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An oil catch can is essential on a performance vehicle to protect the engine from elevated levels of crankcase blow-by accumulated from high performance driving. Excess oil saturated air circulating back into the air intake stream can lead to degraded performance. Radium Engineering catch cans feature large 10AN ORB ports, a 4AN ORB drain port, 2-step oil separation baffling, and an O-ring sealed dipstick.
Benefits:
-Effectively raises the octane and increased engine performance from cleaner inlet air
-Prevents oil buildup in the intake and intercooler system walls, throttle body, intake manifold, etc.
-Excessive oil collection can be an indicator of a damaged engine.
-Lowers hydrocarbon emissions
-Capacity: 8 fluid ounces each
Details:
These Radium catch can kits are compatible with 1990-2005 Mazda MX-5 Miata with both the 1.6L and 1.8L engines. They mount using OEM holes and integrate perfectly with the surrounding components. NOTE: the factory air intake box cannot be used with these kits. Reference the installation pictures before ordering. 
The kits are not designed for vent-to-atmosphere (VTA), thus are emissions and track legal. This closed loop system removes oil and sludge from the PCV gasses before it is routed to the engine to be burned. A closed loop system also promotes negative crankcase pressure for optimal performance. Furthermore, closed systems prevent unwanted oil vapors from entering the cabin. The dipsticks built into the catch cans allow easy inspection of accumulated fluid. No cutting, drilling or permanent modification to the vehicle is required.
If purchasing the single catch can kit, there is enough components to plumb it to the PCV or the crankcase side of the engine (see below for more info). If purchasing the dual catch can kit, all engine breather ports will be isolated for optimal performance. 
When using the catch can on the PCV side, it runs inline with the PCV (positive crankcase ventilation) valve and retains it's factory function. When the intake manifold pressure is close to or greater than atmospheric pressure, the PCV "check" valve closes and, thus, this hose experiences no flow. Conversely, the PCV hose will experience "metered" vacuum when the engine is idling, steady state cruising, and decelerating. This would normally draw unwanted crankcase vapor, unspent fuel, and oil sludge into the intake manifold immediately after a high load run. Note: Because the Radium catch cans are pressure sealed, they are great for this boosted application so intake manifold connection is permitted.
When using the catch can on the crankcase side, it runs inline with the crankcase breather port. At low loads it experiences atmospheric pressure, but when the engine is at high load (WOT), this hose will experience high flow out of the crankcase. This would normally lead to oil and sludge accumulation in the air filter intake pipe. Oil accumulation will occur in the intercooler which lowers the thermal efficiency properties of the heat exchanger and leads to decreased performance.
The 20-0336 Catch Can Kit, 90-05 Mazda MX-5 is shown below.
The 20-0337 Dual Catch Can Kit, 90-05 Mazda MX-5 is shown below. 