The Holley LS1/2/6 Lo-Ram intake manifold kits are designed for GM LS Gen III and IV engines equipped with GM LS1/2/6 (cathedral port) cylinder heads. These intake manifold and rail kits will work with OE (Original Equipment) or aftermarket cylinder heads. The 300-600 is the lower manifold in the 300-620 complete kit. Offering this separately allows you to select your components individually as you build your system. The Lo-Ram intake manifolds are designed for forced induction (supercharged or turbocharged) engine applications and the 105 mm throttle body part number 112-581 or similar models. The base intake manifold is designed with a low height to aid the packaging of a plenum mounted air-to-water intercooler in a top-feed configuration. The short runner, low-profile base intake manifold intended for forced induction applications was conceived to package with an air to water plenum mounted intercooler with a shorter overall height than possible with other existing intake manifolds. The fuel rail kits come with two sets of brackets. A set for long (usually standard length) fuel injectors and a set for short (such as Pico, or LS7) fuel injectors.