The 300-604 is the plenum top in the 300-621 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 lower overall height to fit under a stock or mildly modified hood in the front-feed configuration. The 300-621 Lo-Ram front-feed plenum entry was configured to provide a very low profile modular intake manifold suitable for turbocharged or centrifugally supercharged engines. 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.

Features:
Individual plenum top for 300-621 allows you to select your components individually as you build your intake system
Designed for GM LS Gen III and IV engines equipped with GM LS1/2/6 (cathedral port) cylinder heads
Designed for forced induction (supercharged or turbocharged) engine applications with peak power at 7000-8000 rpm depending on the application
Modular design allowing the use of the included front-feed plenum entry
Intake design facilitates custom inlet duct and throttle body placement
Low height to fit under a stock or mildly modified hood in the front-feed configuration
Front entry plenum flange allows design & fabrication of special throttle body adapters or inlet ducts for custom installations
Clears 1998-2002 (4th Gen) Camaro/Firebird and 1997-2004 (C5) Corvette cowls and hoods without modification
High volume fuel rails and mounting hardware included with ¾”-16 o-ring ports (8 AN)