catch can pulling vacuum from turbo inlet?

**SS Ball3r** · 11-23-2019, 08:12 AM

Hey everyone,
I am trying to decide how to set up my catch can on my m52 turbo. I would love to draw some vacuum like the air/oil seperator from the factory worked. Connecting to the manifold would obviously create positive pressure into the crank case when under boost, so it would seem that either using a check valve of some sort, or probably better connecting to the turbo inlet. What I am curious about is if its possible to draw too much vacuum this way and create too much vacuum in the crank case? I'm thinking probably not, but I thought I would check for feedback before I do this and hurt something.

**mitchlevy7** · 11-23-2019, 11:10 AM

This is how I have it. -10 out the valve cover to catch can to -10 to the turbo inlet. No issues so far. The only reason you may run into issues is if your air filter is clogged (creating more vacuum in the turbo inlet) or if your turbo inlet is small and restrictive. I am running a super short 4" inlet into the turbo with a pretty big filter.

I had a buddy who was having issues with his dipstick popping out from too much pressure on his turbo s50 and routing it like this solved his issue as well. I believe the crankcase was vented to atmosphere and that is what was causing issues.

Yes, you can pull too much vacuum from your crankcase and it can cause oiling issues as well as destroy the crank seals, however i haven't encountered it with this method. the only time I encountered it is when the intake manifold was pulling vacuum out of the crankcase with a -10 line and it would squeak at idle, however, switching to a smaller line fixed the issue. Alot of the guys that run vacuum pumps for crankcase pressure have a regulator on them so they don't pull too much vacuum, for this reason.

This actually how alot of factory turbo cars I work with run it. In boost, the PCV valve which is connected to the intake manifold closes (kinda like the check valve you were talking about) and the crankcase is vented through the valve cover and goes back into the intake preturbo. The vacuum in the intake tube helps to pull the gasses out of the crankcase.

**SS Ball3r** · 11-23-2019, 06:45 PM

Thanks for the feedback. I have a pretty big 4” filter as is. I wonder if going with a smaller line from the inlet to the catch can as a pseudo restrictor would be a good idea? the car is meant to be a track car, so it’s definitely going to see lots of time in boost.

**pbonsalb** · 11-23-2019, 07:34 PM

Most of us don’t use vacuum because it pulls oil into the intake. Some vent to atmosphere, some use an exhaust scavenge, some use electric vacuum pumps, and a few used belt driven pumps.

**SS Ball3r** · 11-25-2019, 11:55 AM

Originally Posted by pbonsalb

Most of us don’t use vacuum because it pulls oil into the intake. Some vent to atmosphere, some use an exhaust scavenge, some use electric vacuum pumps, and a few used belt driven pumps.

I would think that with a proper catch can setup in the middle you shouldn't be pulling any oil into the turbo inlet?

**Hova** · 11-25-2019, 01:35 PM

Originally Posted by SS Ball3r

I would think that with a proper catch can setup in the middle you shouldn't be pulling any oil into the turbo inlet?

It's never a perfect oil catch, and depending on engine there is different amounts of blowby.

I vent it to atmosphere, though into an exhaust scavenge works really well.

**NOTORIOUS VR** · 11-25-2019, 02:03 PM

With a good can, properly located/designed you shouldn't be pulling any significant oil into the intake at all.

**pbonsalb** · 11-25-2019, 02:19 PM

Theoretically.

**jakermac** · 11-25-2019, 08:02 PM

Originally Posted by NOTORIOUS VR

With a good can, properly located/designed you shouldn't be pulling any significant oil into the intake at all.

Agreed. And I cannot stand the smell of oil vapor that inevitably make it's way into the cabin when daily driving an atmosphere vented system. I went from a pretty consistently oily intake tube, TB and intake manifold to ZERO with the implementation of my catch can. But I had it vented to atmosphere. Then I connected it to the intake tube from the top of the catch can with a -12 line. Suddenly the smells were gone, and I STILL had NO oil in the intake system. Now mind you this was an N/A motor, but I was making 270/240 at the wheels and spinning it to 7,800 rpm. I plan to implement the exact same catch can in my turbo build, with the exception of attaching the -12 line from the top of the catch can to the inlet tubing ahead of the turbo.

