[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [New Search]
One problem with adding the vents to the heads is that most people don't understand that the 72-73 vents were part of the PCV SYSTEM. They aren't actually outlet vents but inlet vents. On the earlier cars The breather does nothing but allow air to escape. The air is either vented to the atmosphere or the aircleaner where it is burned with the intake charge. In the PCV system the case breathes through a PCV valve wich lets pressure in the case out but won't let low pressure pulses draw air in. From the PCV valve the air is routed through a hose to the intake plenum. So the case has manifold vaccum pulling on it wich causes clean air from the aircleaner to be drawn into the vents on the heads, through the pushrod tubes and crankcase and eventually into the intake plenum. Some of the advantages of this more complicated setup are. 1. A cleaner engine. Instead of hot dirty combustion air from blow by pushing more dirty combustion air out of the case, giving all of the carbon and other contaminants a chance to settle or burn onto surfaces inside the engine, the blowby air is mixed with clean air and pulled out of the engine. 2. Efficiency. Although any advantage is probably slight The pistons have less air resistance in a lower pressure case. The basic reason cumbustion moves the piston is pressure is greater above the piston than below. Lower crankcase pressure makes this more so. 3. A cooler engine. That cool air being pulled through the heads absorbs heat from the inside of the engine. 4. Prevention of oil leaks. A crankcase with lower internal pressure is less likely to leak oil and the severity of any leaks from the case is likely lower. I have also heard that in a VW in hard cornering. A PCV system will pull oil that sloshes into the valve covers back toward the case. I don't know if it has been tested though. Oddly enough the only type3 manual I have seen that covers this is the Clymer. The Bentley doesn't cover it. The Clymer has a nice diagram of the system operation and flow. One reason I like to think more books is better. The Bentley is indispensable but also imperfect. Josh Brooks ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~