We drove and tested the car at 8 psi but Chen and his tuner, Je-Kin (Luke) Loke, claim it runs safely at 12 psi. In fact, on our dyno it made 236 hp and 202 lb-ft of torque at 8 psi. At 12 psi, the numbers are even more impressive (see accompanying dyno chart).
What does one have to do to Toyota's 1ZZ-FE engine to make 235 hp at the wheels? The answer is surprisingly simple. As we already mentioned, a custom NuFormz exhaust manifold, which is obviously designed to allow some degree of exhaust pulse tuning is coupled to a Garrett T28 turbocharger, which feeds intake air to the throttle body via a Spearco air-to-water intercooler. The intercooler uses a heat exchanger mounted near the bottom of the engine bay to cool water, which in turn cools the intake charge.
The engine's stock in-tank fuel pump and pressure regulator were scrapped in favor of a vacuum/boost referenced fuel pressure regulator and in-line fuel pump. Loke also built a return fuel line, which empties into the MR2's stock filler tube. (The 1ZZ-FE uses a dead-end fuel system in stock trim.) Additional fuel management is handled by a Split Second ARC2 air/fuel ratio calibrator, which allows for fuel map adjustments at any combination of engine speed and load. Split Second also provided its ESC1, which alters the MR2's stock oxygen sensor signal allowing for open-loop operation as soon as the engine sees boost. Larger fuel injectors from a Honda S2000 replace the stock injectors.
Additional electronics from APEXi include an AVC-R gear-specific boost controller, peak-hold boost gauge and the company's latest turbo timer. The AVC-R allows for user-selectable boost control in every gear-a useful component in managing wheelspin in traction-limited cars such as this.
Significant chassis enhancements were required to keep up with the increased power and grip improvements. A World Sport Damper system from APEXi was installed, as were multiple chassis braces from Toyota Racing Development. The APEXi system consists of height-adjustable coil-overs designed for street use. These chassis improvements combined allowed the MR2 to push the Sport Compact Car slalom record to an impressive 73.8 mph.
We've already established that Toyota's MR2 and Celica excel when it comes to braking tests, so it's no surprise the added grip of R-compound tires gave impressive results. With stock brake pads, the little roadster ground to a halt from 60 mph in a scant 107 feet-another SCC record-breaking performance. The addition of Project brake pads, which are in the car's near future, will likely shorten the distance even further.
All in all, this MR2 was very surprising. Its speed, handling and braking are among the best we've tested. The next time some top-down purist starts preaching the wonders of a power-deficient roadster, remind them about Chen's topless supercar. It's how God intended the roadster all along.