RCM Cylinder 4 Cooling Mod Kit

Cylinder four runs hotter than the other three on Subaru's EJ engines. It is a design consequence, not a fault: the way the water passageways are routed at the back of the block means coolant flow around that cylinder is the weakest in the engine, and the temperature difference shows up exactly where you least want it on a tuned motor.

The RCM Cylinder 4 Cooling Mod Kit is the fix, and it is a bolt-on. There is an unused port at the back of the block at cylinder four's location. The kit feeds that port and tees it into the water matrix pipe directly above, adding flow where the factory design left it short.

What is in this kit

• Custom 90-degree Samco silicone hose — pre-formed, so the flow is not disturbed by a kink in the pipework.
• Billet fittings, banded in place on the hose.
• HiGrip stainless steel fittings for the tee into the water matrix pipe.

The billet barb is sized deliberately. Its internal diameter sets the flow rate around cylinder four high enough to cool it and no higher — the point is to even the engine out, not to overcool one cylinder.

Full kit or Street Spec?

This is the full kit: pre-formed Samco silicone hose and stainless HiGrip fittings. The Street Spec kit does the same job for less, using quality coolant hose with genuine Subaru clamps and two supplied pipe lengths you cut to suit. Same barb sizing, same principle; the difference is hose quality, fittings and how much fitting work you do yourself.

Fitting

No machining and no modification to the block — the port it uses is already there and unused from the factory. We fit these as part of engine builds at our Red Deer shop, and our own GC8 drag car runs one alongside the rest of its RCM hardware.

Not sure whether your engine has the port, or which kit suits your build? Send us the engine and we will confirm before you order. More RCM parts in our Roger Clark Motorsport range.