Valve Cover Vents

[John Fitzpatrick]

I saw a Shelby GT500 at a car show last weekend and the guy had an AN elbow w/ braided steel line running from the valve cover down somewhere out of sight. I thought this was just used on dry-sump engines, which this wasn't. Is there an advantage to this or was it just for show?

 

[Jim S.]

John,

This is done frequently on drag cars. Those hoses are running down to a oneway valve attached to the header that creates a pressure drop to draw crank pressure out of the motor. Usually on motors that have cams with a larger amount of valve overlap, therefore they have very little manifold vacuum to relief crankcase pressure Via PCV Valve.


Cheers

 

[Jac Mac]

Sounds like the car you observed had the setup as described by Jim, also was done on wet sump Trans Am boss 302,s to help drain the rocker covers on long fast turns and is quite common on wet sump circle track cars on the RH-(outer) rocker cover.
The exhaust scavenge type breather is banned by several sealed track organisations as if the engine lets go big time and the driver attempts to get back to the pits a large amount of the oil will be dumped on the race surface rather than remain in the catch tank. It works in a similar manner to an efficient dry sump by lowering the pressure in the crankcase, real handy when running in restricted type class's.

Jac Mac