Oil catch-cans are aftermarket modifications that almost any race car will utilize to full effect. If you want to race, this will help you keep your oil and gas separate and clean. Here's how they work.
As your average engine goes through its four cycles of Intake-Compression-Combustion(Power)-Exhaust, on the downward piston stroke of the combustion cycle, the explosive pressures caused by the combustion forces some of the gas and pressure to get past the piston rings, a phenomenon also known as blow-by because of the gasses literally blowing by the piston rings.
As these gasses blow by the piston rings, it atomizes the oil in your engine's crankcase, causing pressure inside the crankcase which can damage or even destroy your engine, and its ability to produce power. So, to prevent this modern engines have something called a PCV (Positive Crankcase Ventilation) Valve, and what this valve does is allows those gasses and pressure to escape from the crankcase, Originally these gasses were allowed to vent into the atmosphere, but in the last 40-50 years, due to environmental risks and dangers, the EPA and other world environmental agencies has banned this, so modern engines have an enclosed PCV system. This means that cars no longer smell as dirty and oily as before, as well as not smelling as much like gasoline because of other systems. When a classic car drives past, you have probably noticed that it smells different. This is why.
Therefore, to enable the enclosed PCV valve to work, these gasses had to go somewhere. The engineers asked themselves, "why not re-burn it?" This design solved a large portion of the environmental concerns, by ensuring that the unburnt fuel fumes in the blow-by gasses were no longer vented to atmosphere, but instead were burned. However, you couldn't always separate fuel and engine oil, and the oil could be damaging to the environment if burned, and oil doesn't have the same power-producing properties as gasoline.
So in order to re-burn these blow-by gasses the gasses are routed through the PCV valve back through the intake manifold behind the throttle body.
Most PCV valves are located on the Valve cover and are visible just by popping the hood. If you're not sure check with manufacturer.
As the blow-by gasses pass through the PCV valve and back into the intake manifold, there is atomized engine oil in the blow-by gasses which comes in contact with everything along the path. PCV valve, hosing, intake manifold, and eventually your intake valves. As time passes this oil contacting the entire system will create a sludge looking substance (if you have ever cleaned your throttle body you will know what I`m talking about.) As the sludge builds up on your intake manifold and intake valves, and is then burned during the combustion cycle, creating carbon build up. Also, any restricted airflow due to a build up of sludge or carbon in your intake manifold and intake valves can rob power, efficiency and reliability out of your engine., the same as with any air and fuel displaced by the oil in the gasses, by impurifying the gasoline meant to burn and push the piston downward on the combustion cycle.
So what an oil catch can does is, as these gasses go through your PCV valve, you do not want the oil in the gasses entering your engine. Well, that`s where the catch can comes in. A catch can is a filter to catch the oil as it passes through the catch can while allowing the pressure and now filtered blow-by gasses to be safely re-burned in the engines combustion chamber. By not allowing oil to accumulate on the intake manifold and valves, this increases engine life and maintain power and efficiency, which can eliminate costly engine repairs in the future allowing you to enjoy your vehicle for many years to come.
Which types of engines get the most benefit from a catch can?
All engine types can, and will benefit from the use of a catch can, but there are a few types of engine that get even more benefit from having a catch can installed, for example:
GDI (Gasoline Direct Injection)
As the name suggests, GDI uses a system to directly inject fuel in the combustion Chamber which results in the use of a Dry manifold which means fuel is not injected before the valves.
This is the opposite for an engine with MPI (multi port Injection) where fuel is injected before the valves, also known as a Wet Manifold injection, where the fuel is used to break down a lot of the carbon build up on the valves.
But since a dry injection system doesn't have that ability, Carbon is allowed to build up on the intake valves which can rob power, efficiency and reliability from the engine.
High Performance Engines
Any vehicle with a engine that is turbocharged, supercharged, or a high compression ratio, will also get more benefit from a catch can, due to the fact that with these engine types the amount of blow-by gasses will be greater, due to the increased forces involved with the combustion cycles on a high performance engine.
How Can a Catch Can Benefit You?
Well, the many ways a catch can will benefit you is saving you money on costly repairs in the long run, the added peace of mind knowing that your investment is protected, the maintained efficiency of your engine due to the reduction of efficiency robbing carbon build up, and it's a good way to visually see your oil consumption rate because all engines consume oil because of the way internal combustion engines work, and if you're a automotive enthusiast like myself, knowing that your engine is running at the best that it can is exciting and reassuring.
What's the drawback?
Cost, primarily. With most catch-cans costing $80-400, it can be fairly expensive. The only real reason why the manufacturers don't want to install catch cans from the factory, is primarily the cost, but also the fact that you will occasionally have to drain the oil from your catch can, when it gets near-to-full. Unfortunately, many people overlook routine maintenance, and if a catch can were to ever overflow, it could cause issues. But, anyone who knows how to install a catch can will also know how to remove it, and so emptying the catch can is simple!