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I was marveling over the VG this afternoon on the stand in the garage and was pondering ideas on upgrading the PCV system. I autocross my Z a lot and the PCV system, inherent in it's design on the VG, will cause oil to be sucked into the intake and burn off as it passes through the combustion chamber. Not only does this cake up your intake system (throttle bodies, intake plenum, valves, piston, cylinder head, and exhaust tract), but oil significantly lowers the effective octane of fuel when it is introduced into the combustion equation. I believe there is a quite simple solution to this problem. A little intro: The PCV system draws clean air through the crankcase to minimize blowby gases, mainly fuel, which will contaminate oil and break it down. This is not good on bearings at all. Additionally, it is there to prevent the crankcase from becoming pressurized and blowing out seals. It is necessary to ventilate the block for these two main reasons. The "clean" air comes from the two intake pipes that feed into the intake of the turbos. There is a small rubber hose on each side of the engine that feeds air into both of the intake valve covers, just behind the timing belt covers and under the throttle bodies. From there, the air flows into the bottom of the crankcase and back up at the rear of the engine to the driver's side exhaust valve cover only. There are two pipes coming off this single valve cover and the gases are routed with various hoses and pipes to the PCV valves at the bottom of each side of the plenum. The PCV valves are one way valves which will only allow the air from the crankcase to flow into the plenum and the PCV system draws gases through the crankcase only when the plenum is below atmospheric pressure. When you are boosting, the PCV valves will close shut and the PCV system no longer is drawing gases through the crankcase. However, because the PCV valves are closed under high load, the blowby gases in the crankcase now blow out the other end - the intake valve cover ports. From there, it gets sucked into the intake of the turbo and runs throughout the entire intake, intercoolers and all. This coats the entire intake with a film of oil. Because the "exit" for the crankcase gases is only on the driver's side valve cover, during hard right hand turns under acceleration, oil will pool up at these pipes and get blown into the PCV tract. It primarily gets blown into the pipe that feeds the passenger side PCV because the pickup tube is located at the furthest rear of the valve cover. The driver's side PCV pickup tube is slightly forward of the rear of the valve cover. The passenger side of the plenum feeds the driver's side of the engine so you will mainly see smoke being burned off from the driver's side exhaust. Because the air flowing throgh the crankcase comes from the intake pipes, the MAS has metered the air and the ECU is prepared to deliver the corresponding amount of fuel. This is why the PCV system is a closed loop system. I'm going to jump to explanation of a different system in the Z, but there is good reason. -- The AIV system: (Air Induction Valve)
The AIV system is basically a system for putting good oxygenated air into the exhaust tract so that unburned fuel from the combustion process can be burned to keep the catalytic converters hot and emissions down. It is not an air pump though. The way it induces air into the exhaust tract is by way of a reed valve, which only allows gases to flow in one direction. Since the exhaust gases flow in pulses (waves of high/low pressures), there are moments when the exhaust section where the AIV pipes connect (just after the downpipes, or precats) is under a slight vacuum. The reed valves allow the slight vacuum to suck in a bit of fresh air which is then mixed with the bit of extra fuel and burned as it flows through the CAT. When the ECU triggers the AIV system, it also delivers an additional 8% of fuel to richen the mixture and allow for some unburnt fuel. It only operates when you are at idle, when the CATs need an additional means to stay hot. It is safe to eliminate the AIV system but preferrably with an ECU upgrade with "AIV delete". This will keep the ECU from dumping extra fuel into the intake as well as allow you to eliminate the AIV solenoids and bulky AIV hardware. All of the recent JWT upgrades have this (as per Ben at JWT), but check with them on your ECU to see if you have it, if you aren't sure. There is a small sticker on the top of the EPROM inside of the ECU that has a hand written number on it that JWT can reference to see what program you have. Now here's where the PCV and AIV system come together to make a great solution for the PCV system. By eliminating the AIV system, you now have access to an alternate "vacuum" side to the PCV system. Additionally, it will be constant rather than only at idle so it provides a continuous vacuum source. Here's the trick:
1) The two tubber hoses attaching to the turbo intake pipes that feed the PCV system at the intake valve covers can be removed. Do not use the two rubber OEM hoses because they have jets in them that limit the airflow. We want the crankcase to breathe well. 2) Plug up the small fitting on the turbo intake pipes and acquire two small filters (typically seen on Hondas as an aftermarket item) and attach one to each of the two pipes feeding the intake valve covers. 3) Remove the PCV valves and acquire two "plugs" to plug up the holes where the OEM PCV's were. 4) Purchase 8 feet of 5/8" hose from your local auto shop along with 8 hose clamps of appropriate size for that hose. 5) Rotate the PCV pipe 180 degrees on the exhaust valve cover that is furthest forward. Now it is pointing rearward. 6) Cut an 8" piece of the rubber hose and attach it to the side of the PCV valve that is not threaded. Attach the other hose end to the one of the pipes on the exhaust valve cover and clamp both ends of the hose. Attach another piece of hose to the other side of the PCV valve and route it to one of the AIV pickup tubes on the exhaust midpipes. Do this with both PCV
valves. The purpose of the PCV valve still being used is to keep the high pressure part of the exhaust pulsations from blowing air into the crankcase and allowing the vacuum part of the pulses to draw air through the crankcase. What you now have is a PCV system that is entirely independent of the air intake and will perform all of the time rather than only under low load conditions. This design also steps up to demand. Blowby gases are maximized under high load conditions, just when you need the most flow of clean air through the crankcase. Under high load conditions, pressure waves through the exhaust tract are also at their peak with the high and low pressure zones being much greater, thereby creating more "vacuum" to pull air through the crankcase.
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