What Do You Think Of This PCV Elimination Theory

[GNVYUS 1]

I just read a thread where David Buschur ( GN owner also :biggrin: ) ditched the factory PCV on his Evo and ran a catch can setup to the inlet pipe. He gained torque on the dyno with no other mod other than a driveshaft ( loss of rotating mass could have caused gain ).

Ditch PCV and run an open fitting in place to a catch can, catch can goes to inlet pipe ( no breather on catch can ). Use the turbo as a suction while under boost to suck out fumes.

By doing this you eliminate the possibility of the PCV opening while under boost and causing crankcase pressure which loses power and causes the breathers to smoke.

You also gain the suction of the turbo while under boost to help suck out crankcase pressure ( cheap pump ).

While under normal driving conditions you are still sucking out fumes from the crankcase like the PCV, it's only going to the inlet pipe instead of directly to the vacuum block. And since the catch can is there only fumes will get into the inlet pipe, not actual oil droplets etc.

I've suggested something similar before in these types of threads but it was based off of the breathers going to the catch can. I think his idea is even better by going to the PCV hole in the intake and sucking it 100% of the time right from the source.

Watcha think?

I think I'll try it but would like to see what others think and hash out any unforeseen issues. Eliminates any PCV issues and probably gains a touch of power with the best part being it's an evolution to Buicks initial idea.

 

[Chuck Leeper]

My $.02.
You are assuming that all the oil will precipitate into the catch can, and no oil will be pulled into the turbo inlet.
I think that is not 100% accurate, and that the high volume of air being drawn across the venturi of the inlet fitting, [especially @WFO], will pull oil mist out of the can.
Doing this will contaminate the intercooler, reducing it's efficiency, and eventually oiling down the T/B, and intake ports....The tried/proven system, using a pump, would be my choice.
Like I said, just my $.02.

 

[ckmm]

what kind of gains dose this give you ? what kind of pump do you need ? is it worth it ??

 

[bison]

I havent run a PCV in 10 years. Just plug it. Do not let turbo suck in hot oily fumes like the stock setup. It is not
needed in a high performance engine.

 

[GNVYUS 1]

CKMM, no pump needed, use the turbo's suction like the Buick engineers intended. He said torque went up quite a bit and the air difference on the dyno was at 68 degrees the first time and the new run with the catch can was at 100 in the shop so he felt like it was a real gain.

Chuck, if you've seen the catch cans where the PCV fittings are in the middle of the can and the inlet fitting being on the top I don't see how any oil could travel up and then through the tubing to the inlet pipe or even the ones that are at the top but side by side. Buschur commented how everything was clean after the runs also.

Bison, I'd consider ditching the PCV as I change oil every 1k miles anyways but then you lose the crankcase suction aspect this setup has. I think there is some power to be gained ( though probably not much ) and it'll definitely cure the puking breather issues. :biggrin:

 

[unix_punk]

A lot of people run this type of setup, maybe not TRs but works just as well. You can use a bunch of steel wool inside the catch can to assist in catching oil. The turbo really won't draw much from the can unless you have a restriction in your intake tract. Most of the air that is flown through there will be pushed through from the crackcase pressure, i.e. blow by. One thing is you will pull less air at idle than a PCV and you may need to adjust your IAT after you make the change because you no longer have that extra air getting in. I run mine in a similar fashion. Plugged the PCV on both ends and replaced the pass side VC breather with a nice -12AN 90degree bulhead fitting which goes to the catch can and then to the maf pipe.

 

[bison]

A lot of people run this type of setup, maybe not TRs but works just as well. You can use a bunch of steel wool inside the catch can to assist in catching oil. The turbo really won't draw much from the can unless you have a restriction in your intake tract. Most of the air that is flown through there will be pushed through from the crackcase pressure, i.e. blow by. One thing is you will pull less air at idle than a PCV and you may need to adjust your IAT after you make the change because you no longer have that extra air getting in. I run mine in a similar fashion. Plugged the PCV on both ends and replaced the pass side VC breather with a nice -12AN 90degree bulhead fitting which goes to the catch can and then to the maf pipe.

I wouldnt run that setup with a MAF'd car unless its nearly stock. There is a lot of vacuum there in cars making over 400 hp. If its got a stock MAF id forget it all together

 

[GNVYUS 1]

Good point on the PCV at idle, I'd bet you'd need to bump the throttle adjustment screw a touch to get more air in.

Initially I thought sucking both breathers was the best idea, but getting rid of the PCV and the possible problem of it opening while under boost is a nice plus. And sucking from the valley of the motor is ideal in this scenario, most Imports don't have that option and pull from the valve cover, we don't.

I'll see what Eric at TT thinks of the PCV IAC aspect.

