Popular subject going on a couple message boards; there is an idea boosted by the 'copy a racecar' type that maintaining some high level of crank vacuum is 'better'. Is it really? My thoughts:
The best way to avoid cank pressure IMO is to just 'let it go' instead of re-route. This applies for any dual purpose build.
When you re-route blowby to a suction source in order to not only accept this volume, but overcome it in order to create vacuum, extra check valves and restrictions from these lines need to be considered, and the volume of fumes removed must always be regulated vs. current engine conditions hp /crankcase flow. For legit 'racecars' this means buying the right size vacuum pump, gearing it to the right speed, having the right size lines running to it, and from it, to the right sized catch can to handle the exhaust, and having a regulator for your flow range installed, and fine tuned (for a given combination in good health).
- Complex YES!, could we make some version of this using only the engine, ...sort of.. Will it REALLY work? ehh..
- interest in steady supply of crankcase vacuum is a very common one, but without a separate vacuum pump produces no real tangible performance benefit.
- Any hp increase from potential ring seal improvement is by re-routing these fumes to the air intake is immediately offset by trying to make hp off of combustion gasses vs. all brand new air.
- Also consider to get this strong / tangible /measurable vacuum from some port between the main engine filter and the throttle body, there must be some restriction to cause this vacuum; The same restrictions you spend hundreds on, new or larger air filters, inlet tubing, throttle bodies to REDUCE this restriction. If you have measurable vac here, it is COSTING you hp already.
-Further, putting around the street with a functional pump in action will not get you to work faster or get you better mileage, the chic ks won't dig it either, but it will accelerate ring wear. Personally my most high strung cars still spend over 90% of their time, on the street, crusing, going the speed limit-ish.
Here is a video about fine tuning PCV flow I made which considers that 90%.