The new Edelbrock “Thunder Series” AVS (Air Valve Secondary) are a leap ahead in carb performance. With the new “Qwik-Tune” adjustable secondary air valve, you can fine-tune the opening rate to match your engine's requirements. You can delay or speed-up the opening with just an adjustment without having to change any parts. Another outstanding feature is the dual-fuel inlet capability that helps prevent fuel starvation in corners and on hard launches. The front of the Thunder carbs have been CNC-machined and the throttle lever and adjustment hardware have black accents for a new, distinctive appearance. These powerful and dependable carbs are available in a 650 and 800 CFM capacity. Also available with Edelbrock's chrome-like "EnduraShine" finish. The perfect way to "top off" your engine! Square-bore, non-EGR.