PCV 101 for Forced Induction 80's (1 Viewer)

[SUMOTOY]

I should clarify and state the he thought it would be fine to move it like you did, they just didn't want to bother with it. My original statement was not clear on that.

And I should clarify that doing nothing to the PCV circuit on a TRD equipped 80 has been known to work as well. I still believe that the way I ran it is the proper way to do a circuit on a boost system that's known to be under pressure for extended periods of time.

Thanks for cking tho dan, I believe the story.


Scott J

 

[landtank]

my understanding is that the Supra Turbos bring the PCV line over to the low side of the compressor. Wouldn't this be just the same as the current line at the Throttle body?

I still don't get the complexity of what you've done.

To me, simply capping off the PS nipple on the valve cover and the one at the intake plenum and then routing the PCV line over to the throttle body would do just fine.

 

[cruiserdan]

You would have to see one in the flesh. It's really not complicated.

 

[SUMOTOY]

my understanding is that the Supra Turbos bring the PCV line over to the low side of the compressor. Wouldn't this be just the same as the current line at the Throttle body?

I still don't get the complexity of what you've done.

To me, simply capping off the PS nipple on the valve cover and the one at the intake plenum and then routing the PCV line over to the throttle body would do just fine.

"complexity"?! Rick, I did this in the parking lot of my local Murrays Atuo. I had the following tools
Apple carving knife
1 pair of channel locks
Still only took my 5 minutes (less if I cut the short piece of 5/16 hose shorter the first time - cuz channel locks on hose clamps is a PITA)

I don't agree that capping off PCV is a good move here. First, what you describe is already on the truck (and on most stock turbo/SC cars), it's referred to as low idle PCV. The second line, with the valve, assures that under WOT vacuum (stock at the IM) or WOT boost (TRD SC at the SC inlet), there is enough vacuum to draw up the PCV valve ball.

If you really nerd on PCV systems for a while, you will understand that 'simplicity' is misleading. Too much vacuum at the wrong time, you suck raw oil, too little vacuum at the wrong time, you will follow with too much at the right time. With no PCV under extended boost, you can blow out engine seals regularly. One's best hope is that the rear main isn't one of the victims here.

I'm not sure I understand the confusion. NO PCV under sustained boost conditions can be a problem. Even the old CIS turbo cars uses dual PCV.

Here, it's almost silly NOT to do the mod on a boosted truck, there is no complexity, or downside to it.

And it's a 1 job. I wish it were more complicated!

Scott Justusson

 

[cruiserdan]

I wish it were more complicated!

Scott Justusson

It is when you can't find the "just right" brass do-hickey to make a nice sanitary T off of the adapter.

Places around here just don't have cool brass fittings like they used to. All I can find is the nylon crap...

 

[landtank]

"complexity"?! Rick, I did this in the parking lot of my local Murrays Atuo. I had the following tools
Apple carving knife
1 pair of channel locks
Still only took my 5 minutes (less if I cut the short piece of 5/16 hose shorter the first time - cuz channel locks on hose clamps is a PITA)

I don't agree that capping off PCV is a good move here. First, what you describe is already on the truck (and on most stock turbo/SC cars), it's referred to as low idle PCV. The second line, with the valve, assures that under WOT vacuum (stock at the IM) or WOT boost (TRD SC at the SC inlet), there is enough vacuum to draw up the PCV valve ball.

If you really nerd on PCV systems for a while, you will understand that 'simplicity' is misleading. Too much vacuum at the wrong time, you suck raw oil, too little vacuum at the wrong time, you will follow with too much at the right time. With no PCV under extended boost, you can blow out engine seals regularly. One's best hope is that the rear main isn't one of the victims here.

I'm not sure I understand the confusion. NO PCV under sustained boost conditions can be a problem. Even the old CIS turbo cars uses dual PCV.

Here, it's almost silly NOT to do the mod on a boosted truck, there is no complexity, or downside to it.

And it's a 1 job. I wish it were more complicated!

Scott Justusson

You're confusing complexity with difficulty. I didn't say it was difficult to do.

I'm puzzled why the brake booster needs to be part of the improved system.

I'll have to check out the Supra's factory setup more closely.

 

[cruiserdan]

The booster port on the throttle body adapter is the easiest place to get vacuum on the inlet side of the blower.

 

[Romer]

It is when you can't find the "just right" brass do-hickey to make a nice sanitary T off of the adapter.