 

[chasmat2316]

My $.02.
You are assuming that all the oil will precipitate into the catch can, and no oil will be pulled into the turbo inlet.
I think that is not 100% accurate, and that the high volume of air being drawn across the venturi of the inlet fitting, [especially @WFO], will pull oil mist out of the can.
Doing this will contaminate the intercooler, reducing it's efficiency, and eventually oiling down the T/B, and intake ports....The tried/proven system, using a pump, would be my choice.
Like I said, just my $.02.

Any pic's or a diagram of your tried & proven setup? thanx!

 

[chasmat2316]

I havent run a PCV in 10 years. Just plug it. Do not let turbo suck in hot oily fumes like the stock setup. It is not
needed in a high performance engine.

how do you vent the crankcase?

 

[JDEstill]

hmmm... a bone stock car has both the PCV and the hose from passenger side valve cover to turbo inlet. PCV works when manifold vacuum is high but not when boost pressure is high, it's an idle/cruise device only. At this time the turbo isn't spinning very fast, it's hardly pulling any suction, so no flow from the valve cover to the turbo. Matter of fact, I would suspect that the flow (if there is any) is reversed; if the manifold can pull any kind of vacuum on the crankcase via the PCV vavle, then I would expect there to be flow from the turbo inlet *to* the valve cover.

Once you get into the boost, the PCV closes (or at least it is supposed to), the turbo starts to make some suction (though for performance reasons we don't want it to - so we install high flow air filters and bigger MAFs and MAF pipes and such), and the turbo pulls crankcase vapors and blow-by to itself.

So, bone stock, cracnkcase vapors always end up getting burned - via the PCV at idle/cruise, and via the valve cover-to-turbo hose at boost.

Your idea, hose from crankcase direct to turbo inlet and no PCV, gets rid of the idle/cruise part of the equation. Well, not really, it can still get there, I'm just thinking that the turbo suction is so small at that time that it isn't going to pull anything meaningful. If you have a street car and are trying to keep a functioning PCV type system to help keep your oil clean, then this isn't the way to go. Now once you are in the boost, then I agree, the turbo will make some suction, pull crankcase vapors to it, and possibly give you some power by maintaining the crankcase below atmospheric pressure. So it's a WOT device only.

Now how much can it pull? I don't think it would be real effective, if the turbo suction is more than a couple of inches of vacuum then I would be looking for a problem. Again, we make mods to free up the intake system, because a free flowing intake gives us some power, and it does that by reducing the vacuum at the turbo inlet. All those things work against the turbo doing a good job of evacuating crankcase vapors. Not that it won't work, just that directionally it's moving the wrong way. And if the turbo is pulling, say, 3" of vacuum, then the best the crankcase will be is what, 1"? 2"? Still better than open breathers if it can pull any vacuum on the crankcase at all, but not that much better.

Me personally, if I have to make a choice, I would rather have a system that works properly at idle/cruise, since that is where the car spends 98% of it's time, and give up the part of the system that's effective under boost. I'm willing to give up a few hp to maintain a good crankcase vacuum at normal operating conditions, since that will keep the oil at its cleanest by evaporating any fuel, water, etc that might contaminate the oil. Not sure if it helps mileage or not, but it could, by reducing pumping losses. My setup is described in this thread:
looking for ideas on my Pcv system? - TurboBuick.Com
My setup works well at idle/cruise, but does nothing when under boost. Under boost my setup is no better than open breathers. But for me and my street car, that's a tradeoff I'm willing to make.

I guess a real vacuum pump is truly the best of both worlds, maintain a good crankcase vacuum under all conditions. Hey, it's only money

John

 

[bison]

how do you vent the crankcase?

It vents itself through 2 breathers in the valve covers. I just zip-tied a couple shop rags around the breathers. Its clean, easy to do, and keeps the mess out of the air entering the engine. No plumbing nightmare needed. I you are going to evacuate the crankcase it needs to be done independently of the air inlet tract. A vacuum pump has promising potential but is usually only used on race cars. They actually gain hp. They pull enough vacuum to contaminate the oil in a very short time with the amount of vacuum required to help hp. Any oily vapors that enter the air inlet will lower the detonation limit of the engine and coat the inlet tract with an oily film. As far as oil contamination goes if you have a high performance engine that has high cylinder pressures then you should be changing the oil frequently. Like weekly or even more if the engine is pushed hard. If you have to think about whether it should be changed or not change it.

 

[GNVYUS 1]

Here is why this should work IMO.

We are overlooking the fact that crankcase pressure is pushing pretty strongly up through the motor. This pushing will only be accentuating the sucking ability of the turbo in the inlet pipe during WOT. I wouldn't tie in the breathers with this theory as you don't want more dirty air in the motor, just let them help out and keep breathing the heads.

