1994 Mazda MX-5 Miata - Dark Diggler

If there's one thing Mazda's Miata needs, it's boost. Sure, Mazda announced its factory turbo Miata just a few short months ago, but there's a decade-and-a-half's worth of Miatas already on the road, crying for some ponies. Enthusiasts knew from the start that the Miata's thrashy normally aspirated iron-blocked four-cylinder had its roots in the turbocharged 323GTX. To power-hungry Miata loons, cramming copious quantities of pressurized air down its gullet was a no-brainer.

First, it was supercharger kits. Simple, low-boost non-intercooled roots blowers with rudimentary fuel controls sprang up, followed by a small variety of turbo kits with somewhat better engine controls.

At the time, though, none of the aftermarket forced-induction options available for the Miata sated Jason Kavanagh's boost jones. For him, there was either not enough power, or the safety margin was too questionable, or both. Compromise was part-and-parcel in the Miata kits of the day, so in 1997 he decided to go the custom route for his black 1994 A-package Miata to turn it into a daily-driven track day sleeper. Particular attention was paid to thermal management, as overheating is a bugaboo of Miatas, especially track-flogged ones with briefcase-sized intercoolers blocking the radiator.

The first order of business was the turbo. Being an engineer at Garrett Engine Boosting Systems, Kavanagh whipped up a unique turbocharger that eventually spawned Garrett's GT28RS turbo, aka Disco Potato. The main differences are that his turbo uses a prototype high-efficiency compressor stage and an extrude-honed turbine housing. The remaining bits of this hybrid are found in the production GT28RS: the ball-bearing cartridge, the high-flow 76 trim NS111 turbine wheel and the 0.86 a/r turbine housing.

Coupled with a beautiful tubular header with equal-length primaries made of 321 stainless steel, boost response of this turbo is outstanding-according to the owner, it hits 12 psi of boost at 2900 rpm on the totally stock 1.8-liter engine; remarkable considering the GT28RS' 300-whp capability. A 35mm TiAl wastegate is grafted onto the merge collector of the header, and the wastegate flow is plumbed back into the 3-inch stainless downpipe about 16 inches downstream of the turbine discharge. A 3-inch high-flow cat keeps tailpipe nasties to a minimum. Who says high performance means dirty air? Before being belched into the atmosphere, the exhaust passes through a 3-inch straight-through Borla XR-1 muffler. The tone is mellow and blat-free, with a deep burble at idle and a full-lunged roar at speed.

A modified airbox from a Bell Engineering kit feeds the turbo's compressor through a custom 2-inch aluminum inlet pipe, while 2-inch aluminum intercooler plumbing leads to and from a colossal 18x12x3.5 Garrett bar-plate intercooler core via custom sheetmetal endtanks. Amazingly, this intercooler fits in the car's "mouth" without any modification to the chassis. An HKS Racing bypass valve vents to atmosphere, though Kavanagh isn't totally satisfied with its ability to prevent compressor surge in his application. He's got a stock 1g DSM blow-off valve ready to take its place.

This beastie hasn't seen any dyno tuning to date. The conservative street-tuned calibration has yielded a car plenty quick, even for powerbroker Kavanagh, whom today heads Garrett's aftermarket engineering activities. You see, aside from power potential, the benefit of a highly efficient turbo system is that it minimizes exhaust backpressure, easing the load on the car's cooling system. This thermally conscious approach holds true to the original goals of the project.

Likewise, the stock radiator and fans were swapped for a Flyin' Miata race radiator and a pair of Spal 11-inch fans that suck hard enough to make Paris Hilton blush. These fans draw so much current that an independent electrical circuit was deemed necessary, complete with new relays, fuses and heavy-gauge wiring. To prevent cooling air from bypassing the intercooler and radiator, Kavanagh fabricated an air inlet guide from aluminum sheetmetal and weatherstripped the whole works. As a result of all these efforts, no overheating has been encountered, even in high-desert track conditions, although oil temperatures will climb during extended track sessions. A remote oil cooler is in the cards.

The key ingredient to safe, consistent operation of engines functioning on the knock threshold lies in the engine controller. Here, an Electromotive TEC-II is wired in parallel with the stock Miata ECU. It's an unusual technique, but the advantage is that it allows the two engine controllers to manage what they each do best. Fuel and spark control are handled by the TEC, while the stock ECU continues to operate workaday chores like fan switching, charcoal canister purge, fuel pump control, idle control, EGR, and hot-start fuel pressure. Injectors are low-impedance RC Engineering 550cc/min units plumbed by a dual-feed Vishnu fuel rail and a Walbro GSS342 high-flow fuel pump. Kavanagh and Shiv Pathak of Vishnu Tuning tuned the whole works.

Suspension enhancements are relatively straightforward, with Ground Control coil-overs and Koni adjustable shocks all around. Tires are sticky 205/50-15 Falken Azenis on gunmetal 15x6.5-inch Rota Slipstreams. Since he hasn't found a big brake kit he's satisfied with, the brakes are essentially stock, with Goodridge stainless lines, Porterfield R4 pads and high-temp Motul 600 fluid.

In the cockpit, you won't find any whiz-bang stereos or garish colors. Everything follows the dead-serious, no-bullshit motif. A double-diagonal Hard Dog Hard Core roll bar virtually disappears from view when the top is raised. Other changes are equally subtle, including the addition of a shift knob from a '99 Miata, an A-pillar coolant temp gauge and a dash-mounted gauge pod. The latter was custom fabricated in hand-formed aluminum sheet metal and finished in flat-black wrinkle-finish paint to cut glare and for a classy, unobtrusive appearance. The pod follows the contours of the dashboard and houses three Auto Meter gauges: oil temperature, boost and exhaust gas temperature.

It's when you drop the throttle in any gear that you feel like you've been rear-ended by a locomotive. Even in fifth gear, the rev limiter comes up in a shockingly short period of time. Yeah, it's uncompromised, all right-uncompromised license-liquifying ability.