Pvc mod

[Unique96Camaro]

Why do people do this mod, what does it to, is it safe, and just whats the point. I dont get this mod one bit if you could help explain it to me and let me know if i should do it to my car or not. thanks

[techsan23]

Re: Pvc mod

Why do people do this mod, what does it to, is it safe, and just whats the point. I dont get this mod one bit if you could help explain it to me and let me know if i should do it to my car or not. thanks

The small hole inside the throttle body feeds fresh filtered air into the upper intake manifold at times to flush out the infamous oily air GT was describing that accumulates in the engine. If you go forced induction and do not plug this hole it can pressurize the inside of the engine. I have heard of people having their dipstick shoot out of the dipstick tube because of this. You will most likely begin to see antifreeze leaks from your intake manifold, and oil leaking from the valve covers. The oil vapors in the air are not compressible and can damage the piston rings and other internals. This is why alternative positive crankcase ventilation is recommended.
Heres what a catch can looks like; it separates the oil from the air:http://motors.shop.ebay.com/i.html?_...506.m270.l1313
And GT gave you a link that illustrates a few possibilities on how to plumb it in.

[FirebirdGT]

Re: Pvc mod

Why not to do it:

http://www.camaro5.com/forums/showthread.php?t=59340


How the PCV system is upgraded with an AOS:

http://www.ls1tech.com/forums/11059703-post70.html


This is the AOS I will be installing this spring.

http://www.conceptualpolymer.com/new_page_1.htm

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[Pewter02Camaro]

Re: Pvc mod

I understand the whole fresh air in bad air into engine to be burned. With that said our system when working proporly only produces a positive crankcase vacum and does not introduce fresh air into the crankcase. Unless ther is a fresh air path i've never noticed. So as long as you give it a way to "breath" after disabling it i dont get what the issue is. Also i did read the links that you posted. I guess my point is the factory setup does not do what a "catch can" setup does, it only creates vacum, and does not circulate fresh air in to the crank case.

[FirebirdGT]

Re: Pvc mod

I understand the whole fresh air in bad air into engine to be burned. With that said our system when working proporly only produces a positive crankcase vacum and does not introduce fresh air into the crankcase. So as long as you give it a way to "breath" after disabling it i dont get what the issue is. Also i did read the links that you posted. I guess my point is the factory setup does not do what a "catch can" setup does, it only creates vacum, and does not circulate fresh air in to the crank case.

Yes it does. The PCV system intake port is in the TB wall. (This is how you get oil in the TB.) Then out of the TB, through a passage in the UIM, through a hole in the LIM and into the crankcase. The vent is through another hole in the LIM into the "oil separator chamber" in the UIM, through the PCV valve and then through an internal passage in the UIM into the UIM plenum - where it mixes with the clean intake air, exhaust recirc and fuel tank vapors before entering the cylinders.

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[Pewter02Camaro]

Re: Pvc mod

It's not that i dont trust you but i've never seen any other holes on my '02's tb only the passage from the pcv itself. the only pcv passage i could ever fin was the one thaty comes from the passanger side head up through the LIM then into the UIM to the PCV itself then to the TB behing the MAF. Where is the fresh air inlet for the crankcase?

[FirebirdGT]

Re: Pvc mod

It's not that i dont trust you but i've never seen any other holes on my '02's tb only the passage from the pcv itself. the only pcv passage i could ever fin was the one thaty comes from the passanger side head up through the LIM then into the UIM to the PCV itself then to the TB behing the MAF. Where is the fresh air inlet for the crankcase?

Well it's there. Goes through the wall of the TB, through the TB and UIM flange, through the wall of the UIM into a chamber over a hole in the LIM.

I have the UIM and LIM on my work bench.
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[ssms5411]

Re: Pvc mod

I have had mine blocked since 02' and no problems an no catch can, just the valve cover breather.

[FirebirdGT]

Re: Pvc mod

I have had mine blocked since 02' and no problems an no catch can, just the valve cover breather.

The problem is not immediate, or short term, and you can't see the damage being done. Using a 1960's PCV system slowly detroys the engine internals.

I have 250K on this engine, and intend to do another 250K.

Yes, the engine will run fine - BUT it is unhealthy for the engine. I just won't do it, nor will I ever recommend anyone else to do it.
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[Pewter02Camaro]

Re: Pvc mod

I am going to have to disagree with this. If our pcv systyem used a cross flow setup simply plugging the TB pcv hole and running a breather would constitute a rather large vacum leak. Which it is obviously not the case.

