Hybrid Racing PRB FWD Coolant Port Adapter - 02-06 RSX / 02-05 Civic Si

The factory coolant outlet on a PRB head is a cluttered piece of hardware, and it drags the idle air assist valve along with it. This adapter replaces the whole arrangement with one compact billet housing that cleans up the back of your motor, deletes the idle air assist valve, and gives you a proper -16 ORB outlet to plumb however you want. It's machined from a single piece of 6061 and finished in black anodize, and it's the kind of part that makes a bay look sorted instead of stock.

Deletes The Idle Air Assist Valve

This is one of the main reasons people grab this adapter. The idle air assist valve mounts to the factory coolant port, and on a built or swapped engine it's usually just clutter you don't need anymore. Installing this housing removes it from the equation entirely, which means fewer hoses, fewer fittings, and one less thing hanging off the back of the head. If you're tidying up a bay or simplifying a swap, that alone is worth the swap.

Put Your Coolant Temp Sensor Where It Belongs

There's a 1/8-inch NPT port machined into the top of the housing, which gives you a clean, purpose-built spot for a coolant temperature sensor. No inline radiator hose adapter, no separate sensor bung spliced into a hose, no compromise. Running a standalone ECU, a gauge, or an aftermarket sensor? It threads right in where it should be. Not using it? Cap it with the included plug and it disappears. Either way you've got the option built into the part rather than hunting for a place to put a sensor later.

It Seals With Rubber, Not RTV

This matters more than it sounds. Plenty of adapters in this space rely on a bead of RTV to seal against the head, which works right up until it doesn't, and then you're pulling the part back off to redo it. Ours has a precision-machined pocket that accepts an OEM-style rubber seal, so you get a proper mechanical seal the way Honda designed it. It goes on once, it seals, and you're not chasing a weep six months later.

Keeps The Thermostat Bypass Circuit

Worth calling out because it's easy to overlook. This adapter retains the factory thermostat bypass circuit, so your coolant still flows correctly during warm-up and the engine comes up to temperature the way it's supposed to. You're getting the custom plumbing flexibility without giving up the part of the factory system that actually does something useful.

Run Factory Hoses Or Go Full AN

The outlet is a threaded -16 ORB. Use the included hose barb fitting and you're on a standard factory-style radiator hose with no fuss. Or thread in a -16 ORB AN fitting if you're plumbing the cooling system in AN line. There's also a threaded heater hose fitting included, so you can keep your heater circuit connected if the car sees street duty. You're not locked into one setup and you're not buying a second housing when the build changes.

Machined For Flow

The internal coolant passage is carefully machined rather than left rough, so coolant moves through smoothly instead of hitting restrictions on its way out of the head. You get the compact billet appearance and the plumbing flexibility while the cooling system performs like it should. That's the whole balance a part like this has to strike.

What's In The Kit

• Billet coolant port adapter
• OEM-style sealing gasket
• Mounting hardware
• -16 ORB to hose barb radiator fitting
• Threaded heater hose fitting
• Plug for the 1/8" NPT sensor port