While the Tri-Point bolt-on turbo kit puts down a hair more peak power, the Mazdaspeed3's low-end torque, sophisticated electronic controls, LSD and torque-limiting boost-by-gear settings should still result in higher exit speeds out of Buttonwillow's many tight corners. We were only partly right. The Mazdaspeed3 has better immediate acceleration out of the turn, but the advantage of grip, higher cornering speeds, gearing and a wide, constant powerband that stretches all the way to rev-cut allows the Tri-Point car to more than make up for the difference.
In the corners, the taller five-speed transmission, now assisted by nearly double the power of the stock Mazda3, really shines. While not having the Mazdaspeed3's 2500rpm fifth-gear grunt, this turbo system pulls hard from the mid-range all the way to redline. The turbo-to-engine match and seamless power delivery is awesome, even in transient response. The taller gearing makes the revs ideal for the Buttonhook hairpin and the useable power up top helps the Tri-Point car attain nearly the same exit speed as the Mazdaspeed3, despite not having a limited-slip diff.
In terms of track performance, the Garrett GT ball-bearing turbo is a superior match for the MZR engine, with only a slight hint of 'planned' delay in the onset of power, coming in less than 500rpm higher than the near-instantaneous spooling of the Mazdaspeed3's turbo. Power delivery is also smooth and incremental, while the shift in the powerband is more favorable for track use.
Floor the throttle near the apex and boost builds just enough to start accelerating as you begin to unwind the wheel. From there, the Tri-Point car continues to accelerate through the higher gears right up to redline without running short of steam, making the final 1000rpm useful. Tri-Point's turbocharger makes power at a lower boost level while having much better and more usable mid-to-top-end grunt.
The time it takes to build boost and deliver predictable power also eliminates much of the torque steer. Any wheel spin is easily compensated for with mild throttle adjustments. Not many big-power front-drivers are this easy to modulate. Tri-Point also discovered that by adding a larger rear anti-roll bar (which helps keep the front tires planted when turning and accelerating), excessive torque steer and wheel spin can be tamed even further.
We were on the fence with our street impressions of the Tri-Point turbo Mazda3's suspension package consisting of slightly higher-rate lowering springs and adjustable Koni dampers. The setup seemed to lack sufficient rear travel and had an uncomfortable feel at high piston speeds, so expectations for its track chops were low.
We were wrong. The dampers, springs and Tri-Point-designed rear anti-roll bar work a lot better on Buttonwillow's slightly smoother pavement than on the street. Ride characteristics on track are similar to the Mazdaspeed3, but with a little less body roll. The added rebound in the Konis controlled the roll a little better while improving stability during high-speed transitions. The larger rear anti-roll bar improves turn-in, which feels more positive and responsive, as well as making the car easier to rotate mid-corner. This setup is a little more aggressive and neutral than the factory without overpowering the street tires.
The wider Bridgestone RE760 Sports (225 width, compared to the Mazdaspeed 3's 215 and the Mazda3's 205) also contribute to this vehicle's healthy exit speed, since mid-corner speeds are higher overall by virtue of the added grip. It's not apples to apples, but the RE760 Sport (which reflects what tuners would use on the street) is designed as a sporty replacement with less stick than the factory-supplied RE050A tire that comes on the Mazdaspeed3. With fresh rubber, we think the Mazdaspeed3 could have made up the one-second advantage the Tri-Point turbo Mazda3 posted with its lap time of 2:08.016, an amazing feat considering the Mazdaspeed3's on-paper advantage.