Anyone completely removed the PCV system before?

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MalcolmV8
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Anyone completely removed the PCV system before?

Post by MalcolmV8 »

Without getting into all the complex details of why (turbo'd car) I want to see if anyone has completely removed a PCV system from a car so that the intake is no longer drawing air through the crank case of the motor. I hear from a lot of people that this air been drawn into the intake is more than just emissions but also sucks the engine's blow by gases out of the crank case and keeps sludge from forming. Any truth to this?
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Re: Anyone completely removed the PCV system before?

Post by Dave »

Closest think I can think of is the cars before emmisions, used what was called a "road draft tube.
Usually mounted on the back of the intake manifold and the tube went down below the engine. End of it was cut as to suck the fumes from the crank case area. Goes back before '66' in Cal.
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Re: Anyone completely removed the PCV system before?

Post by MalcolmV8 »

Right, I've heard of that too Dave. The issue is with this turbo car two valve cover vents go to a catch can (which catches a lot of oil) and the block itself vents to the bottom of the catch can and doubles as a drain back to the block when not in boost or when the car is shut off. Otherwise I'm emptying this catch can twice a day. This leaves no provisions for running a PCV system. If I really need to run a PCV system I will have to pull the oil pan off (easier said than done) and weld in an oil return there and use the vent on the block to go to a PCV system with a check valve to the intake. Trying to weigh my options here. If the PCV system is purely emissions I have no problem ditching it but if engine sludge is a reality then I guess I need to start tearing things apart and going through a redesign.
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Re: Anyone completely removed the PCV system before?

Post by cgrey8 »

PCV has the benefits you mention and another you didn't.

The first is the emissions benefit. Blow-by from the rings gets into the crank case and if it isn't drawn into the engine will get out into the atmosphere (an emission). So for reducing emissions, the EPA wants that drawn into the engine to be reburned. However this also has the benefit of preventing the 1/2 burned exhaust and raw fuel from collecting in the oil. The oil will pick up some of it, but if you dilute the crank case mix with fresh air, the far less of the blow-by ever comes in contact with the oil thus dramatically reducing the build-up that does get into the oil. This is why Propane and CNG fueled vehicles can go so much longer on oil changes. The blow-by doesn't have liquid raw fuel or soot to contaminate the oil. Also Propane and CNG don't produce combustion acids which also contaminate oil. Thus you can easily go 20kmiles with quality oil in a CNG-fueled engine.

The other benefit you didn't mention is that pulling vacuum on the crank case thins the air in the crank case. A thinner air mix produces less wind-drag on the crank, connecting rods, and pistons. I've heard of drag cars having a high volume vacuum pump to pull a hard vacuum on the crank case to thin the air in the crank case during a pull down the track. Evidently the drag put up by the windage is enough to make the added weight of an additional vacuum pump worth it. Obviously you don't get anywhere near that deep of a vacuum on the crank case when setup "properly." And unfortunately you get none of the benefits at WOT since at WOT, there is no engine vacuum to pull on the crank case.

But your turbo'd setup does bring up another good point. Super/turbocharged engines don't generally use a standard PCV valve. Boosted applications usually use PCV valves with integrated back-flow check valves to prevent intake boost pressure from pressurizing the crank case.
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Re: Anyone completely removed the PCV system before?

Post by plowboy34 »

Yes the pcv will help keep sludge from forming, it helps to keep moisture from building up due to temperature differences between the inside and the outside of the engine. I have been building engines from the old draft tube days(as Dave has mentioned) to the pcv systems and it is a major difference in how much cleaner the engines are. Also I believe a pcv system would help with the catch can filling up as it will keep the pressure inside the engine lower which will help keep the oil from venting through the valve cover vents. No science to the last thought just some Plowboyology
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Re: Anyone completely removed the PCV system before?

Post by MalcolmV8 »

cgrey8 wrote:PCV has the benefits you mention and another you didn't.

