PCV |  | Catch |
PCV | | Catch |
This mod will prevent oil from condensing in your intercooler by rerouting the normal PCV ventilation system through an atmospherically vented filter instead of back through the intake system. (Note that this is for racing-use only)
Background
The goal of the PCV (Positive Crankcase Ventilation) system is to simply relieve the pressures which build up in the cylinder head due to pressurization of the crankcase. You see, as the piston is pumping up and down in its respective cylinder, you might think that the only pressure it's creating is that due to the compression of the intake mixture. You'd be incorrect. You also have to take into account the compression occurring on the back side of the piston on the downward stroke. This, plus the small blowby past the piston rings (or large amount if your rings are shot) lets gases enter the crank case area where your crankshaft is pumping away. Since the head is joined to the crankcase via the oil return ports, the cam galleys would become pressurized as well if no purging system existed. If the engine was a closed system, this pressure would build up and would eventually start rupturing seals and blowing oil all over the place. That's where the role of the PCV system comes in.
The crankcase is vented into the head via a number of channels. The primary one is a hose at the front of the motor just under the oil filler cap. Also, gases can get in via the low pressure oil drainback holes along the head as well as through the high pressure oil intakes coming from the oil pump, albeit in a much smaller amount. The only exit for these pent up gases is through your various seals or the breather hose barb on the top of each valve cover. The breathers can technically be located anywhere in the engine, but are put here since this is the best place to keep oil losses at a minimum. The barbs are baffled within the cam cover to try and keep mostly vapor coming out.
In the normally aspirated Supra, as with any normally aspirated car, these vented are plumbed into the intake near the throttle body. This effectively burns any excess gases which escape in the combustion process. However, in the turbo Supra, and again as with any turbocharged car, you have an additional problem to worry about -- intake plenum pressurization. If a turbocharged car was only connected to the throttle body, every time the car hit positive boost pressure, the pressure would effectively pressurize the PCV system and force additional air into the motor -- and I don't mean where it should be going :-). That's why the turbo Supra PCV pipe is connected to both the throttle body and the intake pipe (before the turbo). That way, under boost pressure, the pressurized air coming out of the throttle body now will take the path of least resistance and skip past the valve covers and instead vent to the intake (accordian) pipe. This will also create a low pressure area over the hose barbs and generate a slight suction to pull out any excess pressure in the head.
Now the bad thing about this for turbo owners is that this hot compressed gas (HC) contains vaporized oil in it which will condense on (or in) the first cool thing it encounters. In our case, that's the intercooler. The intercooler is doing nothing wrong. It's simply doing its job and cooling down the intake charge which is heated from the compression and conduction action of the turbo. But once that oil vapor reaches that point, it'll condense into a liquid again and begin making an oily film on the inside of your intercooler and piping nearby. I've heard accounts from many turbo owners (of various makes and models) about actually pouring out oil from their intercoolers. Also, the induction of this hot vapor will dilute the nice cool air mixture being drawn in and raise the octane requirements of the motor and lower the power (albeit slightly).
Now since I upgraded to the HKS Intercooler and Hard Pipe kit, I didn't want to ever see my new baby filled with oil. Plus, it makes sense to keep from contaminating the intake charge with oil vapor when you could use the same wasted volume for additional air into the motor. Therefore, I made some measurements and did some searching around for a catch can. I could have simply mounted a pair of K&N filters directly on the valve covers, but they would turn brown and oily eventually and the oily mist would get on the surrounding components quite quickly. A catch can would prevent this.
Catch cans are used, and have been used in racing for many years. Basically, they serve to catch and condense the vapors coming off the valve covers. They're mandatory in racing to prevent various engine liquids from leaking out on the track and causing havoc to a traction dependant environment. On race cars, you'll see them on many more systems than just the PCV.
The "Mod"
The primary problem in the Supra engine bay is the lack of room to mount anything. I did a lot of research and searching to find something which would work. I even made some drawings for a can which could be fabricated. I had everything down to the custom brackets on there. Unfortunately, after pricing it out, it would cost nearly $500 for a prototype and a few hundred for more thereafter. But, after searching for a few months, I finally heard about Jaz Racing products Mini-Breather can. It's designed primarily for serious go-kart racing, but appeared to be perfect for this application. All of my goals were met. These were:
As you can see in the following pictures:
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Jaz Can (Front) | Jaz Can (Back) |
To order one of these cans, you can get them directly from Jaz by calling:
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800-525-8133 |
and ordering:
The breather comes with molded in 1/4-20 threaded inserts and a swivel petcock for each draining. It has two 3/8" hose barbs, one on each side and comes with a bracket to mount it to a rollbar (although this can be modified for Supra usage). I listed both the white (natural) part number which I ordered as well as the black one in case you have a color preference.
The Installation
The installation went fairly quickly. The biggest problem I had to overcome was getting an adequate amount of 3/8" Purosil to route everything smoothly. I found a bunch eventually though and got it done. The only place I could find in the engine bay where I could utilize stock mounting hardware (so I could maintain backwards compatibility plus not make hole in the car) was right off the primary fuse block behind the battery. The can slips nicely next to the block, between it and the alternator. It allows easy access to draining excess oil condensation as well by sticking a small can or something in there.
I knocked off a couple of pics showing the installation below:
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Jaz Catch Can Instl Pic #1 | Jaz Catch Can Instl Pic #2 |
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Jaz Catch Can Instl Pic #3 | Jaz Catch Can Instl Pic #4 |
Results
Immediately after installing it, you'll notice the computer has to recalculate for this unmeasured air leak you've created, in effect. I noticed after a day or so of recalibrating by the ECU, the car actually idled noticeably smoother (strangely enough). Unfortunately, while calibrating my VBC, I smacked fuel cut and had to reset my ECU to erase the stored codes. After fully resetting the ECU and making it start from its default baseline, the car now ran noticeably rougher at idle (although no different while cruising). From what I've read, the further the car is away from stock calibration, the longer it takes the ECU to reach optimal, so don't worry if your car runs strange for a little while after doing this. It'll correct itself. Mine stalled out the day after the reset when I put it into neutral at a light and it tried to maintain a 450 rpm idle :-).
You'll also notice, occasionally, some excess wispy vapor coming out of the K&N if you watch the can with the car idling. This is normal excess moisture getting released from the oil combined with vaporized oil and blowby HC (hydrocarbons). It's this hot mixture that you're no longer trying to burn in vain. And lastly, you'll notice a smell of hot oil/gas coming from the can and your engine area in general. Basically, the car will smell a little like an old muscle car, which also used open PCV systems to maximize power in a day of lesser EPA restrictions.
I've also noted that you have to keep somewhat of an eye (although not an extremely close one) on the can to monitor the vapor. Once the K&N becomes super saturated, the resultant condensation on the filter can make the outside of the catch can rather grimey. Just clean your K&N every few months and you should be able to avoid this. I'm always working on further refinements to this and all my mods, so watch the mods page for further developments. Perhaps I can implement something else to extend the maintanence intervals.
In the end, I think the benefits greatly outweight the losses here. These benefits are:
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