In this second instalment of auto basics I will discuss blow-by.

In the heart of your engine there is a cylinder which houses an explosion. There are a few actually. As a base for the cylinder there is a piston that moves up and down. This piston helps us suck in fuel and air which it then compresses so that the spark plug can ignite it. The ignition causes the air and fuel mixture to explode and the pressure created pushes the piston back down. It is this explosion that creates motion which is delivered through various other parts all the way to your wheels. In order to maximise the explosive force the cylinder needs to be properly sealed. Without the proper seal some of this pressure will escape taking along with it some of our power. Helping us seal this chamber are a set of rings around the piston head. The rings, apart from their primary use of providing a seal to contain the explosion, are also used for oil management in the cylinder.

Blow-by is the process where leaks occur from the combustion chamber to your crankcase. It happens in all engines in varying degrees. The older the engine the more blow-by you are likely to have. It is the fuel, air, moisture and exhaust gasses that escape past the piston rings and into the bowels of your engine. Much like a human body, the engine needs to fart out these gasses or it will turn to shit. Ummm. Right. If we were to leave these by-products in the bowels of our engine it will dilute our oil which decreases its ability to lubricate. The crankcase will also have to deal with constant pressure changes as the pistons go up and down. To combat this engines draw air in through the air filter system, feed it into the engine at the valve cover while sucking it out elsewhere to expel the gasses. The gas has to go somewhere and the environmentally sound thing to do is send it back into the intake system to be burned safely once they reach the combustion chamber.

The problem with the above system is that it was created with emissions in mind and not in the best interests of your engine. Oil vapours are unintentionally sucked into your intake system which is not good for your engine. They can cause pinging and over time they will gum up your intake valves, solenoids and sensors. To prevent this you can run an oil catch can which will do what its name suggests. Running a catch can with a filter you can completely bypass feeding your intake system with crap. This will be vented into the atmosphere which isn’t exactly environmentally friendly but in case you haven’t noticed you are driving a car. There are recirculating systems which catch the oil and still circulate the air back into your intake system allowing your environmentally peace loving self to feel good as you rev to 7,000 rpm in first gear.

Where an engine is used as a daily driver around town and the oil is changed at regular intervals a catch can is not required. But if you drive your car hard, such as at the track, lateral forces and other ungodly insane pressures will result in oil being fed to your intake system. It’s not something you want your intake to handle so a catch can, recirculating or atmo venting, is a must. There are many option available some of which include a coke can and some garden hose. I suggest any system that allows you to see the amount of oil accumulated to avoid overflow. Whichever way you go, do install a catch can before you drive your car the way it was meant to be driven.

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