**NOTORIOUS VR** · 11-25-2019, 08:56 PM

Originally Posted by jakermac

Agreed. And I cannot stand the smell of oil vapor that inevitably make it's way into the cabin when daily driving an atmosphere vented system. I went from a pretty consistently oily intake tube, TB and intake manifold to ZERO with the implementation of my catch can. But I had it vented to atmosphere. Then I connected it to the intake tube from the top of the catch can with a -12 line. Suddenly the smells were gone, and I STILL had NO oil in the intake system. Now mind you this was an N/A motor, but I was making 270/240 at the wheels and spinning it to 7,800 rpm. I plan to implement the exact same catch can in my turbo build, with the exception of attaching the -12 line from the top of the catch can to the inlet tubing ahead of the turbo.

Same thing applies to boosted motors to be honest. No reason not to recirculate if you do it right. It's not always easy but done right it works as intended and you don't smell like an oil refinery

**3literheater** · 11-29-2019, 11:22 PM

How would you do this on a top mount setup?

**Robocop** · 11-30-2019, 06:27 PM

to the ppl who do it right have u taken off any pipes and is it oil free?
does it contribute to pinging since it sucks in not so fresh air?

**pbonsalb** · 11-30-2019, 10:53 PM

The first question is a good one to ask. Pay the most attention to the guys who have been running 20+ psi with their recirculating catch cans. With your perfect, well plumbed fancy recirculating catch can, what is your plan for running in boost when your check valve prevents flow to the can? Your crankcase pressure will go up and push into the compressor and send oily air through your IC pipes, IC, HFM and intake manifold.

The only really good solution is venting to atmosphere, running a dry sump or a vacuum pump. No electric pumps work perfectly but some might help. A belt driven pump is best.

**Z-Thrizzle** · 12-02-2019, 09:53 AM

Originally Posted by pbonsalb

The first question is a good one to ask. Pay the most attention to the guys who have been running 20+ psi with their recirculating catch cans. With your perfect, well plumbed fancy recirculating catch can, what is your plan for running in boost when your check valve prevents flow to the can? Your crankcase pressure will go up and push into the compressor and send oily air through your IC pipes, IC, HFM and intake manifold.

The only really good solution is venting to atmosphere, running a dry sump or a vacuum pump. No electric pumps work perfectly but some might help. A belt driven pump is best.

I tried searching but haven't found much info on running a belt driven pump. Have you come across anybody running such setup on an M50, M52 or S52?

**NOTORIOUS VR** · 12-02-2019, 11:58 AM

Originally Posted by pbonsalb

The first question is a good one to ask. Pay the most attention to the guys who have been running 20+ psi with their recirculating catch cans. With your perfect, well plumbed fancy recirculating catch can, what is your plan for running in boost when your check valve prevents flow to the can? Your crankcase pressure will go up and push into the compressor and send oily air through your IC pipes, IC, HFM and intake manifold.

The only really good solution is venting to atmosphere, running a dry sump or a vacuum pump. No electric pumps work perfectly but some might help. A belt driven pump is best.

I don't follow, why do you expect the system to fail? There are so many platforms that run recirculated PCV systems at high power levels. There is nothing special about BMW's that doesn't allow it to be done correctly.

**pbonsalb** · 12-02-2019, 12:12 PM

Yes a couple of people have done it here and posted details. Hard to fit with all accessories.

**pbonsalb** · 12-02-2019, 12:17 PM

Originally Posted by NOTORIOUS VR

I don't follow, why do you expect the system to fail? There are so many platforms that run recirculated PCV systems at high power levels. There is nothing special about BMW's that doesn't allow it to be done correctly.

It’s great you are able to manage 10 second long pulls with a big turbo running at 20+ psi that triples stock power. Where is the crankcase pressure going while the pvc is closed?

**NOTORIOUS VR** · 12-02-2019, 01:19 PM

Originally Posted by pbonsalb

It’s great you are able to manage 10 second long pulls with a big turbo running at 20+ psi that triples stock power. Where is the crankcase pressure going while the pvc is closed?

I really don't understand what you are asking. How much power a car makes makes exactly ZERO difference on PCV system design except for the size of the system to handle the extra CC flow. But the system is designed in exactly the same way every single time.

Crank case pressure when the PCV valve is closed, CCV is then routed to the intake system BEFORE the throttle body - and on a turbo car that is somewhere between the air filter and the turbo's inlet.

