PCV system in turbo engines - 3000GT/Stealth International Message Center

eyeluvmy3kgt · 09-22-2005, 01:49 AM

I know I "need" a catch can or Krank Vents for my PCV system but before going out and spending a couple hundred bones on those items I want to understand and possibly find a better way of venting the crankcase and keeping oil out of my intake.

FYI- when i refer to the "intake hose" I mean the hoses that go from the air filter to the turbos.

This is how I understand the basic idea of the PCV system in most modern engines-

1. The intent is to use the vacuum of the engine to help pull vapor buildup out of the crankcase.
2. There are 2 breather hoses connected to the intake, one at some point on each side of the throttle body.
3. The hose on the intake manifold side is a vacuum source which utilizes a PCV valve to keep positive pressure (boost) from entering the crankcase.
4. The other hose is also a vacuum source that connects to the intake hose before the throttle body, and in our case, before the turbos.

When the engine is in vacuum the breather hose on the intake hose side passes fresh air through the valve covers which mixes with the gas vapors and is sucked through the pcv valve into the intake manifold then burnt in the combustion.

Now, in a turbocharged engine, in boost, the pcv valve shuts. The gas vapors (and some oil) are sucked through the vacuum from the breather hose going to the intake between the air filter and the turbo.

OK, after anaylyzing all this to death, I don't see why we can't eliminate the pcv valve, plug the hole in the manifold, and vent both valve covers to the intake pipes, in front of the turbos. Wouldn't that be just as good of a ventillation for the crankcase? During boost you'd get just as much ventillation, maybe more from having 2 breather hoses instead of one connected to the intake hose.

Of course you'd still need to use a catch can.

Pros: no more pcv valves to go bad. no more gas/oil vapors going thru the pcv valve into the intake manifold. impossible to leak boost thru the pcv valve if it's not there.

Cons: you tell me

doctorstupid · 09-22-2005, 01:56 AM

Cons:
No crankcase vacuum
Won't pass emissions

That's about it. Doing what you outlined above has been done. Others pursue constant crankcase vacuum (which you won't get from the pre turbo intake, at least not any appreciable amount) with external vacuum pumps.

There's a relaly long thread around here in the Adv. Tech forum about this.

09-22-2005, 01:49 AM	#1 (permalink)
eyeluvmy3kgt 18 year old VR4 Join Date: Aug 2002 Location: Little Rock, AR Drives: '91 VR4, '08 Fit Trader Rating: (15)	PCV system in turbo engines I know I "need" a catch can or Krank Vents for my PCV system but before going out and spending a couple hundred bones on those items I want to understand and possibly find a better way of venting the crankcase and keeping oil out of my intake. FYI- when i refer to the "intake hose" I mean the hoses that go from the air filter to the turbos. This is how I understand the basic idea of the PCV system in most modern engines- 1. The intent is to use the vacuum of the engine to help pull vapor buildup out of the crankcase. 2. There are 2 breather hoses connected to the intake, one at some point on each side of the throttle body. 3. The hose on the intake manifold side is a vacuum source which utilizes a PCV valve to keep positive pressure (boost) from entering the crankcase. 4. The other hose is also a vacuum source that connects to the intake hose before the throttle body, and in our case, before the turbos. When the engine is in vacuum the breather hose on the intake hose side passes fresh air through the valve covers which mixes with the gas vapors and is sucked through the pcv valve into the intake manifold then burnt in the combustion. Now, in a turbocharged engine, in boost, the pcv valve shuts. The gas vapors (and some oil) are sucked through the vacuum from the breather hose going to the intake between the air filter and the turbo. OK, after anaylyzing all this to death, I don't see why we can't eliminate the pcv valve, plug the hole in the manifold, and vent both valve covers to the intake pipes, in front of the turbos. Wouldn't that be just as good of a ventillation for the crankcase? During boost you'd get just as much ventillation, maybe more from having 2 breather hoses instead of one connected to the intake hose. Of course you'd still need to use a catch can. Pros: no more pcv valves to go bad. no more gas/oil vapors going thru the pcv valve into the intake manifold. impossible to leak boost thru the pcv valve if it's not there. Cons: you tell me __________________ -Marshall 2nd Place "Best 1st gen" category '08 NG Car Show Check out My Pics and "The Story of My Car" UPDATED 6/22/08 with engine rebuild Engine rebuild: Done! 8/07 Paint: Done! 11/07

09-22-2005, 01:56 AM	#2 (permalink)
doctorstupid Banned from Classifieds Join Date: Sep 2003 Location: Lafayette, CO Drives: 3100GT VR-4 Trader Rating: (37)	Re: PCV system in turbo engines Cons: No crankcase vacuum Won't pass emissions That's about it. Doing what you outlined above has been done. Others pursue constant crankcase vacuum (which you won't get from the pre turbo intake, at least not any appreciable amount) with external vacuum pumps. There's a relaly long thread around here in the Adv. Tech forum about this.

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