Naoyuki Sakamoto gives C/D the details on everything from engine design to chassis welds on the new hot hatch—and laughs out loud at the idea this car’s AWD and a RAV4’s have anything in common.
At the reveal of the 2023 Toyota GR Corolla, we grabbed a few minutes with Toyota’s chief engineer on the project, Naoyuki Sakamoto, to dig into some of the challenges in developing the car, and what he thinks makes it so capable on track.
C/D: Everyone here in the States was so jealous of the Yaris GR. How soon after Yaris did the team start the GR Corolla?
NS: Actually, we started to develop the GR Corolla in 2018. So before Yaris, we were working on it. I’d say almost the same time we are developing both cars.
The GR Corolla uses a three-cylinder engine. Was that designed for Yaris and adapted, or planned for Corolla originally?
The Corolla is using the Yaris engine, but to bring it to the U.S. market we thought we’d need more power, so we started modifications to make that possible. Americans demand power.
We are like that. If horsepower was a goal, why stick with the three-cylinder? Wouldn’t it have been easier to turbocharge a four cylinder?
Actually, the compact engine is right for a sports car. The more you can keep heavy parts close to the center of gravity, the better it handles, so a lighter engine is better. A lighter car is better.
What does the Circuit Edition weigh?
So to make more power, what did you do? You didn’t bore or stroke it, it’s the same size as the Yaris’s engine, but what, 30 more horses? And a three-cylinder needs a balance shaft, right? And this is twin-cam?
Yeah, 300, up from 268 hp. We increased the boost, and to do that, we needed to reduce the backpressure. We needed to move more fuel in, more exhaust gas out, and it creates a high backpressure. And yes, a balance shaft, and twin-cam, of course.
How do you keep everything cool?
We did so much testing on track, in summer, in winter. We opened up the grille, you can see, it’s huge compared to a stock Corolla. Vents to direct air through. Even the intake, we have a thin intake for slow speed, to move air through quickly, and another duct below that opens at higher rpm, to bring more air into the engine.
Is the whole chassis and body different than a stock Corolla?
The chassis is reinforced, 349 more welds and 2.7 meters more sealant, more glue. The floor is different in the back from stock, to make room for the differential. We also moved the battery from front to back for better weight distribution. The front fenders are one piece, the back extensions are bolt-on. The carbon roof is only for GR. The doors are the same as a stock car. The suspension geometry for the front uses a new connecting point, 15 mm higher to make the roll center higher, and we made it stiffer but also lighter, just in the design.
And the GR-Four, the AWD, is that a performance version of what a customer would get in say, a RAV4?
[NS laughs and brings over the AWD specialist, who also laughs]. It’s the GR system that is unique to this vehicle here in the States. It’s developed through racing, from our rally series. It’s going to offer a lot of acceleration control in different conditions.
Was the choice to use forged carbon fiber for the roof rather than a woven carbon because it keeps the price down, or because it’s stylish and new?
You tired of talking about this car yet?
No! I’m excited about it. We built it with a lot of passion.