Catch Can & Breather Line Sizing
Size your catch can correctly for your engine — from a mild street build to a full track car. Recommendations account for engine displacement, cylinder count, forced induction, track use, and how frequently you plan to drain the can.
Engine Configuration
Sizing Recommendation
Minimum Volume
100
ml (bare minimum)
Recommended Volume
100
ml (street / track)
Competition Volume
150
ml (race build)
Breather Line Size
-6
-6 (AN6)
Rocker Cover Port Size
M12×1.5 or 1/4" NPT
Recommended Thread
M12×1.5
Vent Ports Needed
1 inlet port
Common Port Thread Reference
| Thread | Bore approx. | AN Compatible |
|---|---|---|
| M12×1.5 | 10.5 mm | -6 (AN6) |
| M14×1.5 | 12.5 mm | -8 (AN8) |
| 1/8" NPT | 8.5 mm | -4 (AN4) |
| 1/4" NPT | 10.9 mm | -6 (AN6) |
| 3/8" NPT | 15 mm | -8 (AN8) |
| OEM hose barb (various) | 16 mm | -8 or -10 (adaptor needed) |
Why a Catch Can?
Protect your intake tract. Blow-by gases from the crankcase contain oil mist that coats intake ports, valves and intercooler cores, reducing efficiency and causing carbon build-up on direct-injection engines that cannot self-clean their intake valves.
Baffled cans are far superior. A simple empty canister barely captures any oil before it passes through to the intake. A baffled or coalescing media catch can separates oil from gas efficiently with significantly less volume.
Open vs closed system. A closed system recirculates cleaned blow-by gas back into the intake. An open system vents to atmosphere (often required for time attack / circuit racing). Legislation may require a closed system on road-registered vehicles.
Drain before it overflows. A full catch can will push oil-laden air back into the intake, negating the entire purpose. Drain regularly — especially before circuit events and endurance races.