Bulletproofing a Turbo Honda AP1 S2000 for Time Trial and Racing

When NASA Arizona competitor Jim Shepard raced in Spec Miata, he said he got tired of fixing bodywork. Spec Miata was not as inexpensive as he’d hoped. The bang-ups and close calls were getting to be too much for the man who had just gotten into racing.

The apple didn’t fall far from the tree. Two years earlier, Jim Shepard’s son Sean had introduced him to autocross, and their shared preferences in cars was obvious. Their innocent father-son bonding weekends quickly snowballed into Time Trial, which Jim entered with a new car.

He did just that. He bought a mint second-generation S2000, drove it home from California to Phoenix, and made the short list of necessary changes to turn it into a TT4-spec car that, for the most part, was a breeze to run.

A hardtop, a rollbar, a set of Ohlins coilovers, thicker sway bars, and a fixed-back seat were all that the team needed to become competitive in TT4. As thrilling as it was, his curiosity led him into wheel-to-wheel and the resulting body damage from his chosen category had him looking for an alternative soon. Upon returning to his old Honda, he found it lacking a little something  — not quite what it was before was exposed to the bliss that is racing. If he wanted to return to Time Trial and keep getting his kicks with his recently raised standards, he would need something quicker.

Well, the AP2 he had run TT with was too nice to cage, and besides, he had sold it to support his Spec Miata racing. After eyeing a C6 for some time, he had to admit the sentimental bond was too strong to break. If only there was a way to double the stock F-series output without driving himself insane.

When he came across a listing for a turbocharged AP1 S2000 with an advertised 460 horsepower, some of the necessary cooling bits, and an unforgettable price, he had to stop and consult with a few acquaintances who had gone the turbo route. “Some guys who ran in TTU and other TT classes said that the fear around turbocharging S2000s was unjustified,” he remembered.

Horses for Courses

Despite the encouraging words, Shepard knew enough to know that there was a difference between a few hot laps and a full race. Running TT3 would be one thing, but making this car quick enough for ST3 or faster would put a special set of demands on the car and powertrain that time attackers didn’t worry about. However, the asking price was about what the turbo kit alone cost, and those savings combined with the thought of nearly 500 horsepower in a 2,500-pound front-midship were too tempting to say no to.

But there was a catch. “It was terrible to drive – the KW suspension was way too soft. With the way the power came in, it was uncontrollable,” he recalled. The thing was a mess, but not cosmetically. The body and engine were fantastic — it just needed some love.

Buy Once, Cry Once

Shepard was willing to dig into his coffers if he could resolve all of the Honda’s woes in one fell swoop. A set of Stoptech C43/42 big brakes, Karcept swaybars, Feal 433 three-way coilovers, a Wisefab grip kit, and a Racetech containment seat gave him the tools to make the force-fed Honda a lot easier to live with. The Wisefab kit corrects the kinematic issues that S2000 drivers deal with when lowering the car, meaning roll center, bump steer, and camber gain are improved for better roll stiffness, handling, and grip.

Handing issues aside, the spiky power delivery also needed to be corrected if Shepard was to truly gel with the car. The shopping spree continued with an Emtron KV8 ECU, high-flow fuel pumps, 1000cc injectors, a flex sensor, and a series of class-specific tunes would help wrangle the peaky 2.0-liter.

“The boost came in with a wallop,” Shepard said of the kill-mode setting. The full 460 horsepower was way too much for him then, and ostensibly for the car, even with its suspension improvements and sticky Hoosier A7s slicks wrapping its WedsSport 17” x 10” wheels.

“I had to learn to be careful putting the power down at higher revs. It’s not a torquey motor like the K24, but once you’re around 6,500 rpm, you can’t just floor the thing everywhere. It is definitely traction-limited now in places the ST4 car never was.”

The urge to compete wheel-to-wheel with other wildcards pushed him toward ST2, but the car counts in that class in his region made him consider ST3, where he would be guaranteed a closer battle.

