Firewall block off kit removing the fan/defrost assembly is a standard modification on any lightweight 911 that is to be used for performance driving on or off the track. The only downside to this removal is that you are now left with holes in the firewall that are required to be filled for most organized track events. Rennline s block off kit comes with 5 specifically cut and formed shapes that allow you to plug these irregularly shaped holes in a matter of minutes. Anodized aluminum, stainless steel hardware included.