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Holley EFI


Dual Injector manifold and fuel rails

Part # 300-603
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The Holley LS1/2/6 Ultra 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 300-603(satin) & 300-603BK(black) base-lower intake manifold provides two injectors per cylinder for hi-volume fuel demands, flexible fuel supply strategies, and dual-fuel capability. Offering this base intake manifold with fuels rails separately allows you to select your components individually as you build your induction system. Complete front-feed manifold kits are also available with dual fuel injectors, see P/N's 300-625 & 300-625BK. The front-feed, short runner, low-profile base intake manifold was conceived to package with high-boost turbocharged or supercharged induction systems with a short overall height not possible with other existing intake manifolds. The Holley Lo-Ram complete intake manifold kits and throttle body adapters available as a machined casting 300-606 & 300-606BK are configured for a 105mm throttle body, see Holley P/N 112-581 or similar models. 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. Holley Ultra Lo-Ram intake manifold kits include all the sealing o-rings, plugs, and fasteners required for the installation of the kit.


  • Designed for GM LS Gen III and IV engines equipped with GM LS1/2/6 (cathedral port) cylinder heads
  • Provides best performance for forced induction (supercharged or turbocharged) engine applications with peak power at 7000-8000 rpm, depending on the application
  • Dual-injector, separate-passage, high-volume fuel rails with mounting hardware, dual-fuel capable, 8 AN o-ring ports
  • Modular LS1 Lo-Ram design allows customization for user desired configurations
  • Low height & compact packaging allows installation in most applications often under stock hoods
  • Available with both as-cast satin and black power-coat finishes

About Holley EFI

Holley is the new standard in EFI! Whether you're engine swapping your classic street car or need to manage 4000 horsepower in your twin-turbocharged drag radial race car, Holley EFI has the solutions you need to get your project up and running better than ever!

BrandHolley EFI
Emission Code3
EngineGM LS1/LS2/LS6
Fuel System TypeEFI
Injector QuantityDual
Inlet LocationFront
Manifold TypeUltra Lo-Ram
Product TypeIntake Manifold Base
WarrantyLimited 90 Day
Part Number300-603

This part is legal for sale and use on Uncontrolled (Non-Emissions Controlled) Vehicles and Racing Use Only Vehicles.

The following vehicles are considered Uncontrolled (Non-Emissions Controlled) Vehicles:

  • 1965 and older U.S. manufactured California Certified vehicles
  • 1967 and older U.S. manufactured Federally Certified vehicles
  • 1967 and older Foreign manufactured vehicle

The following vehicles are considered Racing Use Only Vehicles:

  • Racing Use Only Vehicles are vehicles that are used exclusively for competition and that are not registered and that may never be used on the street

WARNING: It is against the law to install this part on an Emissions Controlled Vehicle

The following vehicles are considered Emissions Controlled Vehicles:

  • 1966 and newer U.S. manufactured California Certified vehicles
  • 1968 and newer U.S. manufactured Federally Certified vehicles
  • 1968 and newer Foreign manufactured vehicle
Limited 90 Day: See Details

*Free Shipping & Handling only offered to the contiguous US on orders over $100, excludes clearance parts and oversized packages.

Some parts are not legal for use in California or other states with similar regulations.