mrdrpep

I drew up a very simple diagram for a breather/crankcase oil catch can and scavenge catch. Will this work properly? I have heard of the possibility of using a 'scavenge' system on the exhaust downpipe from turbo (after the o2 sensor). Will that create enough vacuum (if placed at the proper angle) under boost? The idea is to use the normal engine vacuum to pull crankcase vapors back into the engine (like oem), but while under boost, a series of checkvalves prevents boost from going backwards. The vacuum created from the exhaust flow (under boost) will continue to pull the vapors down into the exhaust and burn them up. I believe a scavenge on the turbo inlet would work but would make an oily mess in the intercooler piping, etc.. Why not dump them right back into the exhaust? Also, would it be better to just vent the valve cover or have it T into the catch can lines as I have drawn in the diagram? Is it a problem to have vacuum on the breather on the valve cover or should that simply be routed to the air inlet pipe before turbo?

SIR-G Amp

With that system you have I would probably run a filtered breather on the valve cover and not a T. That way, fresh air can enter the engine while the intake manifold pulls vacuum on the crankcase. Keep in mind the size of hose you use as this is technically a "vacuum leak".

-Amp

mrdrpep

Ok... makes sense. I guess I always assumed that the valve cover vent was a vent, not intake. So the vacuum that would be on the crankcase ventilation would be pulling through and coming in the valve cover breather. Yes, I just had that aha moment.

This is currently how I have it but without the catch can.

TheShodan

iTrader: (14)

-Other side of check valve needs to go to the valve cover vent breather port, not "T"-d off with a line going to the catch can.
-Why 2 check valves? the one going to the intake manifold will be fine enough. DO NOT USE OEM CHECK VALVE, it does not 100% seal like a brake booster check valve does from a turbo factory car. It's supposed to be a one way check valve.
-No need to "scavange" from the downpipe either. It won't create a vacuum down like you think.

2kdrift

exhaust assisted vacuum will not work as well as you may be thinking, Im also not a big fan of running vacuum to my IM..... tried it and it pulled too much oil for my liking, and it was messing with my ability to lower my idle.

Simple 2 port breather off the back of my VC works just fine your diagram seems overkill

boosted94gsr

What's the point of running a complicated recirculating system? For emissions? Why not just keep it simple and run 2 ports off the valve cover or back of the block to a vented catch can. Simple and effective.

mrdrpep

Thanks for your input, and sorry for over thinking it. Makes sense about the valvecover T. I would do away with that idea and just use filter/breather (which is what I'm currently using).

It's not really a goal for emissions or for making a complicated system. It's not an accident that cars came factory with vacuum on the crankcase to pull vapors out. There is positive pressure in the crankcase so it may be enough to run it as you say, but using vacuum is how it's been done. I'm not sure this is totally for emissions. My goal would be to keep it oem-like but to catch more vapors in the can before returning to intake. When in boost it pressurizes the whole intake manifold and blocks the vapors from going their normal route (through the normal PCV system) so this system would allow them to pull another direction. Most people who do this correctly will run a scavenge on the turbo inlet pipe and using two checkvalves as I drew in the diagram. The two checkvalves in this system would be to prevent vacuum from pulling back through that line (under normal engine/cruising vacuum), otherwise it would be trying to pull vac on the "scavenge" line. Then under boost, the other one would close (near the intake) but still allow vapors to "scavenge" and burn up in exhaust via the other line. I've found a few examples of people doing this and I don't believe it would take much to pull the vapors out. Since the crankcase has positive pressure anyway, it may be enough. I'd like to see a test done of a proper downpipe scavenge system to see how much it's able to pull. The turbo is putting out an incredible amount of exhaust and high velocity under boost, so there's going to be a pulling effect if set up properly. That's why I wanted to post this here because I haven't seen many people doing it this way...

example of exhaust scavenge:

2kdrift

there are advantages to using a vacuum to pull vapors out, particalry when driving is traffic and not seeing much boost at idle etc. however I dont find the need to do so and dont like oil going into my IM and cylinders. when running scavenge through the intake intet pipe there is no need for a checkvalve, if i had to choose a scavenge method I would go that route but still dont want oil being sucked into my turbo either.

I have been through this same line of thinking you are currently in when I setup my turbo system, tried the IM vacuum method but did not like it

here is the info I saved which I found to be best solution for vacuum catch can thanks to shodan

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Then by all means, please have your experience with it. I've had those setup on some other cars I've had around and it was awful.
And I don't do the vented valve cover setups either (they aren't necessary from my experience).
I keep a pretty simple drain back system using a S80 Volvo boost check valve to stop all the vapors and mess at startup.
I can't even take credit for the idea, it was my friend and engine builder who perfected it with a B&R Catch can system.

Below is the PCV "black box" canister adapter fitting that is used as the drain back.
This is the S80 Check valve running from the Valve cover fitting routing to the intake manifold

The 1st is the drain-back, the other two are the crankcase breathers themselves.

Notice the color orientation of the S80 check valve. It's a one-way valve. It routes down and through the runners, just like the original PCV valve.

Top two fittings go to the back of the block where crank case is highest. Valve cover w/ check valve goes to Intake manifold front. Crankcase issues are rarely at the valve cover baffles contrary to popular opinion.

Bottom port drains back to the block as you stated.

