser||Starts behind rear axle|
|.5||Level 2 Diffuser||Starts in front of rear axle (but how far?)|
|0||Underbody panels||Any year OEM underbody panels|
|.125||Vortex generators||Please no|
|0||OEM spoiler||Any year OK|
|.25||Spoiler||Any non-OEM spoiler|
|1||Level 1 wing||Up to 55″ wide, 8″ stands|
|1.5||Level 2 wing||Up to 57.5″ wide, 10″ stands|
|1.75||Level 3 wing||Anything goes, I guess|
That’s a lot of options to choose from. How do I think they stack up?
The aftermarket has turned out some interesting BRZ/FRS bumpers, but without an undertray and splitter (and hood vents if you’re doing those), I’m not sure any of them are better than stock. I guess if you have .25 points lying around, then why not.
A better choice is a splitter, it costs .75 points, but then you can use any bumper you want, wheel spats, and canards as well! Data from my testing showed that a splitter is very worthwhile, and so I’d take this option with side spats and maybe canards.
If you study the YouTube videos from Kyle.Engineers, you’ll see that a diffuser doesn’t do that much unless you’re optimizing the underbody. That means first add a splitter, then side skirts, and then a flat bottom (or Venturi), and after all that, add a diffuser. Indeed, a flat bottom alone is superior to a diffuser, so I wouldn’t bother with a diffuser unless I’d done everything forward of that first, and still had points. Cutting the bumper also helps, but it’s such a negligible gain that I’d only do that if I had points to spare.
Spoilers and wings
The spoiler and wing options are interesting.
- A spoiler costs zero points for OEM and .25 points for anything else. I’ve got a pretty wild imagination when it comes to spoilers, and I’d probably make my own adjustable spoiler if I was in the Street class. With more points to spend, or unlimited, I’d jump right up to Level 3 wing
- There are two Level 1 wings that are whitelisted (SARD LSR and BRZ tS), and I’ve never seen the data on them. These might be a bargain, or a waste of points. From what I’ve seen, they need bigger end plates for sure.
- The level 2 wing can be 2.5” wider and mounted 2″ higher than Level 1. I don’t know how much that would change the performance, but .5 points seems like a lot to spend on a couple inches.
- If you need more rear downforce, Level 3 is obviously the way to go. It’s only .25 points more than a Level 2 wing, with no restrictions on width, height, or set-back distance. Go big.
A full aero package (level 2 front, hood and fender vents, level 2 diffuser, level 3 wing) is 3.5 points. That same number of points would also get you a Super 200 tire (A052, for example) on a 8.5″ wide wheel, or a built engine with forced induction.
It’s hard to say what would be the best build. On some tracks, power, on others, mechanical grip or aero. I wrote about that once before, and while some tracks favor one or the other, it would be difficult to modify your car between races. But it does appear that the 86 Cup rules strike a good balance, and it would take me a few hundred simulations to figure out which options I’d run. But at first blush the splitter and spoiler only cost 1 point, and seem like a good combo for a Street-class build.
Verus Engineering Aero Packages
Verus Engineering makes a lot of GT86 aero parts and if you dig around on their website you can find information packets, which gives you in-depth information on their aero parts. These informative packets also group some aero parts together in different “Ventus packages” that are supposed to work well together.
In a way I want to congratulate Verus on providing the customer such valuable data, but honestly… it borders on smoke and mirrors. The only thing I need is the drag and lift values, and after you wade through 29 pages of text, images, and tables, guess what they don’t give you? Drag and lift values.
It took a couple emails back and forth with their engineering department, but I finally got what I wanted. They claimed that drag and lift was confusing to most customers, so they no longer provide that. Well it’s not confusing to this customer, it’s the only two values I give a shit about.
Anyway, rant off, here’s how those Ventus Packages stack up.
