2019 MAZDA ROADSTER MX-5
The updated, 181 horsepower, 2.0 liter SkyActiv-G (MAZDA)
the engine is getting a bump to 181 horsepower and this is achieved through a variety of changes. The first and most exciting is that retuning has allowed the redline to be increased from 6800 RPM to 7500 RPM. According to Car Watch, the first modification to support the engine spinning so much higher is an increase in the rate of the valve springs to provide more tension. The pistons have also been lightened by 27 grams by shaving down the dome and getting the valve reliefs as close to the edges of the piston skirts as possible.
The connecting rods get a similar treatment, losing 41 grams of weight due to a more compact shape along with bolts that are shorter and thinner. The crankshaft gets some optimization in the form of how the counterweights are arranged. The changes continue on with the throttle body which sees its opening increased by 28 percent in order to provide more air to the engine. The airflow changes continue down towards the valve with improvement in tumble flow and an increased valve diameter.
Hashimoto Yohei of Car Watch states the changes in the exhaust are apparent as soon as the car is started describes the pull to 7500 RPM as exhilarating. He also states that the new redline allows the car to be wound out a bit more. That prevents upshifts that would have been required in the past and the Miata gets up to speed more quickly.