Quote »-----------------------------------------------------------------------------------------Intake Manifold Vacuum Assisted Ventilation----------------------------------------------------------------------------------------
In Turbocharged vehicles the Intake manifold sees both vacuum and boost pressure unlike in naturally aspirated cars. The PCV valve acts as a check valve blocking any pressure in the rare occasion their is backfire in the Intake Manifold. I have heard that some individuals placing a check valve in-line and allowing the Intake manifold to assist in ventilating the crankcase. The check valve insures that boost pressure doesn't enter into the crankcase through this line.
Ideally one would want to induce a gradual amount of vacuum up to 15 in/hg under full load. Connecting the evacuation line to the intake manifold would do the exact opposite of this. On a boosted vehicle the Intake Manifold will read 25in/hg at idle and 20-15in/Hg in low load conditions and quickly disappear when any moderate to high load conditions appear.
In a stock vehicle this is acceptable because the PCV valve meters the vacuum as shown:
Idle, Low load--- high vacuum pressures fully retract the pintle causing only a small vacuum draw on the crankcase.
Mild load conditions--- vacuum present in the intake manifold is not as strong so the pintle sits in the middle of the pcv valve allowing more vacuum to evacuate the crankcase.
High load + WOT conditions--- their is almost no vacuum present and the pintle is almost completely extended allowing the most amount of gasses to be drawn into the intake manifold.
Engine backfire--- the pintle fully extends and seals to eliminate any gasses from flowing from the intake manifold to the crankcase.
Not only are you pulling excessive vacuum at low load conditions you are contaminating the Intake charge with oil and unburnt fuel blow-by.
I cannot recommend this setup to anyone.
-----------------------------------------------------------------------------------------Intake slashcut evacuation-----------------------------------------------------------------------------------------
Using a slashcut tube to create vacuum is an old trick which works on the Bernoulli effect as air rushes past the tube at high velocities. Make sure you place the slash-cut opening in the opposite direction of the airflow.
One method for evacuating the crankcase is to allow the Intake(pre-turbo) to draw out these gasses. In my tests their was a linear load dependent vacuum drawn using this method. None to insignificant amount of vacuum drawn at idle and low load conditions, moderate load created 0.25 psi(0.5") of vacuum, and high load/WOT created a maximum vacuum of 0.5 psi (1") vacuum. One does not need to use a check valve with this approach as their is never any reason for pressure to force its way into the crankcase.
Their is a positive and negative aspect to this approach. The great thing about this method is that it is the only method which allows one to completely eliminate any blow-by gasses from contaminating the environment. The downside is that it contaminates the Intake charge with a used air charge.
Judging from the amount of contaminants I collected in my open breather catchcan every 2-3 weeks it would be absolutely insane to use this method without a sealed(no open breather element) and baffled catchcan in-line between the crankcase /valve cover and the intake. Keep in mind that most of the contaminants will be sucked into the intake as opposed to only some contaminants trapped in an open breather catchcan while the rest pollutes the environment.
Bottom Line
Cost: 20-150 dollars(dependent use of catchcan and welding)Performance: Good(as long as the compressor housing/Intercooler are cleanedperiodically and a catchcan is used)Reliability: Good.Environment: Excellent(provided that you use no other open breather elements)
-----------------------------------------------------------------------------------------Exhaust slashcut evacuation-----------------------------------------------------------------------------------------
This is based upon the same Bernoulli effect mentioned before but uses exhaust gasses to draw out crankcase gasses instead.
Their are 2 ways of doing this:
1) Weld a slashcut tube in your waste-gate dump-tube2) Weld a slashcut tube in your exhaust
In the first test I connected my Dewyer Magnehelic Pressure Gauge to the slashcut in my wastgate to measure the vacuum draw. As expected I only saw maximum vacuum drawn when the wastgate was open after reaching my maximum boost pressure set on my boost controller. The amount of vacuum went up from 0.25psi(0.5") to 0.4(0.8") vacuum. The numbers shown here were very similar to those shown with the Intake slashcut with the exception of being present when the wastgate started to open.
I chose to connect my valve cover breather and top port (oem- not modified plugs) on my block to the waste-gate slashcut tube. Check valves aren't really needed here but you can use one if it make you feel better.
For my second test I welding in a slashcut tube in my downpipe(12" from turbo). At first I had problems melting my high temp tubing with the heat from the downpipe and exhaust so I soldered together some copper pipe to solve this problem. I placed a check valve in-line on the top 6 inches of hose and wrapped it in reflective heat wrap as you can see.
At Idle the Dewyer Magnehelic Pressure Gauge showed 0.1-0.2psi of vacuum. Driving around town was more unpredictable. The gauge would oscillate between positive pressure(when i tested without the check valve) to 0.5 psi (1") to 1.1 psi ((2.2"). It rarely displayed positive pressure but I could find no simple pattern either rpm or load dependent. Typically it would bounce around 0.6psi to 1psi.
Here is a picture of the hose connected to the valve cover port without being tested. You definitely want to run a one way check valve in-line here.
I purchased the check valve for 1 dollar at a local junkyard. You can find the check valve in-line on the brake booster line on any honda.
Another source for a check valves and slashcut tubes(In case you don't feel like cutting your own is Moroso:
Bottom Line
Cost: 20-80 dollars (dependent upon if you have it welded or not)Performance: Great.Reliability: Great.Environment: Poor. [/quote]The only thing i dont agree on is that he says when using the intake method that you would have to clean the compressor and the intercooler because it would get dirty. I ran my valve cover straight to my turbo intake with no catch can for probably 8K miles and when i decided to change my setup my turbo compressor/fan was still clean. I guess i didnt have much blow by but, if you have a good catch can i dont think that would be a problem.
Cjmartz2k wrote:I'm pretty interested in this exhaust routing thing. I'm sitting around mid 500hp at the wheels AND I have a tired motor with a lot of blow by (actually I think I have a cracked head). I'm still struggling to see how the exhaust pulls gases out of the crankcase. Can you elaborate? I'm mostly just looking to remove the smell emanating from under my car (I vent right onto the road just like most here on Okinawa, I don't care, kiss my ***). How could it help hp wise also?
I might just re-route the hose into the same box/area as the intake. The "drippin's" could still fall down below the car, but the stank fumes could float up from one area into another into the intake. It's really only smelly at idle when the car isn't moving.
For high HP applications i would not use the intake method because you dont want the blow by gases to get back into your intake. It can lower the octane of your fuel and cause problems. For street cars its no big deal imho.