After tracking a short list of Toyotas — an MR2, Lexus IS-F, and a GR86 came first — Marshal Moore decided on turning his teenage fantasy machine from an HPDE car into a Time Trial competitor. Of course, it was in the family.

After spending roughly the purchase price of his fourth-generation Supra on modifications, he had himself a forgiving car with power in spades and remarkable stopping power. Unlike so many examples of this slinky grand tourer, it’s far from the cumbersome freeway machine it’s come to be thought of.

However, the Supra is still near its factory weight, and despite its fat footprint, Moore figured he could improve the car’s aerodynamics to help its long nose turn more eagerly.

“It was understeer-y on the factory aero with a little stagger; 265s up front and 275s in the rear,” he explained. Following a frustrating trip to VIR, where the car would sidestep under crosswinds and slither under braking, he decided to stabilize the rear with an Esprit 651 wing. Unfortunately and all too predictably, that shifted the aero balance in the wrong direction.

Up until that point, Moore had been satisfied with the general balance of the car — it had been much more eager to turn than he had heard. He also had been committed to using only reputable Japanese parts whenever possible. To deal with the Supra’s pushiness, he scoured all the JDM auction sites for a neutralizing splitter. When that failed, he started seeking for a domestic alternative that would balance the aero load, even if it meant getting docked a few style points.

Because the fourth-gen Supra never made much of a broad splash stateside, there wasn’t an off-the-shelf splitter he could find online, so he sought the help of a paisan who could tailor something to the Toyota. One company wanted to fly their staff cross-country to scan Moore’s car — and that was not in the budget. Three strikes, no dice, and no real clue where to turn.

Then the name AJ Hartman Aero popped up in a road racing forum. He was pleased to learn Hartman had moved his shop from New Jersey to somewhere nearby, only a few hours from Wilmington, N.C., to South Boston, Va.

“I’d never had any requests for a Supra splitter before, but I liked the sound of it, so I agreed. Plus, I’d just bought a CNC machine and I needed a good reason to use it,” Hartman recalled.

Over the phone, the two discussed the general design, a few optional features, the time frame, and the price. Weight was paramount with the nose-heavy Supra, so Moore specified a complete carbon splitter — one without any fiberglass backing. He had to be able to quickly remove it in case he blew an intercooler pipe, so he requested quick releases. There had to be tunnels and endplates, too.

Supraration Anxiety

When the excitement of the planning ended, separation anxiety set in. Moore was already ambivalent about leaving his pricey pride and joy in a shop he’d never been to before, so it might have been better that no money was exchanged that day — that would happen when Moore collected the car a month later. “We wrote a few ideas down on a napkin and then I dropped my dream car off with a stranger, basically. I was a little nervous,” he admitted.

Aside from the Professional Awesome quick disconnects, Hartman designed the entire splitter assembly on his own. Since Hartman didn’t see the demand for a Supra splitter beyond Moore, he decided to take an antiquated approach to design — one more expedient for small-batch builds.

“I’ve been to a full scale wind tunnel with over a dozen cars before,” Hartman began, “so, for these small-scale projects, I can build them the old-fashioned way. It saves the customer money since I don’t have to bring CAD into it. I can put something at a 5” perimeter outline with cardboard-aided design faster than I can design a model.”

He can cut his own stuff by hand quite easily, too, and so, for this project, he decided to use the splitter blade instead of a computer.

When the scale increases, as it does for bread-and-butter cars, Hartman relies on CAD and CFD to optimize the design and automation to minimize the amount of cutting he’ll do himself. Without any stamina-related problems to hinder his progress, he can focus on quality control.

A cardboard cutout is all a talented aero designer needs.

A basic process suits some better than others, though. “Some customers even send me their own template cut from cardboard, plastic, or even construction paper; and others will send a CAD file. I then send them a carbon blade several weeks later and leave the mounting challenges to them.”

Moore’s splitter assembly was more involved, though. In addition to the blade, he wanted endplates, tunnels, mounting brackets, and an air dam. He relied on the  blade design he’s been using for the past five years, a solid piece of structural foam wholly contained by two pieces of carbon, which touch at the leading edge and reunite at the trailing edge.

The leading edge of the splitter sticks out five inches farther than the bumper, and the trailing edge of the splitter terminates in front of the crossmember, which hangs somewhat low. The reason the splitter wasn’t taken all the way back to the oil pan, which is sometimes the case, was because the right angle had to be achieved.

