Crankcase breather catch cans

I have actually used a single modified pcv valve as a crankcase vacuum source for over 10 years now. Street driven 355sbc that occasionally sees 8600rpm, but with a sealed crankcase that does not draw external air. Engine is sealed up pretty good, not much actual flow velocity to carry oil out of the engine. Currently don't use any catch tank between the engine and pcv valve. Used to have one, but experience showed that one was not needed in my application.

With a pcv valve drawing the vacuum with a sealed crankcase, I can tell you my crankcase vacuum does not drop to "0" instantly when you go full throttle. I have a log showing pcv supplied crankcase vacuum starting out at 12.6"Hg, then after 6.25sec of full throttle the crankcase still had 3"Hg left. Takes some time to draw it down.

So my question for you guys to ponder is, how long does one actually need the vacuum in a street/strip crankcase to last? If my car does mid 5's in the 1/8th, do I really need more than 3"Hg of vacuum after 6.25sec of WOT? How often am I going to use more than 6sec of WOT on the street? For me only if i'm testing on a backroad somewhere, don't need that much time to merge on a freeway or pass someone.

Another thing to ponder- the more overall crankcase volume your engine has, the longer it will take to draw pcv valve supplied crankcase vacuum down. Bigger oil pans can add volume, as can tall valve covers. There is also the option of adding external volume, such as oem plastic vacuum reservoirs. If you have a pretty serious car that requires a big catch tank for the breathers, that big catch tank itself could be configured to add crankcase volume by putting check valves inside the breathers.

My personal example is just a street/strip toy, but having lived in the 60s/70s I really like the gasser look. With no front bumper on my car, it's really screaming for a Moon style tank up front. But i'm also against adding something to my car that isn't functional. An extra fuel tank up front for a car that runs nitrous on pump gas isn't something I need or want. Don't need the extra weight of fuel up front, probably not the safest thing on the street either. What I've decided to justify the tank up front to myself is to use it as a catch tank for the crankcase. Plumb it to the valve covers with big hoses, and move my check valve breathers and pcv valve to the tank. A normally empty aluminum tank won't add much weight up front, but it will effectively add quite a bit more volume to my crankcase. Don't really need it, but to me the experimental aspect is enough to justify adding the tank :)

In my case I do not need a Wagner valve, a modified stock pcv valve works just fine.

Grant