Anyone who's put a K-series into a rear-wheel-drive chassis knows the problem: the firewall is right there. The standard coolant housing exits out the side of the head, and in a tight RWD bay that's exactly the wrong direction. This adapter fixes it by routing the coolant outlet straight off the back of the cylinder head instead, which is a much smarter path when you're fighting for every millimeter behind the motor. It's compact, it's machined from a single piece of 6061, and it turns a packaging headache into a clean, sensible cooling layout.

Manifold Compatibility

This is the most important thing on the page, so don't skip it. Because the coolant outlet exits from the rear of the cylinder head, this adapter is not compatible with standard transverse K-series intake manifolds, and that includes the factory PRB, RBC, and RRC manifolds. There simply isn't clearance behind the head with those manifolds in place.

This is built for use with rear-wheel-drive-specific intake manifolds that leave room behind the cylinder head. So confirm what manifold you're running, or planning to run, before you order. If you're still on a factory transverse manifold, this isn't your adapter yet, and if your RWD build is running the standard side-exit setup, our FWD RBC coolant housing adapter is the one you want.

Built For Tight RWD Engine Bays

The rear-exit design is the whole reason this part exists. In an S2000, a BRZ, a BMW, or any other RWD chassis taking a K-series, the space between the back of the head and the firewall is at a premium, and a side-exit housing eats into it while forcing your hoses on an awkward detour. Pulling the outlet straight off the back gives you a shorter, more direct path to the radiator and frees up room you genuinely need for everything else back there. It's a smaller footprint doing a better job, which is exactly what a tight swap calls for.

Keep Your Heater Or Do A Clean Heater Delete

You get both options in the box, so you decide with the parts in hand rather than at checkout.

Keeping the heater? Use the supplied threaded fitting and your heater core stays connected. If the car sees street duty or cold weather, go this route.

Doing a heater delete? Cap it with the included -8 ORB plug and move on. Fewer hoses, less clutter, one less thing to leak in a bay where space is already tight. That's usually the call on a dedicated track or race build.

Run Factory Hoses Or Go Full AN

The outlet is a threaded -16 ORB. Thread in the included -16 ORB to hose barb fitting and you're running conventional radiator hoses. Or run a -16AN fitting (sold separately) if you're plumbing the whole cooling system in AN line, which a lot of RWD swap builds end up doing anyway. Either way you're not locked in, and you're not buying a second housing when the build evolves.It is recommended to change out the factory constant tension spring clamps with Hybrid Racing T-Bolt Clamps to ensure a proper seal. Old constant tension clamps can lose their ability to seal the factory hose to the new coolant port fittings.

Machined For Flow, Not Just For Packaging

The internal coolant passage is fully machined rather than left as-cast, so coolant moves through smoothly without unnecessary turbulence or restriction. That's the part that separates a well-made adapter from one that just looks the part. You get the compact rear-exit packaging and you keep proper flow, along with OEM-quality sealing, which matters a lot on a swap where you don't want to be chasing a coolant leak behind the engine.

What's In The Kit

• Billet coolant port adapter
• Stamped steel gasket
• Mounting hardware
• -8 ORB plug (for heater delete)
• Threaded heater hose fitting (to retain the heater)
• -16 ORB to hose barb radiator fitting

Who Should Run This Coolant Housing

This is for the builder doing a rear-wheel-drive K-swap who's already discovered how little room there is behind the head. You've got an RWD-specific manifold, you're plumbing a custom cooling system, and you need the coolant to exit the back of the motor instead of the side. This gives you that in a compact, well-made package that flows properly and seals like it should. Confirm your manifold, pick your heater config, and get your cooling sorted.

Fits: RBC-head K-series engines, K20Z3, K24A2, K24A4, K24A8, and K24Z7, in rear-wheel-drive conversions (S2000, BRZ, BMW, and similar). Requires: an RWD-specific intake manifold. Not compatible with: standard transverse K-series manifolds including factory PRB, RBC, and RRC. Material: single-piece 6061 aluminum, black anodized. Outlet: -16 ORB, rear-exit, works with the included hose barb fitting or a -16AN fitting (sold separately). Heater port: retain with the supplied threaded fitting or seal with the included -8 ORB plug. Coolant passage: fully machined for unrestricted flow. Includes: adapter, stamped steel gasket, mounting hardware, -8 ORB plug, threaded heater fitting, and -16 ORB to hose barb radiator fitting.