The first is the emissions benefit. Blow-by from the rings gets into the crank case and if it isn't drawn into the engine will get out into the atmosphere (an emission). So for reducing emissions, the EPA wants that drawn into the engine to be reburned. However this also has the benefit of preventing the 1/2 burned exhaust and raw fuel from collecting in the oil. The oil will pick up some of it, but if you dilute the crank case mix with fresh air, the far less of the blow-by ever comes in contact with the oil thus dramatically reducing the build-up that does get into the oil. This is why Propane and CNG fueled vehicles can go so much longer on oil changes. The blow-by doesn't have liquid raw fuel or soot to contaminate the oil. Also Propane and CNG don't produce combustion acids which also contaminate oil. Thus you can easily go 20kmiles with quality oil in a CNG-fueled engine.
Yes the blow by is what I'm concerned about. It definitely contaminates the oil. Before rebuilding the engine I removed the PCV system and ran that way for a couple oil changes and I noticed the oil turned black and nasty really quick after an oil change. Will that turn to sludge in my engine though? I don't know. I run mobil 1 full syn and have been changing every 3k (often sooner because of working on it). So if the oil just dirty'd quicker and required more frequent changing then I could live with that as I change the oil frequently anyways.
I've also read that when the engine gets up to operating temps and the oil is hot it burns off the moisture and fuel in it anyways.
I wish I could find some definitive test results.
cgrey8 wrote: The other benefit you didn't mention is that pulling vacuum on the crank case thins the air in the crank case. A thinner air mix produces less wind-drag on the crank, connecting rods, and pistons. I've heard of drag cars having a high volume vacuum pump to pull a hard vacuum on the crank case to thin the air in the crank case during a pull down the track. Evidently the drag put up by the windage is enough to make the added weight of an additional vacuum pump worth it. Obviously you don't get anywhere near that deep of a vacuum on the crank case when setup "properly." And unfortunately you get none of the benefits at WOT since at WOT, there is no engine vacuum to pull on the crank case.
I'd have to disagree on this. I could be wrong but honestly the PCV system pulls such a small amount of air out of the crank case I don't see how it could possibly even come close to creating a vacuum in the crank case. At best it slowly moves air which would pull blow by gases out. Even if the suction through the PCV valve (which acts as an air metering device as well) was strong enough to create a vacuum and reduce drag on the crank etc. I would only see the benefits at idle and extremely light throttle and light cruise on the highway. While driving around the turbo is so quick to try and spool all the time my vacuum gauge seems to swing from vacuum to 0 a lot.
cgrey8 wrote: But your turbo'd setup does bring up another good point. Super/turbocharged engines don't generally use a standard PCV valve. Boosted applications usually use PCV valves with integrated back-flow check valves to prevent intake boost pressure from pressurizing the crank case.
Yeah in my specific setup I have standard PCV valve with a brass check valve plumbed in line to stop boost from over powering the PCV.

I think I'm leaning towards just doing it the "hard" correct way and pulling the exhaust and turbo down pipe, dump tube etc. and removing the oil pan and baffles etc. and welding in fitting for oil return and keeping my PCV system functional.

There is one downside to keeping the PCV system though. This means I can't run the block vent hole to the catch can and vent the block because that hole is used to plumb the PCV system. Some people I've spoken too think the amount of blow by under boost is more than what can pass from the crank case to the cylinder head and out the valve cover holes. I've looked at the two oil passages/vents between head and crank case I think there is some merit to what they say. One solution I though of is while I have the oil pan off put a second fitting on it facing the front of the car above the oil level and run it to the catch can. That would vent my block.
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Re: Anyone completely removed the PCV system before?

Post by MalcolmV8 »

plowboy34 wrote:Also I believe a pcv system would help with the catch can filling up as it will keep the pressure inside the engine lower which will help keep the oil from venting through the valve cover vents.
In an n/a motor I could see that been a possibility but on a boosted motor the PCV system shuts down as soon as you go into boost to stop you from pressurizing the block and the blow by while under boost is pretty heavy and what causes all the oil to push out.

When I drive around out of boost the catch can collects pretty much nothing but when I run it hard it starts collecting pretty quick.
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Re: Anyone completely removed the PCV system before?

Post by cgrey8 »

MalcolmV8 wrote:...I'd have to disagree on this. I could be wrong but honestly the PCV system pulls such a small amount of air out of the crank case I don't see how it could possibly even come close to creating a vacuum in the crank case. At best it slowly moves air which would pull blow by gases out. Even if the suction through the PCV valve (which acts as an air metering device as well) was strong enough to create a vacuum and reduce drag on the crank etc. I would only see the benefits at idle and extremely light throttle and light cruise on the highway. While driving around the turbo is so quick to try and spool all the time my vacuum gauge seems to swing from vacuum to 0 a lot...
Yes, and yes.

Yes, the vacuum on the intake is very light. But any reduction in pressure will reduce windage drag at the speeds a crankshaft and pistons move. And the benefit is ONLY seen while cruising to get a tad better fuel economy on any vehicle using the engine for PCV circulation. Just to give you an idea of the rate air thins, consider how large the earth's atmosphere is. Private (unpressurized) planes can fly to about 15,000 feet. Larger commercial planes can fly to over 40,000 feet. And high speed military jets can fly a known 80,000 feet and believed to fly higher, but the details are often classified. For the commercial and military jets, most people focus on the fact that they can fly that high and think that's impressive. But in actuality, they HAVE to fly that high to go the speeds they want to go. Any lower, and the wind resistance is too great and they can't attain their target speeds. My point to all that is there's air 80,000 feet above the earth and further. But 1/2 of ALL the air molecules in the atmosphere exists below 5000 feet. That's how quick air thins. At sealevel, average atmospheric pressure is 14.7 PSI (29.92"wc). In Denver, the pressure is closer to 12.1 PSI (24.63"wc). So as it relates to engine windage, it doesn't take much change in pressure to thin the air enough to be significant to fuel economy. Obviously more vacuum is better in the crank case, but to get more vacuum would require the engine produce more vacuum. And since the PCV system's primary function is to keep the crank case vented with fresh air, windage fuel economy benefits are just icing on the cake, not something that is targeted as something to enhance or optimize.

