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Thread: Crank Case Ventilation fully explained. (Turbocharged edition.)

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2011-04-18 14:36:12
#1
Crank Case Ventilation fully explained. (Turbocharged edition.)
Since this is the turbocharged edition of the crank case ventilation thread, I think it needs a few things. Maybe a front mount intercooler, some bigger tires, possibly an upgraded fuel pump. I'll see if I can get someone on that.

In the mean time, let me start off by saying this thread is a companion thread to the Naturally Aspirated edition Crank Case Ventilation thread. You are required to read that thread first, as it has most of the information you need to know in it, and I won't be going over that stuff again here. Go read that thread first, then come back here.
Last edited by BenFenner on 2018-05-13 at 12-39-59.
2011-04-18 17:11:49
#2
Welcome back from reading the naturally aspirated version of the crank case ventilation system. You did read the naturally aspirated edition, right?
Yes?
Okay good.

The main difference between a boosted engine and a naturally aspirated engine for these discussions is that in a boosted application the intake tract can be pressurized above atmospheric pressure. This means that where you used to have zero net pressure, you will have some positive pressure in the intake system. This changes the options of where you can vent the crank case to. You'll want to find new sources of vacuum, and you'll want to make sure you don't accidentally let boost pressure enter the crank case and pressurize it.

Another important factor with most turbocharged engines regarding crank case ventilation involves the intercooler. If the blow-by gasses are routed through the intercooler, the intercooler then in effect gets to act as a giant oil separator. Oil tends to coat the inside of the intercooler decreasing its thermal efficiency. The oil can also build up and puddle, drain into unwanted places, or be consumed by the engine in larger quantities at inopportune times. For this reason, you will see some of the modifications listed in the "BAD" section of the Naturally Aspirated edition (that made little-to-no sense at all on an N/A engine) all of a sudden become acceptable solutions on a turbocharged engine.

There is one more difference between N/A and boosted engines that you should be aware of.
Boosted engines tend to have much higher cylinder pressures than naturally aspirated engines. This produces more power obviously, but it also produces more "blow-by" which you will recall from the naturally aspirated edition of this topic is something we'd like to limit and control.

And don't forget what you learned in the naturally aspirated edition about blow-by gasses increasing your chances of detonation.
Originally Posted by BenFenner
How does blow-by lower your octane? Blow-by gasses with any amount of oil in them will lower the effective octane rating of your fuel because the vaporized oil will ignite at lower energy levels than 87 octane (R+M/2) gasoline. The more of it you allow to enter the cylinder, the more you will have to worry about detonation. This is usually not a big worry for naturally aspirated engines, but obviously forced induction is a different story.


These three things conspire to make ventilating the crankcase of a turbocharged (or supercharged) engine more difficult and more important than on a naturally aspirated engine. Most people don't even bother messing with the crankcase ventilation system on naturally aspirated engines and only wait until they turbocharge the engine to get serious about the system, because now the ante has been raised.

We should start off with a diagram of the factory positive crankcase ventilation system as seen on most common SR20DET engines.



You should first notice one key difference between this setup and that of the naturally aspirated engines. In this setup, the ventilation pathway for the engine blow-by during WOT conditions no longer connects to the intake tract right before the throttle body. The connection is now made before (upstream) of the turbocharger but ahead (downstream) of the MAF. If you think about it for a moment, it makes a lot of sense because the old connection point would just pump pressurized intake charge air into the crank case when the engine is "in boost" which is a really bad idea. The designers had to find a new place to vent the crank case and yet maintain emissions compliance. Venting the crankcase to the intake tract before the turbo is basically identical to venting it to the intake on the naturally aspirated engines. There isn't really much vacuum there during WOT or ever, but there is a slight vacuum and the blow-by gasses get consumed by the engine and the EPA is happy.
Also mentioned before and extremely important to understand is the fact that the ventilation of the crankcase dumps into the intake tract upstream (after) the MAF sensor. This is to prevent any oily blow-by gasses from quickly contaminating and/or ruining the MAF sensor. I'm not going to get into the pros and cons of moving the MAF sensor to the pressure side of the intake tract right now, but suffice it to say, you need to avoid recirculating blow-by emissions coming into contact with the MAF element. (Cars equipped with a MAP sensor as the primary air metering device can ignore this warning.)

It should be said that the factory setup is a very good solution. It is pretty difficult to improve on it, and it is EXTREMELY easy to make it worse. Keep that in mind when considering "upgrades".




