CorkSport continues to strive for new and innovative products to elevate the Mazdaspeed platform, even as many in the community have fallen away from it. For the past year, we’ve been steadily working on a throttle body upgrade for the DISI MZR that doesn’t force you to compromise between performance and drivability.
Our initial design process started with simulating various inner diameter sizes to see where maximum gains could be achieved with both 2.5-inch and 3-inch IC piping. The resulting best compromise for both piping was 72mm ID versus the OE 60mm ID. The 72mm ID also allowed us to retain the OE bolt pattern for a painless installation utilizing an O-ring for sealing between the throttle body and intake manifold.
Once the prototype was produced, we began the validation process. To prove and measure the true increase in airflow, we flow-benched both the OE and CorkSport throttle bodies. To reduce variables in testing, both throttle bodies were equipped with 3D-printed velocity stacks with a 0.5-inch radius.
The flow bench testing showed impressive gains at 28-inch H20 with a 12mm larger ID. Testing was performed at 25 percent, 50 percent, and 75 percent throttle plate open. We attempted 100 percent, but the flow bench we used could not support that high an airflow. At 75 percent throttle open there was an increase of 131cfm.
With the flow bench showing impressive improvements, it was time to put it on a car and see how it responded. Installation was straightforward, only requiring a new 3-inch silicone couple and T-bolt clamp. The first drive with the new 72mm throttle body was quite undramatic — I consider this a great thing because the car drove great. There were no odd throttle surges, no choppiness, and no unpredictability. Throttle response felt a bit more crisp and alert in a predictable way.
The first dyno testing was performed on a CorkSport turbo-equipped car with CorkSport camshafts and intake manifold. Dyno testing showed about 100rpm decrease in spool and inconclusive peak power gains. This may be due to the lower volume of airflow moving through the engine. However, driving the car felt better.
Next, we wanted to see how the 72mm throttle body would react with a larger turbo setup. We sent the prototype to a beta tester running a GT3582R at 34psi with a built and PI-equipped engine. This is where the CorkSport throttle body woke up. Check out the graph below. The green graph represents the OE throttle body, and the blue graph represents the CorkSport prototype 72mm throttle body.
Again, the results are impressive with a 16wHp/20wTq increase at peak power, but what’s even more impressive is the power under the curve. There are consistent gains from spool to redline. Spool was about 100rpm sooner, followed by a substantial gain from 4,000rpm to 5,000rpm and more conservative gains from 5,000rpm to redline. Both of these dynographs were produced on the same day within a few hours of each other due to the installation time.