But as you said under heavier throttle, there's very little PCV flow. And while at boost, there's none. It is unfortunate that when you need PCV flow the most is when you have none. But it is what it is. The assumption being you are only at WOT for short periods of time anyway so the PCV system will start back up nearly immediately after the WOT to help drag out the blow-by. However it doesn't surprise me that your oil gets dirtier with harder driving because of the higher amount of blow-by that happens at more aggressive driving conditions.
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Re: Anyone completely removed the PCV system before?

Post by MalcolmV8 »

cgrey8 wrote:In Denver, the pressure is closer to 12.1 PSI (24.63"wc). So as it relates to engine windage, it doesn't take much change in pressure to thin the air enough to be significant to fuel economy.
I don't think the thin air in Denver is causing good fuel economy but reducing windage on the crank shaft. I'd think it's the lack of air going in the engine means less fuel squirted that's causing that. Honestly I've never checked fuel mileage at higher altitudes but I do know when I drive up into the mountains my v6 rental cars feel like 4 cylinders. They are so powerless and when you get back to sea level or close to it the difference is significant. It feels like the engine just suddenly comes to life. Just shows how little air is getting into the engine at altitude.
cgrey8 wrote:Obviously more vacuum is better in the crank case, but to get more vacuum would require the engine produce more vacuum.
Not necessarily as the engine already produces more than enough vacuum. The majority of normal streetable engines produce plenty of vacuum in cruise or idle but the PCV valve also acts as a metering device limiting how much air is pulled from the crank case. It pulls very little because of it. Ever tried removing the PCV valve and replacing it with a hollowed out tube that's not metering the air flow? I have. Air flow is suddenly increase dramatically but it also acts like a vacuum leak and the my engine would idle at 1800 rpms instead of 850 because of all the excess air it could now pull in.

Also more vacuum is only good to a certain point. I forget the magic number but I think it's 7 hg of vacuum max is all you want in the crank case. Anything more and you start sucking oil off of critical components in the valve train and worse. I bet the guy who figured that one out was bummed. You'd fry an engine in seconds that way I'd imagine by sucking off all the oil.
cgrey8 wrote: And since the PCV system's primary function is to keep the crank case vented with fresh air, windage fuel economy benefits are just icing on the cake, not something that is targeted as something to enhance or optimize.
Speaking of I have seen some exhaust pipe setups where you have a small pipe in the exhaust at an angle and the idea is at WOT the exhaust gases flowing by the tube will create a low pressure on the tube and a vacuum which runs up to your valve cover to try and reduce windage in the engine. Most articles I've seen that tested this though found marginal results at best and a lot of issues to work around such as dealing with extremely hot tubing coming off of the exhaust, check valve requirements so normal cruise or idle is not pushing exhaust gases into the crank case, and some sort of inline catch can method to stop it sucking in oil and burning it in the exhaust under WOT causing a smelly oil smell.
cgrey8 wrote: But as you said under heavier throttle, there's very little PCV flow. And while at boost, there's none. It is unfortunate that when you need PCV flow the most is when you have none.
That's where the exhaust method mentioned above would be somewhat useful but from what I've read it's not worth the troubles. The article I read even had a vacuum gauge hooked up and read minimal vacuum. Slick concept though if you could work out the bugs in it. Personally I have a very large free flowing exhaust that would not produce enough velocity I don't think to create a good low pressure on the tube.
cgrey8 wrote:The assumption being you are only at WOT for short periods of time anyway so the PCV system will start back up nearly immediately after the WOT to help drag out the blow-by.
Yup that's exactly it. In fact when the breather from the catch can was up in the engine bay I could smell the oil smelly fume smell in the car. However in idle and normal cruise I couldn't smell anything because the PCV system was pulling air in through the catch can into the engine and eventually the intake. When I'd get into boost the PCV system would shutdown and blow by gases would now be escaping though the catch can and I'd smell that horrible smell. Once I got off and went back to normal cruise the PCV would kick in and the smell would go away immediately. Shows me the PCV does indeed change direction of the air.
When I was experimenting and removed the PCV system completely I could smell that nasty oil smell constantly. I eventually put the PCV system back and then routed the breather on the top of the catch can to the underside of the car and I now smell nothing.
cgrey8 wrote: However it doesn't surprise me that your oil gets dirtier with harder driving because of the higher amount of blow-by that happens at more aggressive driving conditions.
That's true I'm sure by my observations where not when driving hard but when removing the PCV system completely. I noticed I'd do a fresh oil change and within a couple hundred miles (I forget exact mileage but it was not much) the oil seemed black and dirty already. Mind you that was on a 180k mile turbo'd motor that was tired. Installing the PCV system and then doing an oil change it took much longer before the oil changed black. These were just general observations. I probably should have kept accurate logs but those weren't specific things I was testing for at the time, just observations I noticed while doing other stuff.
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Re: Anyone completely removed the PCV system before?