A Home for Headcases

These two classes brought power down to 355 (ST2) and 274 (ST3) average horsepower, respectively, and both maps were much easier to manage. “When you reach your average power target, the curve flattens. From 6,000 rpm to 8,800 rpm, the curve turns into a mesa,” he said.

Not only did the power come in progressively enough to keep the driven wheels underneath him, but the motor didn’t strain much from the heat once he’d made a few additions to keep things in check.

At first, full sessions at ST2 power initially pushed the needle into the red, but adding a thicker Ron Davis radiator and a Setrab 23-row oil cooler fixed that. In 77°F weather, the oil reached 239°F and water never got above 183°F over a 19-lap race.

As far as ducting was concerned, Shepard had to devise a wide-mouth enclosure for the radiator assembly, and replace the Trackspec louvers with a set from a company called Race Louvers. These are positioned a little farther toward the front of the engine bay, and they dip below the hoodline as well. The combination of better location, greater area, and some ramp effect taking place under the hood helps exhaust the air more effectively.

The last piece of the cooling puzzle was finding the right blend to satisfy the engine’s thirst and reduce the thermal output. “On E85, the car ran fine, aside from trying to start it on cold mornings, and I considered taking it to the 2024 NASA Championships, but the 13-gallon tank wouldn’t hold enough for the 45–minute race.

E85 brought the temps down, but shortened the car’s stamina due to its quicker burn rate. With a flex sensor in place, he tested ratios until he found a near 50-50 blend of E85 and 91 pump fuel, which provided the right combination of range and cooling.

Ford Knox

However, the rest of the drivetrain didn’t cope as well. After three weekends, the differential failed. In went another stock-style differential and that lasted two weekends. Stubbornly, he went to another shop for another stock-style limited-slip, but this one had sturdier internals. Even the fortified F20 went kaboom within a few weekends.

He had to accept the S2000 wasn’t made for this sort of grunt, but that didn’t make him wish he’d picked up a Corvette instead. “Those are more expensive to get into and the running costs tend to be higher,” he said in his defense. He was going to see this force-feeding business through.

Though he hoped he had already written the last of his big checks, he had to make another round of eye-watering purchases to handle the horsepower, or so he hoped. The boost was addictive, and he was willing to spend like a junkie to keep chasing that dragon.

He turned to Grannas Racing, a drag racing specialist, which, among other things, builds conversion kits to implant domestic driveline pieces into import cars. Grannas had a Ford 8.8” kit ready for him complete with everything except the driveshaft. The additional 25 pounds this piece added to the total was hardly considered after all the time he’d spent underneath the car in the last year.

The Ford 8.8” took the power for weeks until the CV joints on the driveshaft broke, and he replaced that with a steel driveshaft fitted with u-joints on both ends. With this fortified piece in place, the car functioned flawlessly for several months until the other OEM bit at the other end of the driveshaft broke.

As before, he remained stubborn at the first failure. In went another AP1 gear box, but regular driving on ST3 power destroyed fourth gear in a little over a year.

“I had a cooler fitted to that gearbox, and I doubt the transmission would’ve lasted half as long without it,” he admitted. Again, Shepard turned to Grannas and spent another hefty sum on a Tremec T56 kit, which included everything needed to successfully swap in a modern transmission made to handle a V8’s output.

Farewell to Flimsy

Hopefully, he’ll be done thinking about all these big-ticket items once the new transmission is in place. So far, he has fortified the once-flimsy S2000 enough to handle twice the power it was designed for.

“The time attack cars don’t have to run 20 consecutive laps at full speed,” he said, “but I’m confident my car can run all day. I haven’t regretted the build once. I knew that a Corvette would be more expensive to buy and maintain. Being lightweight, even if it means some weaker parts, reduces the consumable costs. In the long run, that’s made the difference.”

Getting the car into ST4-shape was easy, but the big step came when moving into ST3. Now that it has been sorted, Shepard believes the next move into ST2 will be relatively easy. “I’m going to turn the boost up and add more aero,” he said. “I’m not worried about drag. I’m just looking for more fun. Assuming we can grow the ST2 class around here, I’m sure I’ll find it.”