Lemons Aero Study: Star Wars Ecotec Miata

A guy recently contacted me on Facebook to ask my opinion on aero modifications for his Miata. Cameron and his team live in the Great Lakes area and race Lemons. Their Miata has a Star Wars theme, complete with R2D2 behind the seat, with a head that spins, too. The car has an Ecotec swap. Cool build, right?

My first response was to get an airdam and splitter, but the team had already done that. They ripped it off shoveling mud, so it’s not in the pic, but the team intends to put it back on. He was wondering about also adding a wing, and how much would that help?

My reply was that a wing would certainly help. From my aero tests at Watkins Glen, I know that a car with a wing will beat a car without a wing in just about any simulation I run. However, a wing with an open top or chop top is about 2.5x less effective than one with a hard top.

Cameron wanted to know what this would do for lap times at Gingerman, his home track. Luckily that track is in OptimumLap, and Cameron provided me with some data based on a recent race, and that their theoretical best lap was 1:46.65. What would happen if they added aero?

I have Miata models in OptimumLap, but nothing with an Ecotec, so I used Cameron’s dyno sheet to make a new model.

Next I input weight of the car, final drive ratio, and set the tire grip value to 1.15g. This is a bit higher than I use for 225 RS4s, but the point was to get data close to his best lap. I made some guesstimates at drag and lift. His car has a partial roof, so I’ll use my Chop Top data and fudge it slightly because he’s using a stock front end, and not an airdam. Call it .5 drag and .34 lift.

Based on all this data, the simulation shows a 1:47.10, which is reasonably close to what Cameron said was their theoretical best lap, and was in fact their actual fastest lap in the race. So let’s see what happens when I add the airdam, splitter, and wing that Cameron asked about. At this point I can use the data I have (I tested almost exactly the same setup), and Cd is .45 and Cl is -.53.

Standard	Airdam, splitter, wing
1:47.10	1:44.72.

So that’s 2.38 seconds faster using aero. Pretty substantial considering the wing isn’t going to work very efficiently with that janky top.

My advice was to extend the roofline and support it at the rear with the wing uprights. (While still allowing R2’s head to spin.) I sent him a crude drawing that looks like this: the red is the extended roofline, the blue is the wing and uprights.

The roof extension would provide clean air to the underside of the wing, which is what a wing wants. The roof mod might look silly, but this is Lemons where silly is de rigueur. With this modification he might arrive at values of something like Cd .45 and Cl 1.0. This would theoretically drop lap times by a full second.

Standard	Airdam, splitter, wing	Extended roof
1:47.10	1:44.72	1:43.63

OptimumLap assumes a perfect aero balance, but in the real world you can’t just keep adding rear aero and expect faster times. This is just a simulation, after all, but it’s good to know if the trouble and expense is worth it on a Lemons build like this. In this case, I’d say yeah.