After the engine was installed, a custom Corky Bell turbo kit was fabricated for the Miata. The turbo kit is a one-off custom kit that Stephens designed himself using custom parts. The cast turbo manifold is a Corky Bell unit, which has been reworked by Stephens to achieve better flow characteristics. Mounted to the manifold is a custom turbocharger.com T4/T3 hybrid hairdryer capable of producing more than 25 psi of atmospheric pressure. An HKS EVC IV boost controller and Corky Bell wastegate handle boost control duties. From the turbo, spent gases are expelled from the turbo housing via a custom Thunder Fabrication 3-inch downpipe exiting through a 3-inch Ultra Flow canister. On the compressor side, boost pressure is routed through 2 1/2-inch mild-steel I/C piping to a custom Corky Bell front-mount intercooler. After ample chilling, the charge air is then force fed into the port-matched intake manifold.
Once the charge air enters the combustion chamber, 550cc squirters from RC Engineering inject high-octane juice to the mix. Ensuring all injectors receive their fair share of juice, a high-flow in-tank pump transfers fuel from the tank to a custom Vishnu high-flow fuel rail. Factory bumpsticks orchestrate valvetrain operation. The 9.0:1 compression factory cast pistons then further compress the mixture in the chamber. As the compression stroke nears the end of its cycle, the NGK plugs ignite the mixture, causing a violent explosion to send the piston downward onto its power stroke.
Wanting to extract the full power potential from the turbo engine, Stephens realized the best method was to employ a complete stand-alone engine control unit. Wanting to use the direct-fire coil set-up originally found on the Miata, Stephens called upon Electromotive for a complete engine management system. Since Stephens was a novice when it comes to the Electromotive system, Fred at Electromotive recommended a TEC-II unit capable of controlling fuel and ignition maps. The unit also comes equipped with the high-energy direct-fire coil set-up that Stephens was searching for. Having never installed a TEC system before, Fred and fellow TEC and Miata owner Barry Birdwell helped Stephens through the installation phases. Once running, Birdwell gave Stephens a crash course in tuning, which was crucial in keeping the factory engine alive. With Birdwell's tips and help, Stephens was able to extract 399.4 hp and 375 lbs-ft of torque at 25 psi of boost pressure-all this from an internally stock factory 1.8-liter engine! Novice or not, 400 to the wheels is getting it done!
Stephens knew that making power out of the Miata was going to be the easy part, getting it to the ground through D.O.T.-approved drag radials would be a totally different story. Transferring the power from the crankshaft to the transmission is a factory 1.8-liter flywheel, which he chose for the larger surface area (215mm vs. 200mm 1.6-liter flywheel) to contain the harsh torque of clutch engagement. The clutch Stephens selected was an ACT unit using the company's Extreme pressure plate with a six-puck race disc. Knowing the factory driveline was the weak link, Stephens upgraded the factory driveshaft, rear-end and drive axles. Providing the tire patch are a pair of 225/50-15 BFGoodrich D.O.T. drag radials mounted on lightweight Enkei aluminum. Suspension travel was addressed with Tokico five-way adjustable Illumina shocks tag-teamed with stock springs allowing Stephens to set up the suspension to meet track conditions.
Although the Mazda is capable of clicking off 10-second e.t.s, Stephens noted that the Miata was built on a strict budget and remains fully streetable in its 10-second trim. Stephens spent $15,000 on his race Miata over a period of two years. Some might think this a lot of money, but the price tag also includes the car's purchase price. We know of some people who spend that much on just the engine and turbo combo alone. When we last spoke to Stephens, he said the stock engine is on its last leg and that he is going to build the engine for more power and totally redesign the turbo system. If you are looking for Miata power, you might want to check out his Web site at www.racingmazda.com. Street Class racers beware, because this Minimonster is on a rampage and you're in its path.