The team doesn't have the resources to test its aero package in the wind tunnel, so they rely on good old fashioned track time to tell them what's working and what isn't. Recently, they realized that the Top Fuel-type wing they were using wasn't creating enough downforce on the rear tires at the speeds they were hitting. "Maybe it might have made a difference at 220 or 230, but not at 205," Tanaka said. So they swapped it out for a Pro Stock-style wing that creates "little drag, lots of downforce, and is adjustable for track conditions. Simpler is sometimes better."
Tyler also said some of the team's aero work is done for reasons other than downforce and drag. Holes in the hood-more properly called NACA ducts-feed air directly into the custom T-Series turbochargers. The design of the flush-mount NACA ducts allows air to drop into the duct without interrupting the flow of air around it, like a hood scoop would.
The Rocket Science of Antony Kim
You may not know his name, but we bet you're familiar with some of the cars Antony Kim has helped to design. An aerospace engineer specializing in race car aerodynamics, Antony brought new levels of airflow control to Steph Papadakis' latest Civic drag car. His work resulted in a car that was not only faster, but also considerably more stable, so much so that Papadakis refuses to drive the old car anymore.
His approach is to create considerable downforce on the front of a a FWD car is to "defy gravity," as he puts it. During a hard launch, much of a car's weight transfers to the rear, which is not good if you want to plant a FWD car's tires for maximum traction. So Antony is upping the downforce on the car's nose. But he has to achieve a balance and keep some downforce on the rear, he says, or the car won't be stable and could come around whenever the driver lets off the throttle.
When we asked Antony if any of his drag-race aero lessons could be used on street cars, his reply surprised us. "Not at all. The forces acting on a drag race car are completely different than a street car. Plus, I'm working on a car with a 75/25 weight distribution, which will never happen on a street car. If you're going to mimic anything, follow a road race car," since it has to do more than just go fast in a straight line.
Antony's tips for improving street car aerodynamics have more to do with air flowing under the car than over it. "Number one: Lower the car. The lower you can make it, the more downforce it creates. Two: Mount an air dam or chin spoiler. This will prevent air from going under the car and getting turbulent when it hits all those protrusions underneath the car. Three: Run the lowest side skirts you can, to seal the sides. This will make the car more stable.
"And remember," he continued, "every little thing you change on the car has an effect on the rest of the car. What you change in front is going to affect the back."
Wind Tunnel-Tested
We found only one company-Mugen-that performs wind tunnel tests on fullsize models of its aerodynamic parts. APR Performance does some testing, but only on quarter-scale models. Mugen starts with the quarter-scale pieces during development work, but eventually tests the parts in 1:1 scale at the Japan Automobile Research Institute in Tsukuba, Japan.
What's so special about wind tunnel testing? It allows a manufacturer to evaluate its aero designs under very controlled and repeatable conditions, resulting in body kit parts that are proven effective at reducing drag and improving downforce. For example, the kit Mugen developed for the RSX, when combined with a lowered suspension and smaller mirrors, increased the car's overall downforce by 168 percent (at 60 mph), and decreased its CD by 11 percent.
The wind tunnel can reveal problems, too, admitted Scott Zellner, president and CEO of King Motorsports, the exclusive U.S. distributor for Mugen. For example, Mugen spent some $20,000 in research and development to design a rear diffuser for an S2000. But during repeated tests they found "they just couldn't make it work," Scott said. So Mugen scrapped the project.