Valve Cover breather with MAFT setup

[ScreamSalvation]

Ok, I've searched and read on the PCV system but haven't seen in definate answers for someone running a MAFT setup.

I know stock that the VC breather is hooked up pre turbo so it seems vacuum but never boost, correct? The PCV valve opens under vacuum but closes during boost, you would still be pulling out fumes through the VC breather.

Right now as some of you know I have been putting my eclipse back together from the PO and his mistakes. There is currently just a filter on the VC breather and the PCV valve is still hooked up. The car is also setup with a MAFT system on it.

I know the best way to hookup the VC breather would be after the MAF so that only metered air is allowed in, but being a MAFT setup that only leaves me hooking the breather to the intake manifold. This would allow the breather to see the necessary vacuum but also it would receive boost, thus possibley overpressurizing the VC, correct?

I guess it comes down to, with a MAFT, would the best setup be to connect the VC breather pre turbo again even with unmetered air and then richen the fuel mixture to account for this?

I plan on adding a filter or catch can to the PCV system and a check valve.

DSM link is hopefully in my future for tuning, but not this paycheck

 

[1992awdlaser]

Ive seen people completely plug up the Valve Cover breather and just drill through the pcv valve and only vent that. Seemed to work fine.

Ok. I thought you were trying to suggest to close up the side and the pcv location.

 

[SFRacingGST]

I asked this same question awhile back. First off adding a MAFT in a blow-thru set-up will create a major boost leak in non-boost conditions. The reason for this is that during these conditions, the PCV valve is open and is pulling fresh air from the VC port. When using a stock MAS, the VC port is routed back after the MAS, which would make it a closed system. After moving you MAS to the UICP, the system is no longer closed and the air that it pulls in from the intake will now be unmetered making it a boost leak. The way I solved this problem was putting a straight barb fitting on the VC instead ot a PVC (or drilling it out), and routing both lines to a catch can. I went one step further added another line from the catch can into the intake so the the vapors could be sucked back into the combusion. You can add larger ports to the VC if you are still having high crank pressure.

The factory setup is ideal. It pulls the crankcase pressure out under vacuum and under boost, and doesn't rely on the pressure finding a way out.

 

[TSIMonsteR]

Anybody know the thread pitch of the PCV port?

 

[Sam@RRE]

Sorry just had to pop in on this one. I read through half the first page and the first thing that bugged me is "positive pressure caused by the piston comming down". You also have to consider that another piston is going up as one is comming down. So that effect is canceled. The main reason MAFT and recirculation your blow by is the Hotwire element that the GM maf uses is very sensitive to oil contamination. Giving you inaccurate and false readings. The reason there is pressure in the crankcase is its getting past the rings because only in JDM world are rings and cylinders molecularly perfect and seal 100%.

 

[1992awdlaser]

I didn't mean to imply that everything the piston is pushing down goes out. I meant that the air is moving around and it finds a place to go whether it be under another piston or out the vent. We both know it won't go right under the other piston. The crank creates this effect, too(windage).

It was just meant as a simple explanation instead of saying the main cause and then having lots of people come in here and say "Nothing will get in the crankcase from the cylinders unless something is wrong."

 

[Calan]

Hey Sam... what do you guys run? Two AN fittings to a vented catch can, bypassing the vac side of the PCV system?

For drilled and welded AN fittings, are the VC baffles still in tact and unmodified?

 

[1992awdlaser]

Hey Sam... what do you guys run? Two AN fittings to a vented catch can, bypassing the vac side of the PCV system?

For drilled and welded AN fittings, are the VC baffles still in tact and unmodified?

Most people I have seen with AN setups leave the baffles in in order to limit how much oil gets out.

 

[Sam@RRE]

This is seriously over-engineering a catch can. Theoretically it would be nice to have vacuum suck out the positive pressure but really in reality, a piston moving upwards is able to compress the volume of the cylinder + boost, moving a little bit of positive pressure out of the crank case is cake for it. We just run both the PCV and vent to a simple catch can. Done. Doubt there's any benefit of one way or the other way, big thing is that you aren't coating your IC pipes with oil, because oil is an insulator and guys running MAFT setups (ie me) it will screw up your readings.