Post by cgrey8 »

MalcolmV8 wrote:...I don't think the thin air in Denver is causing good fuel economy but reducing windage on the crank shaft. I'd think it's the lack of air going in the engine means less fuel squirted that's causing that. Honestly I've never checked fuel mileage at higher altitudes but I do know when I drive up into the mountains my v6 rental cars feel like 4 cylinders. They are so powerless and when you get back to sea level or close to it the difference is significant. It feels like the engine just suddenly comes to life. Just shows how little air is getting into the engine at altitude...
Your comment is correct that you get better fuel economy at altitude because of less air going into the engine. But the connection between lower air pressure and less fuel demand isn't telling the whole story.

Just this November, my wife and I went to the Grand Canyon where we had to drive an underpowered Fiesta from Phoenix up to the 7000' elevations of the south rim. While there, I noticed the onboard computer was calculating our fuel economy driving around Flagstaff and the Grand Canyon area much better than when we were doing similar driving in Sedona and Phoenix. I was puzzled by this and verified what I was seeing a few times. And I got to thinking about these very same topics of PCV and avionics...hence why the topic is fresh on my mind for regurgitation here.

The reasons for the better fuel economy are obviously related to the altitude, but often not for the simple reason that there's thinner air so less air can get into the engine. It's not that simple. Fact, an engine needs a certain mass (not volume) of air matched with a certain mass of fuel to do a certain amount of work. The work to do is to run the engine. The main task is obvious...to produce torque to push the car. The less obvious work being done is the work to run the alternator, water pump, oil pump, fan (whether electric or mechanical), overcome windage & pumping losses in the crank case, transmission, etc. Now it is true that the engine's max torque (WOT) will reduce at altitude due to the thinner air. But while at non-WOT loads (loads attainable at both sealevel and altitude), the engine needs the same mass of air and fuel to do a given amount of work. The throttle plate will have to be open further at altitude than at sealevel in order to attain the same mass air flow hence why a vehicle might feel doggish & non-responsive even if you aren't WOTTing it.

So how does being at altitude get you better fuel economy? It's a few things with a MAJOR one that's the main contributor. Sure, reduced atmospheric pressure results in lower windage losses which reduces the amount of fuel needed at altitude. And with lower atmospheric pressure, the exhaust system doesn't have to work as hard to push the exhaust out into the atmosphere. And if the fan has to turn on/is spun by the engine directly, the fan doesn't work as hard cutting the blades through thinner air. Although in this case, less air is actually being pushed across the radiator. While all these, and probably a few more not mentioned, will contribute to improved fuel economy. But the biggest contributor to better fuel economy is the same reason airplanes have to fly higher to go faster. The thinner the air, the less wind resistance for any given speed. So less work is done to push a car through the air at the same speeds. That's where most of the fuel economy benefits are to be credited.

I don't have a feel for just how much the other things contribute to the reduced load, but I wouldn't be surprised if a GM or Ford engineer told me it's less than 5%. If that's true, discussion of improved fuel economy due to reduced PCV windage is anecdotal at best, but interesting to think about.

But racing is different. Every HP counts. There's a clear difference between a stock daily driver cruising at sub 2500 RPMs and a race-engine reving 6000+RPMs. So if in those scenarios, crankcase windage IS a source of significant friction loss, it doesn't surprise me that you might see a sealed race engine with a vacuum pump pulling as hard as it can to evacuate blow-by air in an effort to gain a few HP. As long as the HP gain justify the added weight, that's all that is needed and ways to evacuate the crank case will get thought of, such as your exhaust venturi idea.
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Re: Anyone completely removed the PCV system before?

Post by MalcolmV8 »

Yeah wind resistance or lack there of in the mountains makes sense. Interesting stuff.
92 302 Ranger - sold
94 302 Ranger AWD - sold
07 BMW 335xi - tuned, boost turned up, E85 - sold
04 911 TT - to many mods to list. Over 600 All Wheel HP on pump gas - sold
2015 Coyote - daily driver
03 Cobra - 2.3 TVS on a built 12:1 CR motor with ported heads, cams, long tubes etc.
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