valve cover breathers ??
Thread Starter
Drifting
Joined: May 2001
Posts: 1,392
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From: Wabash,IN
CI 7-8-9-10 Veteran
St. Jude Donor '08
valve cover breathers ??
This may be a dumb question but what is teh purpose of theses? I have seen them on many cars jus wandered why and what they are suppose to do. Thanks jay :crazy:
Le Mans Master
Joined: May 1999
Posts: 6,519
Likes: 1,305
From: Windermere FL
Re: valve cover breathers ?? (jparr)
These breathers are used to filter the air sucked thru the PVC system. On stock cars, the air come from a tube off the throttle body. I added a breather when I changed valve covers and could not find a fitting to adapt the existing tube to the new hole.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Re: valve cover breathers ?? (jparr)
Ah, yes, the ole breather issue again.
Here's the deal.
As an engine operates a certain amount of combustion pressure gets past the rings and into the crankcase (oil pan, block cavities, etc.) Without a way out, in a short time, this builds pressure which must be relieved or it will build to a point of pushing out one or more of the gaskets. Leak time.
Visualize blowing air into a balloon; if you keep blowing at some point something's gotta give.
Even worse, pressure can build so high that it actually begins to work against the piston as the piston begins its intake and power strokes. The pressure can overcome the sealing ability of the rings and case a major loss in power too.
An inadequately vented engine's oil pan can actually been seen to expand on the dyno; just like air in a balloon expands the balloon material.
So a system was devised to vent the pressure build up. Before the emissions days, the pressure was simply vented to the atmosphere, but that pollutes, so the PCV system was designed. PCV stands for Positive Crankcase Ventilation, and that's what it does. It lets the pressure get recycled into the intake system where the gasses are mixed with the fresh air/fuel charge and burned. It also relieves the pressure buildup, but only to a point.
Once your engine beings to make big power or is run at high RPMs, the PCV system can't keep up and the pressure builds again. Power adders, like superchargers, compound the problem by the mere fact that they allow greater amounts of air into the engine to make more power.
Another factor that hurts the PCV system is that it depends on engine vacuum to work properly. So once you're on the floor, engine vacuum drops to close to zero and there's not enough vacuum present to allow the PCV system to vent the engine.
On a L98 there is a second venting hose on the passenger side of the engine which is supposed to allow venting to continue even when vacuum drops off during WOT, but it, too, is marginal.
Most dedicated races have now gone to a vacuum pump system to vent their engines as opposed to the 'old days' way of running a hose from each valve cover to a fitting welded onto the header collector.
Hope this helps.
Jake
Here's the deal.
As an engine operates a certain amount of combustion pressure gets past the rings and into the crankcase (oil pan, block cavities, etc.) Without a way out, in a short time, this builds pressure which must be relieved or it will build to a point of pushing out one or more of the gaskets. Leak time.
Visualize blowing air into a balloon; if you keep blowing at some point something's gotta give.
Even worse, pressure can build so high that it actually begins to work against the piston as the piston begins its intake and power strokes. The pressure can overcome the sealing ability of the rings and case a major loss in power too.
An inadequately vented engine's oil pan can actually been seen to expand on the dyno; just like air in a balloon expands the balloon material.
So a system was devised to vent the pressure build up. Before the emissions days, the pressure was simply vented to the atmosphere, but that pollutes, so the PCV system was designed. PCV stands for Positive Crankcase Ventilation, and that's what it does. It lets the pressure get recycled into the intake system where the gasses are mixed with the fresh air/fuel charge and burned. It also relieves the pressure buildup, but only to a point.
Once your engine beings to make big power or is run at high RPMs, the PCV system can't keep up and the pressure builds again. Power adders, like superchargers, compound the problem by the mere fact that they allow greater amounts of air into the engine to make more power.
Another factor that hurts the PCV system is that it depends on engine vacuum to work properly. So once you're on the floor, engine vacuum drops to close to zero and there's not enough vacuum present to allow the PCV system to vent the engine.
On a L98 there is a second venting hose on the passenger side of the engine which is supposed to allow venting to continue even when vacuum drops off during WOT, but it, too, is marginal.
Most dedicated races have now gone to a vacuum pump system to vent their engines as opposed to the 'old days' way of running a hose from each valve cover to a fitting welded onto the header collector.
Hope this helps.
Jake
