These Class A Performance carburetors are tuned and ready to go right out of the box. They're built for stroker motors that will give you good street manners, performance, and crisp throttle response. Street Performance carburetors start off with a 750 vacuum secondary QuickFuel Carburetor main base. The choke horn is cut and it comes with a K&N sub stack. This carburetor is great for a 350-360 engine. The Performance Plus carburetors have all of these features, including bullet metering blocks and custom jetting - good for a supped up 350 all the way to a 400 engine. The HP carburetor is a 750 vacuum secondary base carburetor with a HP main body, bullet metering plates, and custom jetting. It's good for a 383-409 engine. The 850 Street Version has all the same features as the 750 Street Series, except its jetted for 393-460 big block engines.