[FirebirdGT]

Re: Pvc mod

I am going to have to disagree with this. If our pcv systyem used a cross flow setup simply plugging the TB pcv hole and running a breather would constitute a rather large vacum leak. Which it is obviously not the case.

Not sure what you are getting at here, BUT - the crankcase is PRESSURIZED [That's why 60's cars have oil all over the valve covers (from the breathers) and "smoke" after a hard run!], but it needs the intake manifold vacuum to "pull" the vapors out. [If you were driving cars in the 60s and 70s you would maybe understand better.] Didn't you read the article I posted? Well written and correct.
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[Pewter02Camaro]

Re: Pvc mod

Now on to today’s where it is a system that is closed for emissions. The gasses that are drawn through the crankcase into the intake manifold are burnt through the combustion process & then the catalytic converters. Filtered fresh air is drawn from the throttle body front or the intake coupler where it is filtered by the main air filter so no need for a secondary filter to get ignored & clogged. Then the fresh air enters the passenger side valve cover is pulled through the rockers, down the push rod valleys, through the heart of the crankcase where it flushes out all the harmful stuff mentioned earlier) , up the drivers side push rod valleys, through the drivers side rockers, out the rear of the drivers side valve cover, (or the valley cover on LS2/3/7) through the foam covered plastic hose around the rear of the motor, back up along the passenger side valve cover, to the PCV valve to the intake manifold & through the combustion process the amount of vacuum is regulated by the PCV valve. And a motor only pulls vacuum at an idle or low speed....at high RPM's the blow-by (yes, even the best motor has some) would push oil back into the intake if not for the checkvalve action of the PCV.

This is what I am refering to from the first link you posted. Again I say that if you plugged the TB PCV hole and added a breather you would be introducing a vacum leak into the system. Becasue the fresh air would in an oem setup be meterd before entering the pcv system.

Pic of PCV hole behind MAF on a drive by wire car. Disregard N2O jet.

Not sure what you are getting at here, BUT - the crankcase is PRESSURIZED [That's why 60's cars have oil all over the valve covers (from the breathers) and "smoke" after a hard run!], but it needs the intake manifold vacuum to "pull" the vapors out. [If you were driving cars in the 60s and 70s you would maybe understand better.] Didn't you read the article I posted? Well written and correct.
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I understand that blowby will always pressurize the crankcase. But the vapors will either be pushed out the breather by said pressure or be pulled out by manifold vacum. Either way air will be moving. Unless there is some sort of crossflow system, even if you have vacum pulling at the vapors you can never get fresh air to replace them inside the crankcase.

[FirebirdGT]

Re: Pvc mod

I think I see what you are getting at here - "the vapors will either be pushed out the breather by said pressure or be pulled out by manifold vacum" - so you are implying that the TB intake port serves no purpose as the "crankcase - PCV - UIM - cylinder - crankcase" is a closed system.

Point taken. When I install the AOS this summer, I'll install some pressure/vacuum gauges to get some quantitative data.

Regardless, do not disable the PCV system, but install an AOS to remove the suspended oil before it returns to the intake manifold.
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[Pewter02Camaro]

Re: Pvc mod

Basicly. Ideally you would still run a catch can setup and plumb it to in front of the turbo/supercharger to pull it into the motor and the system would still work as initially designed. Though a breather will still prevent vapor/pressure build up. I see the vapor recirulation portion as more of a EPA driven device.

[Pewter02Camaro]

Re: Pvc mod

Robert,

I think i've stumbled onto something here. This could be huge. Ok.
Went out to look at the car today after our discussion earlier. When i did the pcv mod. I pluged the system by filling my PCV valve with RTV. I now realise that this was wrong. By doing it this way i disabled the air passage that runs from the crankcase to the manifold. But this left the passage from the throttle body(behind the MAF) to the crank case open to the atmosphere via my breather. This in essance creates a vacum leak or in my case, the reason i built no boost on the dyno, a place for my boost to escape. I cant belive i didn't catch this before. Bottem line is I botched that one. And you were correct in quoting the link you gave that i posted a portion of above.

With that said here's where the rest comes in. Say you disable the PCV passage with a plug right at the throttle body and the vent the crankcase with a breahter. Because you still have a passage from the crankcase to the manifold present you still have a vacum leak. So as far as i can figure unless you plug both passages, the one that runs from the throttle body to the crankcase and the one that runs from the crankcase to the manifold you will have a vacum leak that may go unnoticed.

If you would be so kind since my top end is still assembled could you verify where the second passage is?