- Ventus 1 – This package has canards (dive planes), underbody panels over the transmission and rear suspension, and a diffuser. It’s interesting that they chose to use canards, which are very inefficient, together with underbody aero, which is totally unrelated. This would be .625 points in the 86 Cup, and have Cd = 0.372, Cl = 0.013.
- Ventus 2 – This package adds a splitter and ducktail spoiler to the first package. People often think splitters and spoilers add drag, but here’s another case where you get more downforce and less drag. This would cost 1.25 points in the 86 Cup, with Cd = 0.355, Cl = -0.195.
- Ventus 3 – This package adds endplates on the splitter, side splitters (side skirts), and a high-efficiency rear wing. It’s interesting that they chose to use both a spoiler and a wing on this package, I guess you’d have to take both for points. It looks like a Level 2 wing, and so this package would cost 2.25 points, plus whatever side skirts cost (not listed in the 86 Cup rules). Cd = 0.441, Cl = -0.499
- Ventus 4 – This package exchanges the spoiler and high-efficiency wing for a bigger wing. Same 2.25 points as the Ventus 3 package, with Cd = 0.465, Cl = -0.633
Personally, I would not have done the packages in this way, because you’d get more benefit by going front to back. Meaning, do the splitter first, and the diffuser only after you’ve sealed up the sides and cleaned up the underbody. But Verus is trying to sell things to street-driving customers, and the splitter is not curb-friendly, and diffusers look cooler, so starting at the back makes financial sense. Likewise, canards are the last thing I’d do, but maybe the first thing a typical customer buys? Lame, but I guess it’s not what you can build, it’s what you can sell.
So you might be wondering which of those packages is fastest? Let’s run them through OptimumLap and find out. I usually factor in more drag and lift to simulate open windows, but this time I’ll use the Verus data as is. I’ve made the tire grip 1.2g across all configurations. I’ll simulate laps at Watkins Glen, NYST, and the 2010 Solo Nationals autocross track, to see what happens at different speeds.
Note that I’m a bit skeptical of Verus’s CFD values. The downforce (negative lift) is less than I’d expect. A GT86 with a splitter and a wing should be similar to my Miata with the same, which was measured at .41 drag and -1.2 coefficient of lift (with windows open, mind you). I don’t run a diffuser, flat bottom, canards, etc., and got way better values than Verus did. I don’t know why there’s this discrepancy, but anyway, I’ve added my car’s aero as the final entry in the table.
Based on OptimumLap simulations, the Ventus packages keep going faster as you add more of their doo-dads. This holds true at autocross and medium-speed tracks like NY Safety Track. However, at Watkins Glen, notice that the bone stock configuration actually went faster than Ventus 1, and the Ventus 2 package with a spoiler instead of a wing was the overall fastest. Watkins Glen is a fast track, and if you don’t have a lot of power, drag reduction is super important. Finally, the true potential of the aero packages might be closer to my car, which flat out stomps the CFD-generated numbers. YMMV.
After reading the rules and running some simulations, this is how I’d make a car for the 86 Cup.
Street class (4 points) – Splitter (.75), vented hood (.25), spoiler (.25), 9” wheels (1.25), GT Radial SX2 245/40-17 (-1). That’s 2 points, giving me 2 points for suspension or mild engine mods.
Modified class (7 points) – Splitter (.75), vented hood (.25), level 3 wing (1.75), 9” wheels (1.25), NT01 (1.0). Thats 5 points so far, and gives me 2 points for suspension or engine stuff.
Unlimited class (any) – All the aero, supercharger, wide tires and slicks, fully adjustable suspension, etc. I mean, duh, all of it.
Stock – (0 points) – But I’d probably race in the stock class, which allows front camber plates and camber bolts, rear lower control arms, oil cooler, cat-back exhaust, base trim spoiler, and updating/backdating to any OEM parts. I’d ride on 17×8 RPF1s with 225 SX2 and call it race ready. Sell my Miatas and get into this? Tempting.