Several years back (on the old forum), I learned of a fixed orifice PCV valve used on the LS engines that would also fit the L31. This info was provided in a post by NJCKZ71:

"Replace the L31 PCV valve with the fixed orifice unit and thank me later - P/N 12572717"

I wish he was still around here, as he was one of our resident engineers and an extremely smart guy. I learned a lot from his posts, which is why I copied and pasted many of them into Wordpad documents for later reference (this PCV valve, case in point).

So, I looked into it since the PCV valve in my mom's 99 Tahoe was buzzing. Thought this would be a good time to try this out. As to GM's reason for doing this, here is some background on the fixed orifice valve:

www.mightyautoparts.com/pdf/articles/tt122.pdf

Procured one of these along with a stock L31 valve (both in AC-Delco as those are the ONLY PCV valves I use) from the local Delco distributor and took a few pics before the install:












So far so good. Everything seems fine, but I will be keeping an eye on oil level to track any possible consumption change or other effects. I was wondering if anyone else here has tried this, and if so, what is the verdict?

I'm thinking, that's a very small orifice...

L31 manifolds have a hole in the floor of the manifold near the CPI block that goes right into the valley. With the existence of that I would think the PCV valve and associated tubing could be omitted and crankcase ventilation retained.

James, are you saying that you could do away with the PCV all together?

TJ

I believe you want to have air circulated through the crankcase. That helps draw the moisture and such out. Just removing the blowby gasses alone wouldn't provide a sufficient effect.

I'm not certain you could create enough of a vacuum in the crankcase using a one sided pcv system like they use in high HP applications that have an external air pump for this.

I can't speak for the chevy, because I don't have one in front of me and can't remember how its done... but on the stuff I work on commonly, there is a large hose connected to the intake duct in front of the throttle plate and to one valve cover, and two smaller hoses (one from each valve cover) connected after the throttle plate to draw the air through the crankcase. There are metered orifices on both of those small hoses, but they are very small and often plug up with carbon after a couple years, neccesitating removing the breather covers, cleaning and resealing them.