The solid motor mount inserts reduce the flex in the motor mounts. What it basically does is send more power to the wheels than throughout the chasis. The regular OEM mounts are meant to flex to a certain extent to reduce vibration and improve overall comfort in driving. The only negative thing the mounts do (and to some it's a positive) is add a little more cabin noise and vibration. What the drive will notice when driving is that the car will pull harder, and there is less hesitation when accelerating. The Turbo guys are knocking off several tenths in their 1/4 mile runs with the inserts.
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