PRODUCT DETAILS
Radium Engineering Fuel Rail - 2000-2009 Honda S2000
You're building your S2000 and you need a fuel rail that can actually flow enough fuel for your setup without becoming a restriction. The stock fuel rail's got a small internal bore and it chokes fuel flow once you start pushing serious power or running E85. Radium Engineering makes this billet aluminum fuel rail with a 0.69 inch internal bore. That's way bigger than stock. You're flowing enough fuel for high-flow injectors, E85, or turbo builds without the fuel rail becoming the bottleneck. Radium makes two versions of this rail: one for 2000-2005 S2000s and one for 2006-2009 S2000s (including the 2008-2009 CR). The 2000-2005 version mounts to all five factory mounting bosses on the AP1 chassis. The 2006-2009 version's designed for the AP2 chassis and uses a different mounting style. The images show the 2000-2005 version. Both rails are machined from billet aluminum, anodized, and laser-etched. The fuel rail ports are tapped for 8AN ORB fittings. The small port where the factory fuel pressure regulator goes is tapped for 1/8 NPT so you can run a fuel pressure gauge or plug it if you're running an aftermarket regulator somewhere else. These rails do NOT come with fittings or fuel line. You need to buy those separately based on your setup. You'll need 8AN ORB fittings for the main fuel rail ports and 1/8 NPT fittings if you're using the small port. This is an upgrade rail, not a top-feed conversion. You're reusing your stock fuel injectors or running OEM-equivalent injectors with the same height and O-ring sizes.
2000-2005 AP1 Version vs. 2006-2009 AP2 Version
Radium makes two different fuel rails for the S2000 and they're not interchangeable. The 2000-2005 AP1 version (part number 20-0591-02) is designed for the earlier chassis. It uses all five factory mounting bosses and it's a direct bolt-in for AP1 cars. The 2006-2009 AP2 version is designed for the later chassis including the 2008-2009 CR models. The AP2 chassis has a different mounting configuration so the fuel rail's designed differently to accommodate that. Both rails have the same 0.69 inch internal bore and the same 8AN ORB ports. Both rails are machined, anodized, and laser-etched. The difference is in how they mount to the engine. Make sure you're ordering the correct version for your chassis. The images on this page show the 2000-2005 AP1 version. If you're ordering the 2006-2009 AP2 version, the mounting style will be different but the overall design and port locations are similar.
Here's Why the Stock Fuel Rail Becomes a Restriction
The stock S2000 fuel rail's got a small internal bore. It works fine for a stock engine making stock power on pump gas. It's not fine when you're running E85 and you need 30-40% more fuel volume than pump gas requires. It's not fine when you're running a turbo and you need high-flow injectors. The small bore creates a pressure drop from one end of the rail to the other. The injector closest to the fuel inlet gets full fuel pressure. The injector farthest from the inlet gets less pressure because the fuel's losing pressure as it flows through the small bore. That causes uneven fueling between cylinders. You're tuning for the leanest cylinder and you're over-fueling the other three cylinders to compensate. Radium's fuel rail fixes that with a 0.69 inch bore. The larger bore means less restriction and more even fuel pressure distribution across all four injectors. You get consistent fueling, better tuning resolution, and you're not leaving power on the table because of a restrictive fuel rail.
Works with Stock Injectors or OEM-Equivalent Injectors
This is an upgrade rail, not a top-feed conversion rail. That means you're reusing your stock fuel injectors or you're running aftermarket injectors that are the same physical size as stock. The injectors need to be the same height as stock and the upper and lower O-rings need to match the stock diameters and styles. If you want to run injectors that are a different size or a different style (like side-feed to top-feed conversion), this rail won't work. You'd need a different rail. Radium doesn't make fuel injector recommendations. You need to talk to your tuner about what injector flow rate you need for your setup. Then you need to talk to the injector manufacturer to make sure the injectors you're buying have the correct physical dimensions to fit this rail with stock-size O-rings. Most people running this rail are either keeping stock injectors or upgrading to higher-flow injectors from Injector Dynamics, Bosch, or Deatschwerks that are designed as OEM replacements for the S2000.
8AN ORB Ports and 1/8 NPT Port
The fuel rail's got two large ports tapped for 8AN ORB fittings. ORB stands for O-ring boss. That's a straight-thread port with an O-ring groove. You're threading 8AN ORB fittings into the ports and the O-ring seals against the groove. 8AN ORB fittings are available in different styles: adapters to 8AN hose ends, direct-mount fuel pressure regulators, or fuel pulse dampers. You pick the fittings based on your fuel system setup. If you're running an aftermarket fuel pressure regulator mounted on the rail, you use an 8AN ORB direct-mount regulator. If you're running a regulator somewhere else in the engine bay, you use 8AN ORB to 8AN adapters and run braided fuel line from the rail to the regulator. The small port where the factory fuel pressure regulator mounts is tapped for 1/8 NPT. If you're running the stock fuel pressure regulator, you don't use this port. If you're running an aftermarket regulator, you can thread a 1/8 NPT fuel pressure gauge into this port to monitor rail pressure or you can plug it with a 1/8 NPT plug.
