crackcase vent filters??

xsnapshot

Both of those sensors you described are O2 sensors. One is wideband, and one is narrowband. Both measure the ratio of oxygen in the exhaust stream, however only the wideband is capable of reading a "wide" range of values accurately. Whereas the narrowband oxygen sensor is only capable of reading (and is accurate too) the small region surrounding stoichmetric. This is basically to monitor the effectiveness of the catalytic converter, and the ECU ignores it's reading during WOT/open loop operation. AFR is calculated by the ECU from the voltage delivered by the O2 sensor. People commonly refer to them as AFR sensors, when really they are O2 sensors. That is all they are "sensing".

I do agree on the boundary layer phenomenon though. That makes sense. I would still be hesitant to believe the 70% figure, but taking that boundary layer into effect makes it more believable.

You have to remember that blowby not only contains unburnt hydrocarbons, but also unused oxygen. So its not as if your directly adding fuel alone. If the blow by mix is similar to the mix the ECU is targeting for the burn, then you would not need to account for it, although it is present.

I would also agree that a VTA crankcase will have higher levels of fuel/water/etc present in the oil over a Crankcase that has a vacuum pulled on it. To what degree the levels increase, is what I would be interested in knowing. In my opinion its probably not a significant increase.

Personally I would not run VTA, as even the best flowing filter still causes a restriction. I would run vacuum line with a check valve to a fitting welded in the exhaust stream in the direction of exhaust flow, and rely on the Bernoulli effect to pull a vacuum on the crankcase. Since velocity would need to be relatively high, and Back pressure relatively low, I would only do this with an aftermarket exhaust where the restrictive muffler is free flowing.