As more and more vehicles on the road today are switching to turbo, the use of catch cans have become a hot topic across the industry. How do they work? Are they necessary in today's ultra modern powertrain designs?
Before we explain why they're necessary, let's talk about how they work. When the pistons go up and down as part of the normal four-stroke cycle a lot of gas pressure is created. Ideally, that gas cannot escape past the piston seals down into the crankcase, but nothing is perfect so inevitably some gas manages to get past – this is called ‘blow by’, as it “blows by” the piston seals into the crankcase. This gas needs to be expelled as its not helping with lubrication, and with lots of gas in the crankcase you get a positive crankcase pressure, which means it's harder for the piston to move up and down. Blow-by tends to get worse with an engine’s age.
Enter the PCV, or positive crankcase ventilation system. This works pretty simply; air is piped to the crankcase via the engine’s existing air filter, run through the crankcase, and then through a PCV valve back into the engine’s air intake. The problem with the PCV system is that some of that nasty, oily air can find its way back into the engine’s cylinders, which work best with clean fresh air that can be mixed with the right amount of fresh fuel. Using the ex-crankcase air is inefficient, and tends to build up sludge over time.
Enter the catch can system. A typical catch can setup consists of either two cans, or a single can with two inputs and outputs. The function of an Oil Catch Can is simple, it connects in line with the PCV and Crankcase ventilation systems, and passes the oil-saturated air through a series of baffles in order to separate the oil vapor from the air. The air is allowed to pass through the system and back in to the intake and throttle body, and the oil is trapped in the can where it can be drained, therefore reducing or completely eliminating the problems associated with blow-by.