Places around here just don't have cool brass fittings like they used to. All I can find is the nylon crap...

You ain't a kidding. All I could find for the subtank tee was plastic. I wasn't comfortable with plastic and after checking on line and driving around town today, I made the following brass T for my subtank. Wasn't cheap either.

 

[landtank]

I've done some research on how Toyota addresses this on their twin turbo Supras from the early 90s.

From what I can tell it's the same as a stock Land Cruiser setup.

NON boost situation:

there is vacuum in the intake chamber which pulls the ball up in the PCV valve. This draws air from the second line on the valve cover as well as any combustion gases present in the valve cover.

Boosted situation:

There is pressure in the intake chamber pushes the ball down and seals off the valve cover. Since the second line is open any pressure from blow by gases are vented through it to spot pre-compressor.

Since on the supercharger you move the throttle body to the intake side of the compressor than that second open line is on the low side and would function exactly the same as the Turbo Supra setup.

Now if you are Turbo'd then you need to move things around. This is because the throttle body is located post compressor. Both lines would be in a boosted situation and no venting would be possible until the pressure in the valve cover exceeded the amount of boost.

So on a Turbo'd truck that second line on the valve cover on the PS needs to be relocated to a spot pre-Turbo so when under boost gases can vent out it.

It seems to me that if you have weeping at the gaskets on a Supercharged engine you have a restriction in that second line hindering venting.

 

[SUMOTOY]

Rick:
The supra turbo PCV operates the same way I've seen every other production turbo PCV, including the audis. I don't disagree that the hookup you describe is how to run a turbo setup, but it's not necessary in a SC setup. When the SC bypass valve is closed, there is vacuum in the SC prechamber, the same as running the secondary PCV with valve pre turbo.

Rick, there is no clog in the primary line, I measured the vacuum at idle AT the valve cover. The booster has nothing to do with the routing, it was a handy source of vacuum, and I know that generally, booster vacuum sources are mounted where they see the most of it, even in boosted apps. What you are missing IMO, is that under high vacuum, that throttle body port is not effective at the job of PCV in a *stock* truck. Otherwise, there would be no second PCV with valve mounted in the intake manifold.

Put another way, in the stock truck the IPCV (throttle body) isn't sufficient for proper PCV operation, so a second PCV valve was installed directly into the intake manifold. Are you saying that with a boosted truck (second PCV closed under high rpm + boost) the throttle body PCV is now plenty?

Toyota disagrees with you on a stock truck! You are making this too complicated, and I would encourage you to consider exactly the difference between what I did with the SC PCV and what the supra turbo has. It seems to me, I've done exactly what the factory would do with a boosted engine. To wit: put the secondary PCV to a vacuum source under boost.

Scott Justusson
94 SC FZJ80 Supercharged and Sumotoy PCV

I've done some research on how Toyota addresses this on their twin turbo Supras from the early 90s.

From what I can tell it's the same as a stock Land Cruiser setup.

NON boost situation:

there is vacuum in the intake chamber which pulls the ball up in the PCV valve. This draws air from the second line on the valve cover as well as any combustion gases present in the valve cover.

Boosted situation:

There is pressure in the intake chamber pushes the ball down and seals off the valve cover. Since the second line is open any pressure from blow by gases are vented through it to spot pre-compressor.

Since on the supercharger you move the throttle body to the intake side of the compressor than that second open line is on the low side and would function exactly the same as the Turbo Supra setup.

Now if you are Turbo'd then you need to move things around. This is because the throttle body is located post compressor. Both lines would be in a boosted situation and no venting would be possible until the pressure in the valve cover exceeded the amount of boost.

So on a Turbo'd truck that second line on the valve cover on the PS needs to be relocated to a spot pre-Turbo so when under boost gases can vent out it.

It seems to me that if you have weeping at the gaskets on a Supercharged engine you have a restriction in that second line hindering venting.

 

[SUMOTOY]

It is when you can't find the "just right" brass do-hickey to make a nice sanitary T off of the adapter.

Places around here just don't have cool brass fittings like they used to. All I can find is the nylon crap...

Well, the nylon crap is in the elbow at the idle PCV Dan! And the nylon crap is found in most PCV systems anyhow. I spent 1.79 on the plastic T, and have run them for many years on other PCV systems over the years. Remember, it won't ever see boost, only mild vacuum anyhow.

Again, I encourage you guys to do the mod, not make it complicated. It's a simple fix, and I'd spend more money on the IM plug than I would on the vacuum T.