The fact that the PCV does creep open sometimes during WOT bursts gives you an example of how strong this force is in the crankcase as it's pushing open the flapper in the PCV even though it's getting boost pressure from above to keep it shut.

I bet during idle the pressure in the crankcase will be stronger than the inlets pressure in this hose. If the inlets pressure is higher it could push back into the crankcase but I really doubt this considering air is still moving through the comp wheel and this venturi effect will probably keep sucking the crankcases gases along with it.

I'd like to see if different catch cans effect these pressures, this is why I'm leaning towards a small catch can with a filter in it. The filter will help the dirty fumes and make sure no actual oil or residue gets into the inlet track, just hot air ( which is not nearly as hot as the compressor during boost ).

I'd not only do it for the slight power gain at WOT, but to help the seals etc in the motor. And I change oil a lot anyways so not a concern here if it did dirty it up more.

I think Norbs did something like this, I'd be curious what his setup was and his findings.

 

[BEATAV8]

What your talking about here is called a "closed crankcase ventillation" system. To work properly the crankcase must be closed (no breathers in the valve covers or anything) this way the turbo can pull a strong vacuum on the crankcase.

Basically this is just the stock factory breather setup minus the PCV.

It will have "oil carryover" from the crankcase to the turbo inlet, but low restriction in-line breathers for managing the oil carryover rate can be engineered into the system. Good breathers will have oil drain back systems in them, otherwise the filter will just load up and get soaked in a short period of time, and the oil will carry through anyways.

I work on systems like this for big diesels and I've considered it for my Buick, but I think Bison is probably right. Just eliminate the PCV and run 2 big 'ol honkin' low restriction open breathers on the valve covers. Simple is sometimes best. I'm going to set mine up like that with TA valve covers. This particular aspect of my engine has been ignored for too long and I'm tired of seeing the oil leaks that crop up only after running high boost.

PS.. the reason we do it on the big diesels if for emissions, not performance.

 

[unix_punk]

I agree with Steve the Pirate there will be no power gain, seal benefit or anything like that with open breathers. You need to draw at least 5in/hg to benefit you in any way and that's after the blow-by at WOT. The turbo inlet alone cannot do this unless you have a rediculous restriction. Unless you are willing to spend a lot of money on a mechanical vacuum pump (have to remove ac) or an electric system with check valves left and right then just do yourself a favor and run open breathers and put a check valve between the pcv valve and the vacuum block and be done. If you're gonna go mechanical I would look here Street / Strip Vacuum Pump Kits as they have pumps that can handle constant street use as they use the oil in the air they pull to lube the pump. With this type of pump you will need to eliminate all breathers and pcv.

 

[bison]

I agree with Steve the Pirate there will be no power gain, seal benefit or anything like that with open breathers. You need to draw at least 5in/hg to benefit you in any way and that's after the blow-by at WOT. The turbo inlet alone cannot do this unless you have a rediculous restriction. Unless you are willing to spend a lot of money on a mechanical vacuum pump (have to remove ac) or an electric system with check valves left and right then just do yourself a favor and run open breathers and put a check valve between the pcv valve and the vacuum block and be done. If you're gonna go mechanical I would look here Street / Strip Vacuum Pump Kits as they have pumps that can handle constant street use as they use the oil in the air they pull to lube the pump. With this type of pump you will need to eliminate all breathers and pcv.

After talking to racers with evacuation systems they all said they try to maintain vacuum between 5 and 8 inches. Oil is quickly contaminated with fuel when this is done.But there is an increase in hp You would never be able to get this with a system that uses the turbo as the source of vacuum. I agree with your post entirely.

 

[JDEstill]

After talking to racers with evacuation systems they all said they try to maintain vacuum between 5 and 8 inches. Oil is quickly contaminated with fuel when this is done.

eh? Why would oil get contaminated with fuel when running a vacuum in the crankcase? Any fuel that gets in there will boil off a lot easier at vacuum than it will at atmospheric pressure, so I don't get this.

John

 

[unix_punk]

I was also wondering this as the vacuum should be helping the rings seat better which should prevent as much fuel from getting blown by to begin with.

 

[bison]

eh? Why would oil get contaminated with fuel when running a vacuum in the crankcase? Any fuel that gets in there will boil off a lot easier at vacuum than it will at atmospheric pressure, so I don't get this.

John

The added vacuum will pull the fuel right past the rings. It will mix with the oil and wont boil off. Ive seen it myself. Setup had 8 inches of vacuum.

 

[bison]

I was also wondering this as the vacuum should be helping the rings seat better which should prevent as much fuel from getting blown by to begin with.

It increases the ring seal but it still pulls more fuel past the rings. Exactly why, i dont know. But it definitely does.