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Turbo Systems: PCV options and information
What is PCV?
A certain amount of gas, known as 'blowby gas', escapes around the pistons while the engine is running. PCV, Positive Crankcase Ventilation, is a system that allows venting of this hydrocarbon-rich gas out of the crankcase.
A N/A PCV setup is usually looks like this:
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The breather is simply a straight-through fitting, while the PCV valve is a special valve which is closed when there is too much pressure difference on its ends, in this case when there is too much vacuum in the IM (e.g. at idle). There are different ways in which this system vents gases:
1) At idle, the PCV valve is fairly closed, so the majority of the little blowby gas escapes through the breather.
2) At part-throttle, the PCV valve is open and the vacuum from the IM sucks gas out of the crankcase; fresh air is brought in through the breather
3) At wide-open throttle, gases escape through both the breather and the PCV valve
Unfortunately, this setup cannot be used if you are turbocharging your vehicle; the boost will leak though the breather (and even PCV depending on the valve) and pressurize the entire crankcase; the blowby won't have anywhere to escape..
Option 1 - Recommended for low boost levels
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Keep the idea of the stock system, but breather goes to atmosphere instead of intake; an oil catch can is added to catch any oil coming out of the breather; the can also has a filter to keep junk out of the crankcase. An oil catch can is added between the IM and PCV valve, and - most importantly - a check valve which closes off whenever there is boost in the IM, avoiding any boost leak into the crankcase.
PROS - the stock operation modes are more or less kept; IM - PCV sucks in gas, bringing fresh air through the breather at part-throttle
CONS - at WOT, when there is maximum blowby, all that gas can escape only through the breather which (depending on engine and boost level) might not be enough
Option 2
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Simply vent both the PCV and the breather line to atmosphere; replace PCV valve with a straight fitting. Use oil catch cans and breather filters.
PROS - blowby escapes through both routes at all times
CONS - fresh air isn't brought into the crankcase. The hydrocarbons from the blowby can react with the oil and change its properties.
Option 3 - Recommended for high boost
![]()
Basically like option 2, except that the stock pathways are blocked off in favor of bigger ports which allow greater flow.
PROS - blowby can easily escape through the oversized fittings and large catch can
CONS - fresh air isn't brought into the crankcase. The hydrocarbons from the blowby can react with the oil and change its properties.
A certain amount of gas, known as 'blowby gas', escapes around the pistons while the engine is running. PCV, Positive Crankcase Ventilation, is a system that allows venting of this hydrocarbon-rich gas out of the crankcase.
A N/A PCV setup is usually looks like this:
The breather is simply a straight-through fitting, while the PCV valve is a special valve which is closed when there is too much pressure difference on its ends, in this case when there is too much vacuum in the IM (e.g. at idle). There are different ways in which this system vents gases:
1) At idle, the PCV valve is fairly closed, so the majority of the little blowby gas escapes through the breather.
2) At part-throttle, the PCV valve is open and the vacuum from the IM sucks gas out of the crankcase; fresh air is brought in through the breather
3) At wide-open throttle, gases escape through both the breather and the PCV valve
Unfortunately, this setup cannot be used if you are turbocharging your vehicle; the boost will leak though the breather (and even PCV depending on the valve) and pressurize the entire crankcase; the blowby won't have anywhere to escape..
Option 1 - Recommended for low boost levels
Keep the idea of the stock system, but breather goes to atmosphere instead of intake; an oil catch can is added to catch any oil coming out of the breather; the can also has a filter to keep junk out of the crankcase. An oil catch can is added between the IM and PCV valve, and - most importantly - a check valve which closes off whenever there is boost in the IM, avoiding any boost leak into the crankcase.
PROS - the stock operation modes are more or less kept; IM - PCV sucks in gas, bringing fresh air through the breather at part-throttle
CONS - at WOT, when there is maximum blowby, all that gas can escape only through the breather which (depending on engine and boost level) might not be enough
Option 2
Simply vent both the PCV and the breather line to atmosphere; replace PCV valve with a straight fitting. Use oil catch cans and breather filters.
PROS - blowby escapes through both routes at all times
CONS - fresh air isn't brought into the crankcase. The hydrocarbons from the blowby can react with the oil and change its properties.
Option 3 - Recommended for high boost
Basically like option 2, except that the stock pathways are blocked off in favor of bigger ports which allow greater flow.
PROS - blowby can easily escape through the oversized fittings and large catch can
CONS - fresh air isn't brought into the crankcase. The hydrocarbons from the blowby can react with the oil and change its properties.
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