Another Pcv question
08-21-2009, 06:06 PM
#1
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Another Pcv question Ok put on new tsp heads almost 10,000 miles ago car runs fine within last mont put on some aftermarket valve covers no pcw gromments well lately found oil on threads not a valve cover leak trust and at high rpm i hear a hissing sound my question is will no pcv cause oil to blow by rings or down valve seals havent noticed any smoke at start up or accleration but fews times when letting out of it
08-21-2009, 07:29 PM
#2
You need some kind of venting for the crank case, a pcv would be the best choice because it sucks out crank case gases. At the least a breather on the oil fill cap will help. What did do with the stock pcv when you installed the new rocker covers?
08-21-2009, 08:25 PM
#3
Ok put on new tsp heads almost 10,000 miles ago car runs fine within last mont put on some aftermarket valve covers no pcw gromments well lately found oil on threads not a valve cover leak trust and at high rpm i hear a hissing sound my question is will no pcv cause oil to blow by rings or down valve seals havent noticed any smoke at start up or accleration but fews times when letting out of it
We've actually picked up over 5hp across the board average (nearly 20hp at peak) by adding a vacuum pump to the PCV and pulling approximately 20inHg constant vacuum at WOT. Most rings seal much, much more effectively when they have vacuum behind them.
With pressure behind the rings, none I have ever seen can maintain a good seal against the cylinder wall.
This condition allows oil into the combustion area, and allows combustion pressure to blow-by the rings into the crankcase...creating even more pressure as well as contaminating the engine oil with combustion byproducts.
Do yourself and your engine a favor, plumb the PCV properly. Replace the valvecovers if that what it takes, they might look spiffy but they're costing you power and engine longevity.
08-23-2009, 07:04 PM
#4
Crankcase pressure wants to get out. If it can't escape at the PCV it looks elsewhere. The PCV spring tries to hold the valve open to relieve pressure. The crankcase pressure tries to push it shut and the intake tries to suck it shut with vacuum. If the crankcase pressure or intake vacuum are stronger than the PCV spring the valve will go closed. At high engine speed(RPM)-heavy load your vacuum is low so the spring wins the battle and there is good PCV flow. At idle speed-lite load the vacuum is highest so the spring loses the battle and the PCV closes(little or no flow). In between the PCV valve is somewhere between open and closed depending on vacuum and crank pressure. The spring tension is constant. The PCV can get stuck open or closed if not maintained.
