PCV under boost
04-30-2010, 03:32 AM
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PCV under boost I’ve a 1999 supercharged Corvette running 6 psi. I need some advice as to how to remove crankcase pressure. It’s a 1999 so the PCV valve is routed down the side of the valve cover – it’s not in the valley like in later models.
The current set up is as follows:
The valve cover breather tube (passenger side at the front) is closed off at the throttle body and re-routed to a position before the supercharger, so that clean air can enter the crankcase. That works OK.
The PCV valve goes into the manifold as per the stock arrangement. My problem is that once in boost the PCV valve will shut (as if a backfire on a stock set up) and the crankcase pressure will build up from blow-by, so there is no where for the pressure to go. Just when you need to relieve the pressure - the PCV shuts.
The valve cover breather arrangement (above) has a one way valve combined with a catch can so that under boost it shuts (clean air can enter under vacuum but under boost it shuts so it can’t escape). Thus under boost there is nowhere for the pressure to go – it can’t even escape via the valve cover breather.
So how do you vent the crankcase under boost? There seem to be a number of options:
1. Live with it.
2. Put in a breather on the crankcase or oil filler tube (and live with the vacuum leak)
3. Put a catch can after the PCV valve and route to manifold (but the PCV will still shut under boost)
4. Put a catch can after the PCV valve and route to the intake before the supercharger. (This requires blocking off the manifold intake)
5. Put a catch can after the PCV valve and route to atmosphere - naughty. (This requires blocking off the manifold intake)
6. Throw away the PCV valve and put in a catch can and route to intake or atmosphere (as 3 & 4 above).
Do you need a one-way valve in any of the catch can scenarios?
Do you need both a catch can and a PCV valve – are they alternatives, or used in combination?
See why I’m confused.
Which one do you recommend, given that I don’t want to convert to the Z06 or later versions, not do I want to opt for the small orifice PCV version?
The current set up is as follows:
The valve cover breather tube (passenger side at the front) is closed off at the throttle body and re-routed to a position before the supercharger, so that clean air can enter the crankcase. That works OK.
The PCV valve goes into the manifold as per the stock arrangement. My problem is that once in boost the PCV valve will shut (as if a backfire on a stock set up) and the crankcase pressure will build up from blow-by, so there is no where for the pressure to go. Just when you need to relieve the pressure - the PCV shuts.
The valve cover breather arrangement (above) has a one way valve combined with a catch can so that under boost it shuts (clean air can enter under vacuum but under boost it shuts so it can’t escape). Thus under boost there is nowhere for the pressure to go – it can’t even escape via the valve cover breather.
So how do you vent the crankcase under boost? There seem to be a number of options:
1. Live with it.
2. Put in a breather on the crankcase or oil filler tube (and live with the vacuum leak)
3. Put a catch can after the PCV valve and route to manifold (but the PCV will still shut under boost)
4. Put a catch can after the PCV valve and route to the intake before the supercharger. (This requires blocking off the manifold intake)
5. Put a catch can after the PCV valve and route to atmosphere - naughty. (This requires blocking off the manifold intake)
6. Throw away the PCV valve and put in a catch can and route to intake or atmosphere (as 3 & 4 above).
Do you need a one-way valve in any of the catch can scenarios?
Do you need both a catch can and a PCV valve – are they alternatives, or used in combination?
See why I’m confused.
Which one do you recommend, given that I don’t want to convert to the Z06 or later versions, not do I want to opt for the small orifice PCV version?
