Guys with blow through setup and catch cans

[thebird_19]

I've been reading the stupid pcv thread and I've searched, but can't really find anything about using catch cans with maft and blow through. Do you guys just run the catch cans like you would normally and if so does this pose a problem with unmetered air being pulled into the vc from the intake(before turbo thus before maf?) Just curious how, if any of you are running this setup. Thanks,
David.

 

[dsmfa9nutter]

What's the problem? The catchcan goes to the vc and the hole in the intake is plugged.

 

[thebird_19]

No, the vc would be pulling air from the intake which is before the maf in blow through mode which would be unmetered. I'm just wondering if anybody running a blow through setup has problems with idle or tuning due to this, or if it will be okay to just hook it up as normal.

 

[Mr Peepers]

Run a catchcan between the VC and intake tube.

Otherwise, like you said, unmetered air will get sucked in through the VC breather and into the intake manifold through the PVC valve under vacuum.

EDIT: Still unmetered air since it's pre-MAF... I'm still thinking draw through for some reason

 

[snowborder714]

I run blow thru with 2 catch cans. One inline between my intake and the valve cover. The other inline between the PCV valve and the intake manifold.

I have not noticed any problems during idle. I just started tuning tonight but it didn't seem to pose a problem either. I haven't done WOT tuning yet, but I don't see that being a problem either.

 

[92awddsm]

I run blow thru with 2 catch cans. One inline between my intake and the valve cover. The other inline between the PCV valve and the intake manifold.

I have not noticed any problems during idle. I just started tuning tonight but it didn't seem to pose a problem either. I haven't done WOT tuning yet, but I don't see that being a problem either.

Even hooked back to the intake tube, with a blow thru, it is still unmetered air. Only way to reintroduce the air pulled through the crankcase without it being unmetered is to have it reinter the system aft the mas. Thats not as easy as said with a blow thru system.

Most people just richen the idle with a blow thru system to combat the lean condition cause by still using a pcv. Wot is not affected with a properly functioning pcv valve.

 

[thebird_19]

Cool guys, thanks for the help.

 

[Black_Bullet]

Any time i hear anything about catch cans or pvc related issues i get a headache.
I cant even properly set up mines or get discouraged by long confusing threads on trying to read how to properly set it up with dual catch cans and all this check valve stuff.(sigh)

I will say just slightly richen your tune for the unmetered air, it shouldnt be that significant.

 

[hereitcomes]

Learning that process though will save you time and a large headache later on when you finally decide to run two catch cans. : )

 

[Black_Bullet]

Learning that process though will save you time and a large headache later on when you finally decide to run two catch cans. : )

Yea i know one day... I just always tend to put it on the back burner.
At least i run good oil and change it every 2-3k.

 

[JeffGST]

Simplicity is key. DSM's always seem to have problems, and the way to diagnose these problems are to simplify things so that the process of elimination is easier.

The simplest way to run a catch can setup with a GMAF is to remove all the catch can lines from the IC pipes. The catch can lines should run to the valve cover and T into nothing else. Introducing the valve cover lines to the IC pipes is only asking for metering trouble. I hate oil in my pipes and SMIM.

Simple. No effect on metering.

EDIT : There is no effect on metering, unless you have massive blow-by through the rings. Large amount of Blow-by will cause metering problems since the metered air through the GMAF went through the motor without by combusted. Instead it went right out of the oil catch can and cause a rich condition.

 

[1992awdlaser]

Couldn't you just put one line to the side of the valve cover and the other to where the pcv is. This of course would eliminate the pcv valve and you would have to block it off at the intake manifold.

 

[Dsm2nr89]

I had a 91 tsi awd last year and i had a gm maf with maf-t setup and i never had any of these problems. Matter of fact i just put on a breather filter on my vc and ran the car open turbo and i never had an idle issue.

 

[Notstock]

Don't want to dig up an old thread but it's better than starting a new one... I'm going to be changing the draw through to a blow through here shortly and have similar questions about this. Can't you just do this... VC -> sealed catch can -> weld a nipple onto the ic pipe after the maf and before the throttle body? Then run another sealed catch can between the pcv and the intake mani? I'm not sure why everyone is having such a hard time with this...

 

[talonDSMerr]

I'm wondering the same thing, and that would make sense. But welding the nipple after the gm maf and before the throttle body brings positive pressure/boost into the equation. I'm not sure if that would affect anything, but in stock configuration, the line from the valve cover to the intake never saw boost. So I'm wondering if that changes anything.

 

[Weapon-X]

You can probably use a check valve on that line.

Check US Plastics................

 

[90laserRSfwd]

I had a 91 tsi awd last year and i had a gm maf with maf-t setup and i never had any of these problems. Matter of fact i just put on a breather filter on my vc and ran the car open turbo and i never had an idle issue.

+2

 

[Steve93Talon]

Don't want to dig up an old thread but it's better than starting a new one... I'm going to be changing the draw through to a blow through here shortly and have similar questions about this. Can't you just do this... VC -> sealed catch can -> weld a nipple onto the ic pipe after the maf and before the throttle body? Then run another sealed catch can between the pcv and the intake mani? I'm not sure why everyone is having such a hard time with this...

I'm wondering the same thing, and that would make sense. But welding the nipple after the gm maf and before the throttle body brings positive pressure/boost into the equation. I'm not sure if that would affect anything, but in stock configuration, the line from the valve cover to the intake never saw boost. So I'm wondering if that changes anything.

Do NOT do that. The point of the valve cover breather is to VENT crankcase pressure. You'd be introducing a pressurized source to your crankcase and not only would you not be venting pressure, you'd be pushing more air into the engine. This would cause bad things to happen like oil pushing past your turbo seals and smoking like mad.

I attached a diagram of how to properly do it. Ideally you want catchcans that are either baffled or filled with something like steel wool to separate the oil as it passes through. The 2nd catchcan doesn't necessarily have to be routed back into the turbo inlet pipe, you can just have a breather filter on it. Ideally, if the 2nd can is recirculated to the inlet pipe, the suction from the turbo while in boost acts as a vacuum pump, which helps extract the crank pressure better, helping prevent blow-by and actually pulling the rings against the cylinder walls to help seal them, theoretically gaining power.

 

[talonDSMerr]

But Steve, venting the valve cover to the intake pipe means you're venting metered air out of the system when running a blow through setup, because you would now be venting before the maf. As you said, though, venting it in the intercooler piping after the gm maf would introduce a pressurized source but wouldn't placing a check valve in that line, as Weapon-X stated, work?

 

[Steve93Talon]

You'd only be letting metered air out if you have massive blow-by, otherwise it's too negligible to worry about, just compensate for it in your airflow correction if necessary. Putting a checkvalve would stop boost pressure from entering the crankcase, but it still wouldn't give you any escape for the crankcase pressure. You'd essentially be corking up your engine, which would not be good. With a MAF before the turbo, you can route the vented pressure back into the turbo inlet pipe, which effectively eliminates any metered air escaping.

You could always put can #2 on a valve with a pressure switch so that you'd only be venting through it at WOT, otherwise it'd solely be returning to the intake manifold through the PCV. I've never tried this, no clue if the PCV alone would be able to sufficiently vent the crank pressure at idle/cruise.