Re: [T3] Distributor and breather box questions

["joshua brooks" <joshua_bro@msn.com>]

    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
 

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