While most of the differential movement is restrained by the stock Power Plant Frame, stiffer side bushings can also help cut down on it. This means your shifter moves less and more power is transmitted through to the wheels. It'll also help you avoid the classic 2-5 shift.
These Mazda Competition parts are about 40% stiffer than stock. They'll increase NVH slightly, but not as dramatically as solid mounts or polyurethane ones.
Fits all NA and NB Miatas. Sold individually, there are two needed per car.