Not one puff of smoke, not one saturated canister filter.

mrdrpep

Sorry to bump this thread back up but I thought I would post my solution. The short answer is this: I am basically keeping the crankcase ventilation stock with some nifty exceptions (as per that diagram above). Under normal driving conditions, I am still sucking crankcase gases back into the engine except they are going through a catchcan first. So it's cleaner than OEM. Then, under boost, all the crankcase gases are immediately routed into the exhaust. This works by using a PCV (brake booster pcv mind you, thanks Shodan for that info) completely closes, preventing boost from entering the crankcase/flowing backwards.

There are two PCV's and they alternate roles to allow the gases to go either way (towards the intake under vac, and towards the exhaust under boost). This idea works great because your keeping suction on the line at all times so those gases can get out faster. It's important to have no backpressure on exhaust so as to allow the scavenge to suck out, rather than have positive pressure from a lousy exhaust. A good scavenge setup under boost can pull between 5-8" of vac which is enough considering there is already a little positive pressure from the crankcase anyway.

(edit: also, I'm just using a breather filter on valve cover. Although it wouldn't be a bad idea to have a separate catchcan with a breather on top just for that).

pics..
Catchcan mounts on firewall. Line on left goes to intake manifold. Brake booster PCV allows vac, but closes under boost. Next line from left goes to crankcase. Gases are always being pulled from this line. The next line over is the scavenge to exhaust line. It has an upside down PCV that is CLOSED under vac, but opens under boost. It takes very little if any pressure to open this so it allows the bypass under boost to scavenge to exhaust.

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DIY Scavenge pipe. Note the angle of the end cut and the slits cut above to capture the massive amount of exhaust gases flowing through downpipe to pull out.

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This will be mounted with the slits facing the exhaust flow, at an angle, to pull out.

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scavenge is mounted AFTER o2 sensor! The o2 bung is on other side of pipe, upstream.

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Ignore my fluxcore welding job... scavenge on downpipe



I may try to get a vac gauge and see what type of vac it can pull under full boost.

mrdrpep

So I tested this out and it definitely works! At idle, there is slight positive pressure on scavenge (this is why you need an all steel check valve/pcv coming off scavenge pipe to prevent exhaust going that way when exhaust flow is idle/slow), but under boost you can hear it sucking in pretty hard. It actually wistles like a mini turbo. I discovered I needed to keep the stock pcv to limit the flow/vac going back thru catch can back into intake. It was too much of a vac leak.

This probably looks a bit overkill and unnecessary but the point is that there is now always suction on the crankcase gases, which is better than hoping they find their way out into a standalone catchcan.

wunfstgsr

Could this work on a Supercharged setup with the scavenge welded to the exhaust manifold?

Also confused on whats done with the oem black breather box and oem pcv valve? And where does the line for the catch can to crank case get attached too? the back of the block with a fitting replacing the oem breather box or to the pcv valve on the breather box?

mrdrpep

I believe it would work but you may want to go a little downstream on the exhaust. A supercharger is still blowing a lot of air through the engine so there's an increase in total amount of air going out of the exhaust. But again, you want a nice open exhaust with as little restriction as possible.

Currently, I have the stock PCV valve in with the original box attached to the back of the engine. Gases are still being sucked into intake manifold under vac (except I'm routing them thru catchcan first to clean them up some). Then under boost, the brake booster pcv closes (totally blocks all boost from creeping into the pcv system). While under boost, there is more than enough vacuum from scavenge to pull gases out.

wunfstgsr

So the catch can never really fills with oil with this setup and just routs back through the oem black box? thats the setup id prefer..

I was thinking to put the scavenge right after the header collecor twareds the end on the straight pipe that replaces my cat..

mrdrpep

No, the secondary catch can (that red one pictured above) still has oil vapors/gases being sucked through. Although, I need to modify mine to incorporate baffling or material to give more surface area for the vapors to cling to. It's important that this catchcan be airtight as it will be under engine vacuum. And yes, the stock one on the back of the block is still being used as it was intended. It all passes through that first. Here's the order of events:

1. Gases coming from back of block route through the black oil catch can and stock PCV valve system as they normally would.
2. However, from the stock PCV valve, I route through my secondary oil catch can mounted on firewall
3. ..then directly back to intake manifold (vacuum). This is the line that uses the brake booster PCV to allow vac/flow towards intake, but stops boost from reversing.
4. Then, for the alternate scavenge route, you tee off either line by the secondary catchcan. This line goes to the scavenge. It's important to have an all steel PCV/checkvalve on the scavenge pipe itself. I'm using moroso 97800 as it threads on the pipe. This not only stops positive pressure from exhaust at idle, but prevents vacuum from engine.

Pros:
-It looks complicated, but it's actually so simple.
-You don't have to touch the stock oil catch on back of block or climb in the worst imaginable position to get to it.
-Keeps vacuum/flow on crankcase gases like oem but is cleaner because they route through catchcan first.
-the scavenge provides enough suction and flow to get rid of those nasty vapors under boost and high rpm when it's needed most
-there's always suction with this system

Cons:
-Relying on more checkvalves. There are 3 total. If the steel scavenge valve were to fail, the car would run like crap. I'm just going to keep an extra checkvalve in the car if one fails. Also, if I were on a trip or something and had a problem, all I would do is pull one line off catchcan, and route to intake manifold like stock.
-requires cutting hole in exhaust and welding in a properly placed scavenge. If you get this wrong or have to much exhaust restriction, the scavenge would do absolutely nothing as positive pressure would keep the checkvalve closed.