Do not use Bronze Filter on Catch Cans or AOS!?
 

Finally found a video on the effects of catch can restriction on crankcase pressure. In the video he is using a DPS from the oil cap with arduino reading the DPS during idle on his Diesel engine. Basically the 50micron bronze filter we see in catch cans can increase crankcase pressure by up to 4x since its too restrictive. Better to stick with big catch cans, big fittings like cusco without any filtering.

In his setup he claims that pressure is the highest during idle since turbo boost will start generating vacuum in the crankcase (not sure if its correct but I'm not familiar with turbo Diesel setups maybe the PCV connection is before the snail). It would be great to duplicate this on our platform under boost.

But to extrapolate his finding to gasoline engines where blow by will increase with RPM/boost we'll see more then the mbar increases he's seeing. jump to 17:39 in the video for the results but to summarize

all tested during idle
Baseline no Catch can: 1.55mbar
Mann-hummel Provent (paper or steel filter): 1.54-1.58mbar
Mishimoto with bronze filter: 6.20mbar
Mishimoto with no filter: 2.8mbar
Universal oil catch can no filter: 2.1mbar
Universal oil catch can steel scour: 2.4mbar

Thoughts?

https://www.youtube.com/watch?v=fiAs52P7Qwg

PCV systems exist for more than emissions, they help the engine by keeping blowby gasses from contaminating the oil, and they increase power by creating a vacuum on the bottom of the piston. The effects of this are shockingly large for what seems like such a small change.

Vent to atmosphere catch cans that completely disable the PCV system are snake oil at best, and slowly destroying your engine at worst. With the oil contamination they allow you really should be decreasing your oil change interval if you're running one. An oil analysis will tell you how often, anything else is just a wild ass guess.

Any street driven car, regardless of how much boost is can make, spends the majority of its running life with a partial vacuum in the intake manifold. If it takes 20hp to move your car down the road at highway speeds when its NA it doesn't suddenly take way more once you strap a turbo to it. Ok, the back pressure from the turbine might bring it up to 21hp, fine. The point is the engine still spends the majority of its life in a cruising state with a partial vacuum in the intake. There is absolutely no reason to not use a proper PCV system in a street car, especially these cars with D4S, you have the vacuum source readily available.

For race cars, I've seen people go to some pretty big extremes to get vacuum in their crankcase, vacuum pumps is where a lot ended up, but I saw a few drag racers using a port in the merge collector of their headers to pull a vacuum on their crankcase.

If the crankcase is always in positive pressure because of blowby gases then why does the crankcase need vacuum to clear out the gases? There would be slightly higher crankcase pressures or resistance without the pull of the vacuum compared to atmospheric pressure, but it still should vent. I guess the thing to do is to test crankcase pressure when connected to vacuum versus open to atmosphere. Take the hose off the PCV, and air is constantly blowing out of it, so is vacuum really necessary, and wouldn’t venting it in any fashion keep the oil cleaner?

Most synthetic oil is good for more miles than I use. The AMSOIL says 1 year or 25k miles. I never wait that long. I would rather run open and minimize any oil and gases getting back into the intake.

I'm sure this isn't news, but the PCV is a pollution control device. It runs blowby gases and oil vapor through the combustion cycle.

I vaguely recall my drag racing friends from the 60s and 70s going to considerable lengths to scavenge the crankcase. They did it primarily to reduce windage and pumping losses from the crankshaft and rods whipping around and the pistons thrashing up and down. One of the solutions I thought was pretty cool was they would tap into one of the header collectors at an oblique angle and use the negative pressure generated by the exhaust gases flying past to evacuate the crankcase. Simple, virtually free, and very effective.

I'm pretty sure today's generation still uses the same tech.

I know that part. The controversy is more about the debate between open and closed loop systems as it relates to performance and reliability.

He mentioned the same thing. I think there is a difference between a drag car and a street car. The power difference might be more significant on a high horsepower vehicle, especially a V8, and especially on a vehicle trying to maximize power. Also, the drag car sees very little vacuum by comparison.

The alternative to an open system is a closed system with a PCV valve, which will have moments where it isn’t allowing the crank to vent, so I guess the question is which is best/worst: a system with vacuum pulling air and pressure spikes during boost, or a vented system with no vacuum, but no spikes either? I don’t know.

I should have the posts more closely. Sorry. You know much more about running boosted engines than I, but, for environmental reasons I would scavenge the crankcase rather than vent to atmosphere. If I read Calum correctly he contends the performance impact is significant . I have not seen any definitive research on that subject, but as I said, I'd run closed loop, if only for pollution mitigation.

The catch can will catch the oil and gas, and the filter will screen the air. It probably won’t be perfect, but it should be good enough. Compared to other forms of omissions, this is very little.

I would rather not see pressures peak under power. If anything will rob power, wouldn’t that? I know a large V8 with 1000hp might see a 30hp change in peak horsepower, but I doubt a I4 with 400hp will see much difference in power from having less windage/air molecules in the crank. I’m less concerned about 5hp.

Pneumatic filters are rated by how small of a particle they will remove, and flow rate @100PSI . You can get different filters in the same material with more flow rate. Just because Mishimoto puts a bronze filter on a catch can and it doesn't flow well, doesn't mean all bronze filters are bad.

Understood. IIRC the guy in the video measured pressures at idle. I suspect that under power CC pressures would rise. Further, I suspect that under boost and power they would rise even more. Throwing restrictions on the downstream side should exacerbate that. Depending on a lot of variables I don't have the ability guess at, I think I'd be a little concerned about seal integrity. I understand that street cars spend little time under boost so I may be counting angels dancing on a pin. That said, although the emissions of an individual car are very small - I still want to minimize them where possible.

Given that you don't have negative (below ambient) pressure in the intake under boost and attaching the CC vent line on the suction side of the compressor is a non-starter - it's a tough one. I don't have the ability to test it, but I'd be interested in seeing someone (not you necessarily) try something like the exhaust evacuation approach back to back with atmospheric venting. On the upside, exhaust evacuation should kill the emissions bird along with CC pressurization.

I wonder what the folks running IMSA, WEC or F1 cars do with this? Anybody know?

I guess the other thing is that the PCV system is sucking unmetered air into the intake manifold, which seems bad, but maybe the stock tune compensates for this or maybe the physics works out somehow.

I agree that proper catch can sizing and baffling is important. I just don’t know that a closed system is best or necessary.

Good luck with it.

The stock PCV system pulls air from after the MAF so it is both filtered and metered.

It was metered and filtered. Then it went through the cylinder. It is essentially exhaust gases that get fed back into the intake manifold. The intake manifold has a hole. Disconnect the hose and unmetered air is getting sucked into the manifold. Connect the hole to exhaust gases, and you have the EGR system. Connect it to blow by gasses from the crankcase and then you have the PCV system. This air is compensated (predicted) by the computer, but not measured. Read the EGR article. Sounds a lot like the PCV system.

https://en.m.wikipedia.org/wiki/Exha..._recirculation

True, it should be a small volume compared to what the engine ingests tho. The PCV valve isn't either open or closed. It is closed at low vacuum, open at mid vacuum and partially closed at high vacuum. On top of that the PCV hose is only 3/8" or 1/2" in diameter.