Hybrid Racing - PRB RWD Coolant Port Adapter for K20A/K20Z1/K24A1

Hybrid Racing RWD PRB Coolant Housing Adapter - K20A, K20A2, K20A3, K20Z1 & K24A1

Put a K-series in a rear-wheel-drive chassis and you find out fast how little room there is between the back of the head and the firewall. The factory coolant outlet points right into that space, which is the last direction you want it going. This adapter turns the radiator outlet out the side of the cylinder head instead, so you get your firewall clearance back and a much more sensible path for your hoses. It's compact, machined from a single piece of 6061, and built specifically for RWD conversions rather than adapted into one.

Read This First: You Need An RWD Intake Manifold

Most important thing on this page, so don't skip past it. Because the radiator outlet exits from the side of the cylinder head, this adapter is not compatible with standard front-wheel-drive K-series intake manifolds. The outlet will physically interfere with the throttle body. There's no working around it with different hoses or clocking.

This has to be used with a rear-wheel-drive-specific intake manifold that provides clearance for the side-exit outlet. So confirm what manifold you're running, or what you're planning to buy, before you order this. If you're still on a factory FWD manifold, our standard PRB coolant housing adapter is the one that fits your setup.

Built For Tight RWD Engine Bays

The side-exit design exists for one reason: firewall clearance. In an S2000, a 240SX, a BRZ, a BMW 3 Series, a Miata, or any of the other chassis people are dropping K-series into, the space behind the head is the tightest real estate in the whole bay. Point the coolant outlet back there and you're routing hoses through a gap that barely exists, usually with a bend that pinches flow. Turning it out the side gets that hose into open space and gives you a straighter shot at the radiator. It's a small change in geometry that makes a real difference in how buildable the car is.

Put Your Coolant Temp Sensor Where It Belongs

There's a 1/8-inch NPT port machined into the top of the housing, and on an RWD swap it's genuinely handy. Most of these builds are running a standalone ECU and aftermarket gauges, which means you need a proper home for a coolant temperature sensor. This gives you one built into the part, so you're not splicing an inline adapter into a radiator hose or hunting for a bung somewhere. It threads in clean and reads real coolant temperature right at the head.

It Seals With Rubber, Not RTV

This matters even more on a swap, because the last place you want a coolant leak is somewhere you can barely reach. A precision-machined pocket accepts an OEM-style rubber seal, so you get a proper mechanical seal against the head instead of relying on a bead of RTV and hoping. It goes on once, it seals, and you can move on to the next thing on your list.

Keeps The Thermostat Bypass Circuit

Easy to overlook, but worth having. This adapter retains the factory thermostat bypass circuit, so coolant circulates properly during warm-up and the engine comes up to temperature the way it should. You get the custom packaging flexibility a swap needs without throwing away the part of the factory system that's actually doing useful work.

Run Factory Hoses Or Go Full AN

The outlet is a threaded -16 ORB. Use the included hose barb fitting for a conventional factory-style radiator hose, or thread in a -16 ORB AN fitting if you're plumbing the whole cooling system in AN line, which plenty of RWD swap builds end up doing anyway. Your call, and you're not buying a second housing when the build evolves.

What's In The Kit

• Billet coolant port adapter
• OEM-style sealing gasket
• Mounting hardware
• -16 ORB to hose barb radiator fitting

Fits These PRB-Head K-Series Engines

Because it bolts to the head rather than the chassis, it works in any rear-wheel-drive conversion using one of these engines, including the Honda S2000, Nissan 240SX, Subaru BRZ, BMW 3 Series, Mazda Miata, and plenty of others, as long as you're running an RWD-specific intake manifold.

Who Should Run This Coolant Housing

This is for the builder doing a rear-wheel-drive K-swap who's already measured the gap behind the head and knows how tight it is. You've got an RWD manifold, you're plumbing a custom cooling system, and you need the coolant going out the side instead of into the firewall. This gives you that in a compact, well-made housing that seals properly, keeps the bypass circuit, and gives your temp sensor a home. Check your manifold, bolt it on, and get your cooling packaged the way it needs to be.

Fits: PRB-style K-series cylinder heads, K20A, K20A2, K20A3, K20Z1, and K24A1, in rear-wheel-drive conversions (S2000, 240SX, BRZ, BMW 3 Series, Miata, and similar). Requires: a rear-wheel-drive-specific intake manifold. Not compatible with: standard front-wheel-drive K-series intake manifolds, the outlet interferes with the throttle body. Material: single-piece 6061 aluminum, black anodized. Outlet: -16 ORB, side-exit, works with the included hose barb fitting or a -16 ORB AN fitting. Sensor port: 1/8" NPT on top for a coolant temp sensor. Sealing: machined pocket with OEM-style rubber seal, no RTV required. Retains:factory thermostat bypass circuit. Includes: adapter, OEM-style gasket, mounting hardware, and -16 ORB to hose barb radiator fitting.