Okay. On to the different methods of improving, or completely messing up the factory crank case ventilation system. These methods will cover a huge mix of things I've seen done on people's cars, or that I thought up in my head. Some will be great ideas, some will be good ideas, some will be bad ideas, and some will be awful ideas. I'm going to keep things simple by rating each method on the important points so you can just give it a quick look and see immediately if it's a good idea or not.
Last edited by BenFenner on 2018-05-13 at 12-40-51.
2011-04-18 17:12:21
#3
WOT "catch can" elimination on 1989-1999 engines via cap method:


Effect on the following characteristics:
  • De-clutters the engine bay - Yes
  • Simplifies crank case ventilation system - Yes
  • Maintains stock prevention of crank case pressurization - Yes
  • Stops intercooler from acting as an oil separator - No
  • Helps remove more oil from the air - No
  • Help evacuate the crank case - No
  • Maintains or improves the stock flow capacity - No
  • Helps promote ring seal and prevent blow-by - No
  • Helps prevent oil smoke in exhaust - No
  • Helps prevent dip stick from popping out - No
  • Helps prevent oil leaks due to pressure - No
  • Helps keep intake track clean including throttle body - No
  • Helps keep intake manifold/plenum clean - No
  • Maintains or reduces amount of pollutants - Maybe
  • Maintains prevention of un-metered air from entering the intake - Yes
Consensus: BAD IDEA
Last edited by BenFenner on 2011-12-02 at 21-45-30.
2011-04-18 17:12:51
#4
Venting WOT section to atmosphere on 1989-1999 engines with "breather" filter:


Effect on the following characteristics:
  • De-clutters the engine bay - Maybe
  • Simplifies crank case ventilation system - Maybe
  • Maintains stock prevention of crank case pressurization - Yes
  • Stops intercooler from acting as an oil separator - Yes
  • Helps remove more oil from the air - No change
  • Help evacuate the crank case - No
  • Maintains or improves the stock flow capacity - Yes
  • Helps promote ring seal and prevent blow-by - No
  • Helps prevent oil smoke in exhaust - No
  • Helps prevent dip stick from popping out - No
  • Helps prevent oil leaks due to pressure - No
  • Helps keep intake track clean including throttle body - Yes
  • Helps keep intake manifold/plenum clean - No
  • Maintains or reduces amount of pollutants - No
  • Maintains prevention of un-metered air from entering the intake - No
Consensus: ACCEPTABLE IDEA
Last edited by BenFenner on 2012-07-04 at 17-19-47.
2011-04-18 17:13:11
#5
Adding a "catch can" to the WOT section on 1989-1999 engines:


Effect on the following characteristics:
  • De-clutters the engine bay - No
  • Simplifies crank case ventilation system - No
  • Maintains stock prevention of crank case pressurization - Yes
  • Stops intercooler from acting as an oil separator - No
  • Helps remove more oil from the air - Yes
  • Help evacuate the crank case - No Change
  • Maintains or improves the stock flow capacity - Yes
  • Helps promote ring seal and prevent blow-by - No Change
  • Helps prevent oil smoke in exhaust - Yes
  • Helps prevent dip stick from popping out - No Change
  • Helps prevent oil leaks due to pressure - No Change
  • Helps keep intake track clean including throttle body - Yes
  • Helps keep intake manifold/plenum clean - No
  • Maintains or reduces amount of pollutants - Yes
  • Maintains prevention of un-metered air from entering the intake - Yes
Consensus: GOOD IDEA





*More examples to come.*
Last edited by BenFenner on 2013-02-11 at 00-20-27.
2011-04-19 21:10:07
#6
Originally Posted by BenFenner
Venting the crankcase to the intake charge before the turbo is basically identical to venting it to the intake on the naturally aspirated engines. There isn't really much vacuum there during WOT or ever, but there is a slight vacuum and the blow-bay gasses get consumed by the engine and the EPA is happy.


Even though there is slight vacuum, it should still help. The blow-by air is dumped into an intake pipe that is contained by walls, it has only two locations to go; to the turbo inlet, or to the beginning of the intake where the filter is located. Air is always going to look for the path of least resistance, thus is should go to the turbo inlet even with slight vacuum.
2011-04-20 03:08:01
#7
Bout time Ben

I had actually come up with a solution for my car...Tell me if it's any good or not. Crankcase to lower half of catchcan, cap off "t" going to oem catchcan, other side of "t" goes to top of catchcan and on to intake on turbo. So basically the crankcase will be evacuated into the same catch can as the valve cover and will be sucked into the intake tract like factory. Any good?
2011-04-25 20:33:23
#8
Sorry for the wait everyone. I've at least got one diagram up (stock setup).
I'll have more diagrams up and modifications (both good and bad) soonish.
2011-04-25 20:35:24
#9
Originally Posted by nsusammyeb
Tell me if it's any good or not. Crankcase to lower half of catchcan, cap off "t" going to oem catchcan, other side of "t" goes to top of catchcan and on to intake on turbo. So basically the crankcase will be evacuated into the same catch can as the valve cover and will be sucked into the intake tract like factory. Any good?
I can't visualize this setup. Could you describe it in more detail? Or draw a simple picture?
2011-04-26 15:26:31
#10
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