crackcase vent filters??

xsnapshot

Think about what your saying for a second. "70% of blowby gasses are unburnt hydrocarbons". I'm not sure where you came up with that number as it's likely NOT true. What about all the other non-hydrocarbon gasses that are present? The overwhelming majority of combustion gasses would be non-hydrocarbon gasses. Anything not consumed during combustion will be very minimal. However let's assume it is true.

70% of the blowby gasses (which is a small amount to start with) gets sucked back into the intake tract. Want to guess how much %-wise this unburnt hydrocarbon mixture is vs amount of fuel injected into the cylinder during combustion? Basically negligible. The ECM has NO WAY of measuring this. Your mass airflow sensor tells the engine how much air is getting in through the intake and thats ALL the ECM injects for. So yes I am saying that NISSAN does not account for blowby gasses in the AFR equations. I can also tell you for certain that Subaru does NOT account for blowby gasses in their modern ECM's as well. I have a fair bit of experience working with Opensource tuning on the Subaru's and have seen the effects of running crankecase breathers set to VTA on aggressive and daily driver vehicles. In short there are no problems (at least with AFR anyway...emissions is another story). I'm not as familiar with Mitsubishi, but I'm pretty sure they don't account for it either.

The ECU's AFR correction is also not 3D. Its 2D. Think of it like this. (just guessing on the actual g/s values)

MAF sensor g/s ECU correction %
0-10 x%
11-30 y%
30-50 z%
50+ a%

Oil contamination is not really a concern. The oil gets really hot and the fuel is vaporized. Even with just VTA crankcase breathers, you should really be fine unless you never let your engine get up to operating temps. If anyone is really that concerned about fuel dilution then get an oil analysis done after your first oil change of running VTA breathers.

Also an AFR and an O2 sensor are one in the same. In fact there is no such thing as an AFR sensor. The O2 sensor just measures the ratio of oxygen in the exhaust tract to that of the ambient air. Then calculates the air fuel ratio based on that data.

Additionally your comments about the air filter and the manifold not delivering the same amount of air is meaningless. Only air that makes it past the air filter will be measured by the ECM (which then tells the injectors how much to inject), and all of that air will go into the engine to be burned. Perfect air-Cylinder distribution is inconsequential because there is not an O2 sensor at each cylinder. The system's O2 sensor is only being read far enough downstream that cylinder exhaust will be mixed. I would agree that air-cylinder distribution is important, but its not adjusted for in the ECM.

I'm glad you've had good luck with your setup. I'm not saying all of what you said was miss-information, just the part about the ECM using blowby as part of the air fuel equation.

6SPD_FTW

I've never personally analyzed blow-by gases like the EPA has, so I don't know for a fact. I have read in several places that blow-by is mostly unburnt fuel - and the 70% figure is what was attached to those statements. The flame front extinguishes itself as it gets close to the relatively cool cylinder walls, aka, barrier layer. If that layer does get burnt, you overheat and melt pistons. Blow-by is mostly hydrocarbons because the piston rings (hopefully) never actually get exposed to the by-products of combustion until the exhaust stroke. The rings and cylinder walls are protected on the power stroke by that boundary layer of unburnt fuel and air...which is what would be blowing right by the rings. Blow-by shouldn't be exhaust by-products unless it's happening on the exhaust stroke. If exhaust gases are leaking passed rings on the power stroke, you got some real serious problems and probably a few pistons with holes burned through them.

The ECM has no way of monitoring PCV flow....I know this. As far as it being figured into the base fuel map, all I know is Toyota must be more advanced that Nissan or Mitsubishi or Subaru because Toyota ECM's DO factor PCV flow into fuel delivery (particularly at idle and light-load driving). Toyota ECM's have no way to monitor PCV or modify it, however it is still factored into the base fuel schedule. I assumed Nissan...and all other manufacturers....would do the same. I suppose Toyota is ahead of the curve on that one. Nissan's, I suppose, just threw it on there and use the AFR sensor and feedback control to compensate for it.

And how is there no such thing as an AFR sensor? I thought it was a pretty common thing on vehicles these days. I know for a fact my 370Z has two of 'em. It also has O2 sensors too - two of them as well. I know because I've logged them before on Autoenginuity. The AFR's read 2.2V in closed loop and the O2 sensors read anywhere from 0-1V, depending on load.

Just having a VTA setup on the PCV is fine short-term. But without circulating some fresh air through there, it is absolutely impossible that all the water vapor, fuel vapors and oil fumes are going to do anything other than sit in the crankcase and contaminate the oil. Whereas if you leave it alone and install a catch can to prevent oil from getting siphoned through the intake, you get the benefit of knowing your oil isn't getting turned to sludge. I'm leaving mine alone because I plan on my Z lasting well beyond 200,000 miles on the original engine. Each to their own, but I don't think it's a smart idea.

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.

xsnapshot

6SPD_FTW, how does Toyota account for PCV flow with respect to fuel delivery? I'm just curious. I'd like to see how they estimate it.

6SPD_FTW

http://www.autoshop101.com/forms/h63.pdf

Details as to how they factor it into the feedback control I do not know. But I'm certain there's a calculated flow rate and specification for the PCV valve on each engine. PCV flow at X inHg vacuum is a known constant for every valve. I don't think that's information anyone is going to be able to readily come by, though.

Late,
Trav

L33T Z34

Henry
I hacked the POS OEM plastic box to use the pipeing. I then just used the OEM 16mm vac hose, slightly twisted it downward and attached the 5/8" K&N crank case breather. Plugged the OEM intake rubber accordian hose w/1/2" pipe plug from Home Depot. Very easy job.
LOL! I got a good laugh from 6SPD FTW intake theory!

henry0844

I lost track of this thread, then pop! here it is again a year later lol. got the g3s instead but thanks for the response