Originally Posted by BonneMeMN
Rubber does not flex like silicone. Silicone is there to give way to torquing of the engine, and the movements of the airbox/induction.
Basically it gives, instead of making a solid hookup.
Time to bump this. It'* a serious concern for the L27 and L36 with the plastic intake, as when the motor flexes, the filter could hit the top of the underside of the hood insulator, and go no further. The rubber coupler from Home Depot would exert all that force to the TB mounting flange on the plastic UIM, stressing it. Use a silicone reducer.
The L67 cars don't have as much to worry about, but it'* still something to do RIGHT the first time:
That'* a good visible example of what I'm talking about. The car is in gear (D), foot on brake, 3000 rpms, and no broken motor or trans mounts.