I'm looking into a way to run my PCV lines with my turbo build. Using a catch can and routing it up like everyone does I am seeing a flaw in the design. Under normal operation, there is un-metered air entering the engine...

Let me explain. On an oem setup, the air inlet has the PCV line to the exhaust side valve cover plumbed "After" the MAF. This air is pulled through the engine and into the intake manifold and is metered by the MAF so not to run lean. On a turbo, you don't run the line into the charge air pipe, you go into the inlet pipe going right into the turbo inlet. This means that under light load/idle conditions, the pcv system is sucking un-metered air through the engine and into the intake. Only under load when the pcv systems works backwords would this be ok because it all gets sucked into the charge pipe and is metered by the MAF before going into the engine.

You don't want to just not hook up your pcv line to the inlet. You want your crankcase pressure relieved under heavy load. So it needs to be there. But at all other times, the system is letting air through the system and into the intake un-metered.

Hopefully this makes sense and someone can make a suggestion.

 

All I can come up with is just venting the crankcase to atmosphere. Run both valve cover ports to a catch can with a breather on it and plug the intake port that was for original operation. I no longer have a way for the air from pcv system to be accounted for by the MAF. I don't think there is any harm to the engine by doing this. As long as there is an opening, pressure will escape. It cant just hang out in the engine as long as there is an opening to expand through.

 

Yeah why won't you vent out the one of valve covers with AN fittings and bungs weled to it and nice braided hoses to catch can that vent out the nasty stuff to the atmosphere. Hot oil/air vapor from crankcase always seeks it's way through to the top of motor. Venting out from the valve cover to catch can with breather to atmosphere is absolutely the best way.

 

In my experience, any turbo motor with lots of boosts will eventually need this setup. I don't know your ring condition or bottom end was rebuilt fresh or what not but trust me you won't cut it with factory PCV system when you go boost. You will need this setup when you are making a lot of boost eventually anyways.

 

MAf isn't worrying about your pcv gas that coming through. It's located at before all that anways. It's your tune with standalone ecu that adjusts the air/fuel by MAF. What kind of ecu or tune are you planning to run?

 

Not in this case. I can see why speed/density setups wouldn't have this problem, but with a MAF and o2s it is. I'll explain again because it is confusing. The MAF is in the charge pipe. You cant run your PCV from a turbo charge pipe. PCV would have to be drawn from the turbo's inlet pipe. This is before the MAF. It would draw air through the engine and to the intake without passing the MAF. The A/F mix would be picked up by the o2s as lean. I feel this would make tuning the car difficult because at all times, all different vacuum amounts etc, there would be an inherent lean condition. No matter what you tune for, there is an unmetered air source coming in to worry about.

The only reasons I'm having a second thought is that I still prefer having a vacuum source pulling the vapors from the engine rather than them just festering and coming out as they please. Seems like the engine would be more prone to sludge. I think I just have to accept running the lines to a can with a breather. Nothing extravagant is needed. Just two hoses from both valve covers to the can.

I am running a piggyback ecu by the way. Apexi AFC Neo.

 

Yes just delete your factory PCV system and run the catch can and vent the pressure out. I wouldn't worry about the sludge built up.

 

If you are looking for a vacuum based system have you looked into dumping it into the exhaust as another option? I have seen a few Supra's run this way also:

https://ls1tech.com/forums/advanced-...u-exhaust.html

On my Supra I just vent it to atmosphere with dual an10 lines to a baffled catch can but I prefer to run it this way as my preference. No problems and no fumes or smells.

 

Did you delete your factory PCV setup?

 

Yes but only because everything is mostly aftermarket under the hood. I still run the factory baffles in the stock valve covers but I just tapped in two an10 fittings.

If you ever decided to get aftermarket valve covers, I would stay away from ones that have the an fittings all the way in the back near the firewall because your oil catch can will fill up faster than where the normal vent location is now.

 

Ideally u want to pull vacuum on the crankcase if you don't want to end up with a leaking front main. Seen it blow out front main 3 times on a friends car that he believed pulling vac didn't matter, after he kept having leaky front main I convinced him to hook it to the turbo inlet and no more issue, that was 8 years ago, car still good and now he believes.

There are plenty of people running cans with just a filter on it to atmosphere not pulling a vacuum, and it's usually fine with no issues other than a light oily mist covering the hoodliner and engine bay if your into that. I don't do it on the bays I build because you want a vacuum on the crankcase, it helps seals the rings which reduces friction which can make more power as rpms increase as well as help control oil consumption (on top of eliminating pressure against the front/rear seal).

You are overthinking the maf situation. It won't effect it. If the car is keeping the maf for piggyback I always move these vvti MAFs to blowthrough on cold side of intercooler on single turbo setup and there are never any issues. The maf doesn't care what the air is or what i consists of, the gs/aristo hotwire mafs are just measuring the temperature of the wire and the temp of the air beside the wire, when a higher volume (throttle open) of air passes over the wire it starts cooling the wire down and the ecu needs to raise the voltage to the wire to make the wire heat back up to the regulated temp and this differential in voltage is your maf signal back to the ecu that it calculates your fuel delivery from (maf signal used in conjunction with the 02 reading of course).

So point being it doesn't matter what is passed over the maf wire, it is just how much of it is passed by it, it could be outside air, argon, or hot wet farts. The 02 sensor will take care of understanding the content left after the burn. The only minor concern of routing a catch pre-maf is over time the possibility of oil mist build up on the hotwire, which I've never seen be a problem on a healthy motor. And if once a year or so you needed to spray some maf cleaner on the wire to clean it isn't a big deal.

A healthy motor is barley producing anymore than a fine light mist under full rpm anyway. After 10,000 miles I only get about a shotglass worth from draining the catch can and the intercooler pipes/maf were clean. It's mostly condensation that the catch can will fill up with anyway and that comes from start up, it's not oil. The catch can just produces a oily yellowish water, if you are getting a catch can full of actual oil then you have problems.

A REAL catch can design that has heavy proper baffling is of the utmost importance though! An empty can or can with a **** baffle design is useless, might was well just hook the covers to the turbo with no can at that point.

If you want the catch can operate even more efficiently to keep the least amount of blowby to enter the turbo, mount it outside of the engine bay such as behind the bumper, this major temperature difference outside of the hot heat soaked engine bay will improve the dew point and help drop oil/water out of suspension more thoroughly in the 'cold' can.

At the end of the day, just run both covers to a baffled can and can to the turbo intake, no pcv valve. And get a good nights sleep.

 

I guess it’s better to have it run to the turbo inlet at least so it pulls the gases under heavy load when pressure is high. Thanks for the suggestion