420a EGR block off kits let you remove the EGR valve easily. As some may know EGR valves make your intake filthy plus they recirculate those hot exhaust gasses back into your intake manifold... Thats a BIG NO NO because cooler air = more power and if your like us we like to squeeze as much power as possible outta these engines. . It has been said there may be a slight hp gain from this Mod.. but very little if any 1-2 hp