vacumed pcv?---question

[stroker_valiant]

This is a setup I saw at a recent car show, 66 Dart, 340 based stroker. Is the breather tube out of the valve cover plumbed into the exhaust for a vacuum effect? What are the benefits of doing this? I’m just curious; I have never seen this setup before.

 

[toolmanmike]

It's a race engine thing. Vac-u-pan is what it is called. The exhaust flowing through the headers creates a vacuum to suck the blow by out of the engine.
Engines with lots of compression and cylinder pressure build a lot of pressure past the rings and valve stems into the crankcase. A normal single breather cap and pcv system can't keep up. Mike

 

[stroker_valiant]

Ahhh, ok, that makes sense. This motor has to run high octane fuel, so high comp. it is. Thank, that clears it up!

 

[ramcharger]

The reason this style of breather is used in racing is that there is little vacuum in the intake manifold under WOT conditions to evacuate the crankcase when it needs it the most.

Tranversely, this system pretty much does nothing under street conditions where a positive crankcase ventilation system works at peak efficiency.

The third option is a belt driven vacuum pump that pulls vacuum under all conditions. Of course a special made valve cover set up is needed for this and it's not cheap.

 

[fishy68]

Also note that a pan-evac doesn't work if you run full exhaust. Any back pressure will pretty much make it useless.

 

[stroker_valiant]

Awesome, thanks for the info, that clears it up well.