PCV 101 for Forced Induction 80's

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BACKGROUND
I have put in many aftermarket turbo and superchargers over the years, and repaired many hose routings of just stock turbochargers as well whilst working on those darn quattros. One of the biggest issues I have dealt with over the years is boost vs PCV systems. Especially in aftermarket add ons, it becomes a important issue to engine seal longevity. After seeing some familiar signs of PCV induced seal blowout on my Supercharged 80, I decided to look harder at the PCV design and possible modifications.

DESCRIPTION
The 80 uses a dual PCV system (1994 FZJ80). There is a idle PCV (IPCV) that goes to the PS of the valve cover then to the throttle body. Then there is a manifold runner PCV with valve (MPCV) that goes from the DS valve cover (with valve inserted) then routed to the manifold runner. In stock trim (no SC) the idle PCV drops vacuum from the tbody port with increase rpm. The vacuum in the manifold PCV then draws up the valve ball, and PCV function changes from throttle to manifold vacuum. As the manifold vacuum decreases, the ball in the valve seals back up, and the PCV function changes back to the TBody.

The reason for PCV, is to keep the crankcase and the head under vaccuum. This also allows blowby gasses and moisture to get recirculated into the intake manifold. Without PCV, the pistons would act as a pressure pump and start to blow out seals. With *inadequate* PCV this can happen too. Enter Forced Induction.

PROBLEM
TRD does not make any changes to the PCV routing. This means under boost, the MPCV will close the valve (from manifold pressure on top of the valve). The IPCV at the Tbody is closed, so now under boost, there is *no PCV* at all! Take a long enough run under boost with a closed valve, pressure builds in the crankcase and head, and seals start to seep oil. On my truck, the valve cover gasket, IPCV hose and the oil cap all are wisping oil (better there than at the rear main I suppose) from sustained crankcase pressure.

THE FIX
Cost me 22USD + 5 minutes
* New PCV valve and seal - Dealer 8USD
* 24in 3/8in trans/emission line - 3bucks
* 24in of 5/16 trans/emission line - 3bucks
* 1 set of vacuum caps - 3 bucks (you only need the 3/8)
* 1 5/16 vacuum T - 2bucks
* 4 hose clamps - 3 bucks

* R&R PCV valve (watch out the lower half of the seal wants to split and fall into the valve cover!)

* Install T fiiting with 3inches of 5/16 tubing between supercharger and hose to vacuum booster

* Install 3/8 vacuum cap over manifold runner port and use hose clammp

* Install 24inches of 3/8 tubing from PCV valve to T at vacuum booster clamp it down well onto 5/16 T (or get 2 x 5/16 to 1 x 3/8 T)

Have a beer, yer done.

Now, what happens is that during idle, the vacuum in the SC inlet chamber is low enough that the PCV valve ball drops, and the IPCV at the Tbody works as designed. When the SC is under boost, the prechamber (SC bypass valve closed) is under full vacuum, and the PCV valve will now be open under boost. This allows PCV function to be present during sustained forced induction engine load without crankcase pressure buildup.

HTH

Scott Justusson
94 FZJ 80 Supercharged
 
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Good info Scott. Do you realize that this may be the first post from you that no one will argue?:)
Just don't tell Rick I had 4/17:idea:

I'm still trying to figure out why TRD didn't do something about this in the kit. I'm also trying to figure out why the CARB isn't requiring this type of mod on any aftermarket system either. Properly operating PCV circuit is pretty key to emission cleanliness.

Scott J
 

Waggoner5

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With little vacuum, I would say the the potential blow by will take the path of least resistance. The booster being a sealed part would seem to be safe, but who knows.... My luck would have a booster acting as a catch can.
 
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With little vacuum, I would say the the potential blow by will take the path of least resistance. The booster being a sealed part would seem to be safe, but who knows.... My luck would have a booster acting as a catch can.

I agree, and this has been my experience. Dan, I also noted that the hard line to the brake booster is higher than the port it attaches to on the SC. This means any residual oil that may be present in the short piece of junction hose on car shutoff can't defy the laws of physics and travel 'up' to the brake booster.

The stinky oil smell is gone now, and the off throttle (from boost) coast is a lot smoother now that there isn't pressure in the PCV system to relieve on transition on boost > off boost.

HTH

Scott Justusson
 
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Pcv Reroute Pic

Here's a pic of the rerouted PCV valve feed. Notice the idle PCV hose oil wisp from too much pressure in the valve cover prior to mod.

HTH

Scott Justusson
PCV REROUTE.jpg
 
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How come your metal booster pipe is all bent up?

Skipped one of the steps, which was to put the anchor bolt on the PS of the motor for that pipe. By the time we were ready to do that, it was no longer easily accessible. One of the reasons Dan, on my SC install post, I said follow the TRD instructions to the letter.