No Fittings or Fuel Line Included - You Need to Buy Those Separately
These fuel rails do NOT come with fittings or fuel line. Radium sells them as bare rails because everyone's fuel system setup is different. If you're running a return-style fuel system with a regulator on the rail, you need different fittings than someone running a returnless system with a regulator at the tank. Here's what you need to buy separately to complete the install. You need two 8AN ORB fittings for the main fuel rail ports. Those can be 8AN ORB to 8AN male adapters if you're running braided fuel line, or they can be direct-mount accessories like a fuel pressure regulator or a fuel pulse damper. You'll also need 8AN braided stainless fuel line and 8AN hose ends to connect the rail to your fuel system. If you're using the 1/8 NPT port, you need either a 1/8 NPT fuel pressure gauge or a 1/8 NPT plug. Make sure you've got room around the fuel rail ports for whatever fittings or accessories you're installing. A direct-mount fuel pressure regulator or a fuel pulse damper takes up space and you need to make sure it clears your intake manifold and your throttle body.
Installation Notes - Vacuum Hose Included
The 2000-2005 AP1 version mounts to all five factory mounting bosses so it's a direct bolt-in. You're pulling the stock fuel rail off, installing this rail with your stock injectors or new injectors, and bolting it down. Radium includes replacement vacuum tubing with the AP1 version to simplify the install and eliminate the factory hard lines that run from the air pump system. You're replacing those hard metal tubes with flexible vacuum hose. That cleans up the engine bay and makes the install easier. You'll also need to remove the factory fuel rail cover on both AP1 and AP2 cars. The Radium rail's taller than the stock rail so the cover won't fit. Most people building an S2000 don't care about the cover because they want to see the billet fuel rail anyway. The 2006-2009 AP2 version installs differently because of the different mounting configuration on the later chassis, but the basic process is the same: remove stock rail, install Radium rail, bolt it down.
What You Get
- Radium Engineering billet aluminum fuel rail (select 2000-2005 AP1 or 2006-2009 AP2 version)
- 0.69 inch internal bore (larger than stock for improved fuel flow)
- Machined, anodized, and laser-etched finish
- Two 8AN ORB fuel rail ports (fittings NOT included)
- One 1/8 NPT port for fuel pressure gauge or plug (fitting NOT included)
- 2000-2005 AP1 version: mounts to all five factory mounting bosses, includes replacement vacuum tubing
- 2006-2009 AP2 version: designed for AP2 chassis mounting configuration (including 2008-2009 CR)
- Compatible with stock fuel injectors or OEM-equivalent injectors
- E85 and alcohol fuel compatible
- Made in USA
Fits Your Car
- 2000-2005 Honda S2000 (AP1 chassis) - use part number 20-0591-02
- 2006-2009 Honda S2000 (AP2 chassis, all models including 2008-2009 CR) - use AP2-specific version
Note: There are TWO versions of this fuel rail - one for 2000-2005 AP1 chassis and one for 2006-2009 AP2 chassis. They are NOT interchangeable. The AP1 version uses all five factory mounting bosses. The AP2 version uses a different mounting configuration for the later chassis. Make sure you select the correct version for your year. The images shown are of the 2000-2005 AP1 version - the 2006-2009 AP2 version will have different mounting but similar overall design and port locations. These fuel rails do NOT include fittings or fuel line - you MUST purchase these separately. You need two 8AN ORB fittings for the main fuel rail ports (either 8AN ORB to 8AN adapters, direct-mount regulators, or fuel pulse dampers). You also need 8AN braided stainless fuel line and 8AN hose ends to connect the rail to your fuel system. If you're using the 1/8 NPT port, you need a 1/8 NPT fuel pressure gauge or a 1/8 NPT plug. This is an upgrade rail - you MUST use stock fuel injectors or OEM-equivalent injectors with the same height and O-ring sizes as stock. This is NOT a top-feed conversion rail. Consult your tuner for injector flow rate recommendations and consult the injector manufacturer to confirm physical dimensions before ordering injectors. Requires removal of factory fuel rail cover on both AP1 and AP2 cars (cover will not fit over Radium rail). The 2000-2005 AP1 version includes replacement vacuum tubing to eliminate factory air pump hard lines during installation. Make sure you have adequate clearance around the fuel rail ports for whatever fittings or accessories you're installing - direct-mount regulators and fuel pulse dampers are large and may interfere with intake manifold or throttle body depending on your setup. Works with all fuel types including E85 and alcohol blends.