Scott J

 

[landtank]

I looked through TIS for my info and description of how the Supra system works.

That second line on the PS of the valve cover basically goes to a position pre turbo which is basically at atmosphere.

I'm not sure how I'm over complicating it.



And I have that same oily stain on my second line that you have and I'm only NA. What you are assuming is a problem might just be normal.

 

[SUMOTOY]

I looked through TIS for my info and description of how the Supra system works.

That second line on the PS of the valve cover basically goes to a position pre turbo which is basically at atmosphere.

I'm not sure how I'm over complicating it.

It's not at atmosphere, it's pre turbo, which means it's under vacuum *always*, more as the turbo gets up to speed. If there was no vacuum, you'd have pooling of oil at the entry point and upstream of it. Every turbo car I'm familiar with this dual type PCV system will show evidence that turbo compressor vacuum draws the venting into the turbo, which then blows it into the intake manifold.

And I have that same oily stain on my second line that you have and I'm only NA. What you are assuming is a problem might just be normal.

Could be. I also had it leaking from my oil cap and my valve cover gasket Rick. If you have that too, then your truck must stink as much as mine did before the relocation of the PCV.



Scott Justusson
'94 FZJ80 Supercharged and Sumotoy PCV mod

 

[cruiserdan]

Well, the nylon crap is in the elbow at the idle PCV Dan!

Um,

Not on mine.....

 

[landtank]

I can tell you that when I measured vacuum off the IPCV (the throttle body port), vacuum fell off that port quickly.

It's not at atmosphere, it's pre turbo, which means it's under vacuum *always*, more as the turbo gets up to speed.

Which is it?

 

[SUMOTOY]

Originally Posted by SUMOTOY
I can tell you that when I measured vacuum off the IPCV (the throttle body port), vacuum fell off that port quickly.


Quote:
Originally Posted by SUMOTOY
It's not at atmosphere, it's pre turbo, which means it's under vacuum *always*, more as the turbo gets up to speed.

which is it?

Hey Rick:
It's tough getting thru here, on a simple concept. The throttle body ports on the 80 are specifically designed to operate differently in terms of vacuum measured under different conditions. Try it yourself, measure the port at the Tbody, measure any of the other ports off the Tbody, they all have different characteristics/transitions. IOW, they aren't all just the same as an IM measure. 80's aren't unique with this concept.

Let's be clear: Which is it? It's both! Pre turbo IS AWAYS UNDER VACUUM. Throttle body depends on the port measured.

Please make your point, or call this mod good. If you are confused, I can try mapping the PCV circuit out more clearly than the pic. If you need help understanding PCV in a turbo project, please ask. If you can't understand the difference in the above quotes, then it might be better if you did some measures of the various T body ports yourself.


Scott Justusson

 

[landtank]

I can try mapping the PCV circuit out more clearly than the pic.
Scott Justusson

Thanks for taking the time to draw it out for me.


edit; it would help me to first understand how what Toyota did wrong before jumping into the solution.

 

[Romer]

Scott, nice thread. You described the situation, your defined problem and your solution well. The picture really helped. You explained at a level that most could follow.

I know it's based on a theory and your perception based on what you saw and I think it's great that you took action and provided your solution to the forum. Not everyone will agree, but that's what discussion is all about.

If you could continue to post your threads at this level of discussion, I think the forum would benifit from it.

 

[landtank]

You explained at a level that most could follow.

One thing to understand is that everyone learns things in different ways. Some can read text and answer questions all day long on what they read. Others like myself are visual or tactile learners.

This not to say I can't understand what I read but it typically needs to be in a familiar text and order that I'm accustomed to. But I do have a hard time with the way Scott writes.

 

[SUMOTOY]

This not to say I can't understand what I read but it typically needs to be in a familiar text and order that I'm accustomed to. But I do have a hard time with the way Scott writes.

Why I took pictures! I'd be happy to continue a discussion in PM on what you didn't understand about post 1.

It's not what Toyota did Rick, it's what TRD decided not to do. Which is to address PCV when adding boost. Your comparo to the supra turbo is a great reason to do what I did, they addressed PCV under boost, TRD didn't with the SC.

An easy change to the theory and application of the toyota turbo, and just about every other production turbo application, does with the PCV circuit. Those applications define the need, as did the stinky leaks from inadequate PCV on my truck. Swap the feed to a vacuum source, all is good and factory supported in theory and application.

HTH

Scott Justusson