what to do about pcv valve from boost
08-18-2004, 08:29 AM
#32
0.0 BAR
Join Date: Aug 2004
Posts: 3
Re:what to do about pcv valve from boost
Originally Posted by Whitey
Alright kids this is what I do about the PVC system. The system on the back of the block is fine and doesn't need to be fucked around with. For the valve cover breather buy one of these things;
http://static.summitracing.com/globa.../mor-25900.jpg
Its a crankcase evac kit. This thing is for a V8 so there's twice as many parts as you need. But it basically uses your exhaust to pull a vaccum out of your block. V8's have been using these things for years.
Here's a basic rundown of the parts
Than all you do is run a hose from your valve cover to the fitting that is now welded on the exhaust. If you have a cat weld this on after the cat. This system is simple and effective
http://static.summitracing.com/globa.../mor-25900.jpg
Its a crankcase evac kit. This thing is for a V8 so there's twice as many parts as you need. But it basically uses your exhaust to pull a vaccum out of your block. V8's have been using these things for years.
Here's a basic rundown of the parts
Than all you do is run a hose from your valve cover to the fitting that is now welded on the exhaust. If you have a cat weld this on after the cat. This system is simple and effective
04-04-2005, 03:36 PM
#39
0.0 BAR
Join Date: Nov 2004
Posts: 17
Re: what to do about pcv valve from boost
This thread shows 2 different setups, 1 setup with the breather element, the PCV is likely always working in the high vacuum range, means low PCV recirculation all the time. While in setup 2, PCV is always working in high circulation mode, or if you are unlucky, 0 vacuum leads to blocking PCV.
Basically, it works on the difference in vacuum between intake and intake manifold. Take a minute to understand that this difference is also how people measure load of the engine. Low vacuum difference = high load (WOT), high vacuum difference = low load (TB closed). Also note that under all conditions, vacuum pre TB is always higher than post TB, it is just a matter of high or low.
Now, physics tells us that when vacuum difference between intake and manifold is high, air will take alternative path through the crank case into the intake manifold. Without the PCV, during low load, high amount of air will take another route due to high vacuum, and vice versa. This is counter intuitive because we want maximum circulation during high load.
So, PCV valve is put in to "reverse" the bahavior, as below
if vacuum is -ve : Reverse flow situation, intake manifold has higher pressure than intake, PCV blocks. (this never happens in NA anyway)
if vacuum is 0 : Engine's off, or instances where both vacuum and intake manifold are of the same pressure. The PCV blocks.
if small vacuum : High load condition, maximum PCV bypass
if high vacuum : Low load condition, small PCV bypass
if very high vacuum : PCV blocks (condition of back fire, causing temporary pressurized crankcase, PCV blocks to prevent fire from reaching the intake manifold)
As you can see, on both end of the range of vacuum, PCV blocks, and it is best to design your system such that during low->high boost/throttle, the vacuum difference works in the range of slight vacuum to some high vacuum level.
Basically, it works on the difference in vacuum between intake and intake manifold. Take a minute to understand that this difference is also how people measure load of the engine. Low vacuum difference = high load (WOT), high vacuum difference = low load (TB closed). Also note that under all conditions, vacuum pre TB is always higher than post TB, it is just a matter of high or low.
Now, physics tells us that when vacuum difference between intake and manifold is high, air will take alternative path through the crank case into the intake manifold. Without the PCV, during low load, high amount of air will take another route due to high vacuum, and vice versa. This is counter intuitive because we want maximum circulation during high load.
So, PCV valve is put in to "reverse" the bahavior, as below
if vacuum is -ve : Reverse flow situation, intake manifold has higher pressure than intake, PCV blocks. (this never happens in NA anyway)
if vacuum is 0 : Engine's off, or instances where both vacuum and intake manifold are of the same pressure. The PCV blocks.
if small vacuum : High load condition, maximum PCV bypass
if high vacuum : Low load condition, small PCV bypass
if very high vacuum : PCV blocks (condition of back fire, causing temporary pressurized crankcase, PCV blocks to prevent fire from reaching the intake manifold)
As you can see, on both end of the range of vacuum, PCV blocks, and it is best to design your system such that during low->high boost/throttle, the vacuum difference works in the range of slight vacuum to some high vacuum level.