**et89** · 12-02-2019, 04:25 PM

Originally Posted by NOTORIOUS VR

I really don't understand what you are asking. How much power a car makes makes exactly ZERO difference on PCV system design except for the size of the system to handle the extra CC flow. But the system is designed in exactly the same way every single time.

Crank case pressure when the PCV valve is closed, CCV is then routed to the intake system BEFORE the throttle body - and on a turbo car that is somewhere between the air filter and the turbo's inlet.

I am not sure if I am following Phonsalb correctly either, but is either one of you talking about a system that uses check valves?
What do you mean by "doing it right" ?

I have mine the simple way, from crankcase too mishimoto catch can to atmosphere.
it works ok.

**NOTORIOUS VR** · 12-02-2019, 05:45 PM

Originally Posted by et89

I am not sure if I am following Phonsalb correctly either, but is either one of you talking about a system that uses check valves?
What do you mean by "doing it right" ?

This thread is about pulling vac/recirculating PCV systems - not vent to atm.

I have mine the simple way, from crankcase too mishimoto catch can to atmosphere.
it works ok.

See above.

**pbonsalb** · 12-02-2019, 05:48 PM

You want vacuum assist but can’t have it under boost, which means you block the vacuum/boost with a check valve. The oily crankcase vapor is coating your intake manifold. There is a reason why none of the long time high boosters are running recirculating catch cans with vacuum assist. Even a great filter/baffle system will pull oil through.

**Robocop** · 12-03-2019, 12:06 AM

my ignorant point of view on putting it in front of the turbo is that it's basically
eating it's own shit possibly make it ping where vented to atmo wouldn't. ?

also an oily layer all up in my compressor housing and nasty gunk coating the cooler.

obviously you need a big badass catch can to keep it minimal
i haven't looked into it, i bet there is some can out there that keeps it just to vapor. maybe not.

**et89** · 12-03-2019, 02:16 AM

Originally Posted by NOTORIOUS VR

This thread is about pulling vac/recirculating PCV systems - not vent to atm.

See above.

I know it is about recirculating, i should refrase my question:

Is "doing it right" the same as what I have, but routing it back into the turbo inlet? i have done that before with an old worthless catch can and that oiled my intercooling piping nicely.
I understand the concept of recirculation. But my question is what your concept is for "doing it right"?

Originally Posted by pbonsalb

You want vacuum assist but can’t have it under boost, which means you block the vacuum/boost with a check valve. The oily crankcase vapor is coating your intake manifold. There is a reason why none of the long time high boosters are running recirculating catch cans with vacuum assist. Even a great filter/baffle system will pull oil through.

I understand why you would want a check valve for vacuum assist to the intake manifold. But where do the phumes go when under boost? because this way you basicly block your crankcase vent when under boost and build up pressure.

**pbonsalb** · 12-03-2019, 08:08 AM

These are good questions and there has been much discussion here over the years. Search for “crankcase vent.” A few have done systems with electric assist from a SAP using a check valve and switch that blocks boost and turns the pump on. That looked promising to me. I have a full accessory car and can’t fit a belt driven pump even if I wanted to spend $400-$1000 on one so a pump for me would have to be electric and none are really rated for this use. I also ran an exhaust scavenge for a while. I vent to atmosphere with a burger catch can and breather. I’d be interested in better systems, but have followed this forum for the last 15 years and have a pretty good idea about what people have proven to work on these cars with big turbos creating a lot of pressure in a small block during long pulls under boost.

**NOTORIOUS VR** · 12-03-2019, 09:16 AM

Originally Posted by pbonsalb

You want vacuum assist but can’t have it under boost, which means you block the vacuum/boost with a check valve. The oily crankcase vapor is coating your intake manifold. There is a reason why none of the long time high boosters are running recirculating catch cans with vacuum assist. Even a great filter/baffle system will pull oil through.

You DO have vacuum under boost - there are two channels at play in a boosted PCV system. One during high vac. situations and one during boost/low vac situations.

You are simply wrong about "even a great filter/baffle system will pull oil through" why would a proper system coat your intake system in oil - if it DOES, you have a problem with blow-by that no system can fix or you have an indaiquate PCV system with a oil separator that obviously isn't working correctly.

I really don't understand why you seem to think that you cannot have a high performance recirculated PCV system. OEM's do it all the time - the aftermarket has done it as well.