:doh:

SJ
 

landtank

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I'm trying to understand this and because I'm not completely familiar with the SC install I'm a little confused.

My understanding is that the throttle body is moved from the intake plenum over to the intake side of the supercharger. Now on my 96 the PCV valve is plumbed into throttle body.

If this is the same on the pre 95s then there is no pressure on that line as it's pre compressor. And even if it was post compressor there still would be vacuum on that line do to the venturi effect of how it is plumbed into the throttle body.

For those who don't understand the venturi effect, you can pass compressed air over a hole and create vacuum within that hole proportional to the amount of air flow. This is a very common method of creating vacuum via compressed air from an air compressor.
 
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So why not just mimic the 95+ trucks and have the hose from the PCV valve go to the throttle body?

It has this already Rick. If you look at the pic I put up, on the PS of the valve cover is a direct 3/8 hose that goes from the valve cover to a port on the Tbody. There is no PCV valve there. The PCV valve is on the intake manifold itself, which means 1 of 2 things.

The IPCV that goes to the Tbody doesn't have the venturi effect you think
OR
It's just not big enough (hose/vacuum) under WOT

My own training on PCV systems is that you want vacuum all the time in the valve cover and pan. I can tell you that when I measured vacuum off the IPCV (the throttle body port), vacuum fell off that port quickly. Which I interpret to mean that pressure can now build in the valve cover and pan. Which would explain why Toyota put the PCV valve and line to the intake runners, allowing a different vacuum feed under higher rpm ranges.

I'm not familiar with the PCV routing of the OBDII trucks. I suspect that the PCV is NOT hooked up to the same tbody port as the pre OBDII trucks. Otherwise on an SC system, you would be using pressure to blow upward the PCV ball bearing to relieve pressure in the valve cover and pan. There can be no vacuum in the valve cover or pan that way.

Could it be that in the OBDII trucks the Tbody port of the PCV is hooked to the IM side of the Butterfly? Might be worthy of testing. And if that's the case, I see a problem because the vacuum in the 'prechamber' of the SC is low when the BPV is open - no PCV operation during off boost.

I know this, as soon as I rerouted my PCV as described, the oil smell was gone immediately, and on/off boost transitions were much smoother.

Scott Justusson
 

cruiserdan

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I have withheld additional comment because I wanted to visit with my friend at TRD to ask him why they chose to leave the PCV the way it was.


He stated that they left it alone because the PCV valve is basicly a one way check valve and they did not see a pressing reason to move it. I thought that they may have been concerned with venting all that stuff through the rotorpack and possibly leaving excess deposits over time. He further stated that they do not think that would be a problem at all. The main benefit I was thinking of is in the case where you have an edgy PCV valve that may not be closing completely under boost. In this case you would lose some boost pressure and also vent pressure into the crankcase. With the PCV inlet moved that becomes a moot point.
 
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I have withheld additional comment because I wanted to visit with my friend at TRD to ask him why they chose to leave the PCV the way it was.


He stated that they left it alone because the PCV valve is basicly a one way check valve and they did not see a pressing reason to move it. I thought that they may have been concerned with venting all that stuff through the rotorpack and possibly leaving excess deposits over time. He further stated that they do not think that would be a problem at all. The main benefit I was thinking of is in the case where you have an edgy PCV valve that may not be closing completely under boost. In this case you would lose some boost pressure and also vent pressure into the crankcase. With the PCV inlet moved that becomes a moot point.

My response would be curiousity Dan. As I have spent many hours driving in Romer's part of the country, I know going up route 70 and over Rabbit Ears, there are times when the SC boost is constant, in the 10's of minutes, even more. One way ck valves work, but 6 large pistons pumping away with no way of relieving pressure, don't need more than 30 seconds to get a measure of pressure in the crankcase. BTMT.

On a stock production turbo or supercharged application, there IS PCV present during boost, which is why I went after the mod on my truck. I have a LOT of firsthand experience with blown seals by bad or modded/deleted PCV systems in the audi turbos. When I smelled the familiar burnt dynosaurs coming from under the hood of my 80 after some high spirited boost runs, I knew exactly what the problem was.

I will also note that the design of the PCV valve in the 80 is not ideal to a boosted motor. I'm working on getting a stock turbo application that will plug and play. Toyota probably makes one.

For quick shots of boost pressure, I don't see a big deal with leaving the PCV circuit alone. But a few prolonged boosted runs can and will blow out oil seals. Once blown out, quick shots of boost pressure is all that one needs to see the seals are compromised.

I like having the dual purpose PCV in my 94. It's actually a pretty neat stock deal. However, when adding boost pressure, it lacks the proper practical application of PCV theory of vacuum in the crankcase always.

The nice thing about the mod I did, it's cheap, it's easy, and it makes a noticeable difference. And a SC makes what toyota put in, just inadequate.

Scott J
 

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