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Subject PCV System, Explained, Deleted >>>
     
Posted by Ash's Z on April 19, 2011 at 4:21 PM
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Message PCV System: Explained, Deleted

I imagine there are quite a few opinions out there on the PCV system and with the new turbo inlet pipes we are currently right in the middle of producing, it has raised a lot of questions about the option to remove the PCV ports on the accordion section replacements. Please allow me to explain what's up.

The PCV system is a very simple emission control device. It offers nothing in the form of performance whatsoever, and I will get to why it actually hinders performance shortly.

Internal combusion engines all have some degree of blowby at the piston rings which forces fuel, air, and exhaust into the crankcase. These gases also carry oil vapor and mist within them since the crankshaft is spinning rapidly and creating a violent aeration of the oil within the pan. These blowby gases need to be allowed to escape the crankcase otherwise it will build pressure and blow out seals. Up to the late 1960's, all vehicles used a "draft tube" which was located underneath the crankcase which allowed crankcase gases to ventilate out to the atmosphere. This was also why all the roads back then had an oily black strip right down the middle of the lanes. US legislation mandated that all vehicles be equipped with a PCV system which routes these emissions back into the engine intake where they will be burned through the combustion process.

Since the 1960's, engine technology has drastically improved and tighter running tolerances have led to significantly less blowby and production of crankcase gases. Even still, LAW states you must have them.

In our TT vehicles, the PCV system has two sources to draw crankcase gases into the engine intake.

1) PCV valves - located on the sides of the intake manifold
2) Turbo inlet pipes - on the accordion sections

When the intake manifold is in a vacuum state, the PCV valves create suction on the crankcase to draw these gases into the intake manifold directly.

In a boosted condition, the PCV valves close off and the vacuum is created by way of the turbo inlet pipe section. These inlet pipes draw crankcase gases out via the two towers atop the front of the intake valve covers.

Both of these entry points produce the oily film you see within the intake manifold and the crankcase connection to the turbo inlet pipes is why there is always a film of oil all over the inside of the turbo compressor/housing, charge pipes, intercoolers, and throttlebodies.

A couple of things here:

1) Crankcase gases are primarily inert to the combustion process - feeding these back into the engine intake will dilute the fresh air and will lower performance to some degree.

2) The oil mist enters the combustion chamber and lowers the octane of the fuel. This promotes detonation.

3) The oil mist coats the inner walls of the intercoolers, thus lowering their thermal efficiency.

4) The oil mist coats the throttlebody plates and gums them all up over time. (the PCV system is the only reason you ever have to clean the TBs)

5) If you drive your Z hard you will find that in hard left hand turns where you are pedaling the accelerator you will often get huge plumes of oil smoke from the exhaust. This is because the oil will pool in the back of the driver's exhaust valve cover and get sucked into the PCV valves and enter the intake manifold. You will usually hear severe detonation when this occurs as well.


The real kicker to all of this is that our engines seal up exceptionally well compared to a 1960's pushrod engine. They are manufactured with much tighter tolerances and superior materials that will last over very long durations of time before parts begin wearing enough that blowby becomes an issue. I've taken apart 300,000+ mile VG's before and you can still see the original hone marks in the cylinder walls and the pistons pop right out the top of the bores without having to use a ridge reamer. This fact combined with all the drawbacks of using a PCV system overwhelmingly suggest to remove the system.

PCV System Deletion:

I know there are other methods that have been documented before. I am only describing the method I have always used to accomplish this. It is simple, doesn't take very long to do, and is very inexpensive.

You need the following items, which you can pickup at any auto parts store.

(2) 1/4" NPT plugs (to replace PCV valves)
12"length, 1/2" inner diameter heater hose
(4) 1/2" inner diameter rubber caps
(2) Small breather filters - they look like miniature POP chargers
(2) 1/2" to 1/2" male-male hose barb connector

First thing to do is to remove both turbo discharge pipes.
Remove both PCV valves and hoses that connect to them.
Install the pipe plugs into the PCV holes in the intake manifold
At the back of the driver's exhaust valve cover there are two ports for the PCV pickup. One points forward and the other points across the back of the engine to the passenger side. Remove the hoses from each and cap them.
Remove the rubber hoses that connect between the accordion section and the pipes coming from the intake valve covers.
Cap the ports on the accordion hoses.
Cut two 4" long pieces of the 1/2" rubber hose and install the 1/2" barb connector into the hoses.
Install the breather filters to the hose barbs
Install the 1/2" hoses with the filters - attach them to the metal pipes coming off the intake valve covers.

Reinstall the turbo discharge pipes and you are ready to go.

In this configuration you have eliminated the crankcase gases from entering the engine intake. The crankcase will open ventilate through the breather filters you attached to the intake valve covers. The intake valve covers are heavily baffled internally to prevent oil from making its way to the PCV towers that the metal pipes connect to so no worries about oil puking out of the filters.

Over time you will notice some small accumulation of oil on the breather filters. This is the oil mist that does make its way out of the crankcase, but it is a very small quantity and cleaning the filters when you change your oil will be more than sufficient, if even that often.

I personally dont even run the breather filters - I have also removed the metal pipes from the intake valve covers and I just leave them wide open. I've been doing this now on this engine for 50K miles and did it on my previous build for some 60K miles. About once every few months I'll re-polish the plenum and wipe up the very very small amount of oil film around these ports. My throttlebodies are just as clean as they were when I put the 60mm units on, there is no oil film on the inside of my inlet pipes, charge pipes, intercoolers or intake manifold.

I am just one person who has done this process to his own car and have done this on a number of other customer vehicles with the same successes. I know there are other options out there that people use - I cannot speak for those approaches as I've never done it that way. All I can say is that this method works exceptionally well and is one of the simplest deletion processes you can do with these cars.

So, the option to have the PCV port on our accordion replacement sections should be obvious now. No reason to have to cap yet another unused port, not to mention, without the port you have extra room for the breather filter.

Here's a couple of pictures I took just to show the filters and another method of blocking the ports on the valve cover.



If you have the valve cover off, you can remove the two metal elbows from the valve cover and tap them out with a 3/8" NPT tap. Drill out the baffle within the cover so you can get rid of the metal shavings and plug the holes with a pipe plug with some teflon tape.


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