Uprated Engine and Gearbox Mounts
Most vehicle are fitted with engine and gearbox mounts designed to insulate the cabin from noise and vibration produced by mechanical components. They do this by attaching the gearbox and engine to the cars chassis via rubber. The rubber used is designed primarily to insulate the car and is therefore generally quite a soft compound with a high degree of movement. As the rubber ages and it gets softer.
The movement allowed by this soft rubber is ok for a car driven gently but when you start pressing on and are more aggressive with throttle, braking and gear changes then the mounts can no longer support the engine and box properly. The rubber allows movement to the point where the car can start shunting slightly as the mass is no longer controlled and held in one position. There are a range of aftermarket mounts available, a lot of which are designed for race use and as such completely sacrifice any degree of civility in the hunt to eliminate all engine movement. This is great for a race car but if you drive a road car then this mounting system is too extreme for the majority of drivers.
Hardrace Engine Mounts
The Hardrace engine and gearbox mounts are designed to reduce engine and gearbox movement to an absolute minimum whilst still isolating the cabin from excessive noise and vibration. Although they are not as stiff as some rigid mounts they are more than good enough for the vast majority of road and race cars in eliminating drivetrain shunt.