This insert is made in our softest Red 65A durometer material, specifically for Diesel models, helping to limit NVH transmission. Designed to fill the voiding in the OE rubber mount, it smooths out gear changes and throttle application by stiffening and supporting the often perished rubber, a common failure on tuned vehicles. This provides a more precise and settled engine response during acceleration and deceleration. A small increase in NVH, typically at idle, should be expected when stiffening the connecting mount between the engine/transmission and chassis. The harder the material used, the greater the NVH transmitted.