LEAVINU

So I recently swapped my stock valve covers over to some black Holley valve covers just for a cleaner look. The thing I noticed that I've never noticed before is there is a vent tube on the backside of the driver's side valve cover. From the factory it is capped but it made me ask why is it there in the first place and secondly why is it not venting to something like the passenger side head?

The answer I got back was that the LS1/6 had the PCV system through that port where as the LS2 PCV is via the valley cover. Ok, guess that makes sense but I still don't understand why cap it thereby providing not ventiliation to that side of the motor and only vent the passenger side head?

Another thing I heard is that in stock form the driver's side head is blocked from any circulation because of the valley cover. So, my question is has anyone added a breather on the driver's side vent tube to rectify this? Any ill effects to consider?

I saw a setup recently where the catch can was mounted on the brake booster and had an additional line to the driver's side valve cover. The passenger side vent tube was block and a filter was mounted to the oil cap. I'm thinking I may go this route as well but wanted to see if anyone else has done this?

haljensen

The PCV system is well thought out stock, don't try to out-think the engineers that designed it.

The fitting on the passenger side valve cover is not a "vent", it's a line to allow air INTO the crankcase. The PCV that removes oil fumes from the crankcase is a fixed orifice fitting at the front of the valley cover. The fitting on the drivers side you are talking about is capped because it's not needed, make up air is supplied to the passenger side valve cover and oil fumes are removed thru the PCV. It's a closed system that functions as designed.

LEAVINU

Why is it NOT capped on the LS7 then? It's T'd into a plastic hard line with the passenger vent.

haljensen

Big difference in plumbing between the semi-dry sump LS7 and the LS2 & LS3.

SUB VETTE

There's no reason you couldn't T into the other valve cover. Doing so would just provide another fresh air input to the crankcase (one through each valve cover). The valley cover still provides the exit path though which crankcase fumes, with the help of the inputed fresh air, exit and are ingested in the intake manifold through a hose or through a hose and catch can. Plugging the fresh air hose and opening the valve cover through a filter via the oil cap removes the "closed" PCV system and makes it an "open" to the atmosphere system which violates smog law rules. However, sometimes highly modified engines, especially forced induction systems, can produce more blowby and therefore higher crankcase pressures and builders go this route to keep pressure in crankcases from building up.

RussM05

Hal Jenson is 100% correct. Don't mess with it.

There is lots of information on the internet regarding PVC pumbing and why its done that way. But the bottom line is leave it alone if your car is stock or mildly modded. I personally have seem many systems mess with by the owners who believe they know more than the engineers but only succeed in causing a big vacuum leak and poor idle.

If you have a supercharger or turbo, there usually is a lot more blow-by which the stock PVC system can't accomodate so a additional vent is added to the oil filler cap. But if a picky state emission inspector sees that, he may fail your annual inspection.