His splitters are always mounted at a slight rake, meaning the trailing edge sits a tad higher than the leading edge. The reason for this is to allow for a slightly larger volume of air at the rear. As the air flows from the constricted front area to the rear of the splitter, the air accelerates in an attempt to fill the larger space at the rear to equalize pressure across the pressure differential, creating downforce. To lengthen the splitter and mount it underneath the crossmember would make that angle shallower than ideal. Longer runway, but a lower angle of attack.

Splitter dimensions decided, the next order of business was deciding on a mounting strategy. The problem with the Supra Turbo is that its front is covered in coolers and all the associated piping. To build the custom quick-disconnect brackets within the confines, Hartman had to get a little creative.

There are some general rules he adheres to when eyeballing a splitter design. To maintain sufficient rigidity, the brackets cannot be mounted too close to the splitter’s edges, nor can they be too thin. Where the mounts are best situated varies from car to car, but he’s seen enough to know when something will bend like a diving board and when it will happily support the weight of a fully grown man.

To navigate the cluttered real estate around the coolers, he devised a set of trick brackets that mount to the sides of the radiator support on the vertical plane. These drop and move the mounting point forward just beneath the radiator core. The trailing edge of the mount is a simple L-bracket that the trailing edge of the blade sits on. The one product used in this package which Hartman did not design, the Professional Awesome quick disconnects, mount to the brackets.

Limited real estate required a compact, perfectly angled pair of mounts to facilitate safe splitter mounting around the coolers.

Tunnels came next, and a surprising amount of leftover space once they were finished. “I squeezed them in between the frame rails and the edges of the front tires pretty easily,” he said. In fact, in order to limit the tunnel size to 81 square inches as dictated by the class rules he had to chop the ends of the tunnels off.

The finishing touch was a small, simple, but nicely executed ribbon of carbon to ensure clean airflow across the front of the splitter and underneath the car. The Aeromagic style lip has a soft, rounded edge, and because it was the piece that mounted to the splitter, a natural opening emerged at the point where their respective faces met. To seal the small slit, Hartman cut a flat sheet of carbon thin enough to take a slight curve and bolted it to the bottom of the lip. Airdam complete, he could mount the four splitter rods to the front bumper, attach his decal, and give his customer the phone call he had been awaiting.

The Professional Awesome quick disconnects can be seen just behind the trailing ends of the splitter rods.

On-Track Analysis

A few weeks later, Moore could put the new splitter to the test. Carolina Motorsports Park features a lot of technical sections punctuated by long straights and a few corners with real pucker-factor. All the improvements to the front axle would serve the car well, particularly in the decreasing radius corners. He had been there before when the car was not equipped with any aerodynamic parts, and then it had exhibited some mild understeer exiting many of the slower corners at the track.

Immediately, Moore noticed the improvement in braking performance, and the additional weight transfer he could achieve in the heavier braking zones was smacking the splitter against the road.

Thankfully, Hartman’s factored this into his design, and so, underneath the splitter, on the other side of the points where the splitter rods penetrate the blade, he attached a set of scuff plates. Effectively large washers, these aluminum buttons are designed to be sacrificial. Unlike the titanium skid blocks so many use to protect their splitters, these are cheap.

This time, there was none of that normal laziness at corner entry and mid corner. The obvious urgency at turn-in gave Moore the confidence to lean on the front axle for longer than usual and seek more mid-corner speed than he had before. In fact, Moore raked the rear wing as much as possible, and, even then, it was still pointy enough to make him tread carefully in the fast stuff.

Where the newfound front grip was exploitable during this shakedown was in the medium-speed corners, namely the trio of tightening corners called The Carousel. The nose stuck beautifully throughout the long loading phase.

Eventually, he began to apply the throttle a little too quickly for the steering demand, which picked the nose up a little early and forcing the front into mild, manageable understeer. When the boost arrived, he found himself having to deal with a push-loose snap of oversteer. “That was my one ‘oh s#@t’ moment the whole weekend,” Moore said. Other than that, the car had edged progressively toward oversteer in every one of the second-gear corners.

With moderate understeer exchanged for moderate oversteer, the limiting factor was now the rear. Of course, a square setup, an aging Torsen LSD, and, now, with the splitter overpowering the rear wing, there would always be a little too much rotation.

However, the car still inspired confidence since it would follow Moore’s steering inputs better than it had before. Before his wastegate began to separate, Moore clocked his personal best of a 1:40.19 — 5 seconds faster than his previous best. 

Now he has to figure out the right solution to settle the rear. The Esprit wing cannot complement Hartman’s splitter, so Moore may need to find a larger element to fix to the hatch. Call it a surmountable problem.

Images courtesy of PolitiPixels, © John Fugate and AJ Hartman

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