PCV delete, vent to atmosphere, oil fumes when driving and engine braking.

[McGruber21]

My 280z has an AZ zcar 4 barrel Holley carb manifold on it and I have deleted the PCV, that would normally vent back into the stock EFI manifold, with just a filter venting to atmosphere. The engine runs great and pulls hard but I've noticed oil fumes while Im driving and engine braking, now I have no engine oil leaks and my engine doesn't burn oil, so i have isolated the smell to the air filter that Ive attached to the Crankcase vent tubing on the side of the engine(shown in pictures). My question is, can I run any inline PCV valve with a rubber hose running down toward the underside of the car with an air filter on the end? or does the PCV need vacuum? I know I'm losing some power by venting straight to atmosphere, I understand that vacuum in the crankcase can increase horsepower in some instances, but I mainly want to fix the oil smell. Thanks.

[NewZed]

You could block that lower hose and run a hose from the valve cover to the air filter, like AZC describes.

 

http://www.arizonazcar.com/cableinstall.html

[McGruber21]

You could block that lower hose and run a hose from the valve cover to the air filter, like AZC describes.

 

http://www.arizonazcar.com/cableinstall.html

Thanks for the response, I have the valve cover connected to the air filter on the carb like AZC describes. I thought about blocking the lower hose but feared that blocking the lower hose could create problems? The crankcase should have a PCV type system like a vent or vacuum.

[Chickenman]

You do not want to block the lower hose period. Put an operating PCV back in the system. The 4 barrel manifold or your Holley carb itself should have a fitting for the PCV valve. Hopefully they have added a port to thread the factory PCV valve in to the Intake manifold. If you have that, then attach the PCV hose to that. You can get brass barbed hose connectors that enable you to lengthen the factory lower PCV hose to reach to a new location. 1/2" to 3/8" is a common size, but lots of sizes are available. 

 

 

If your manifold is not drilled and threaded for the factory Nissan PCV valve, then there should be a 3/8" diameter tube port at the bottom rear or front of the Holley 4 barrel. Connect a PCV valve to that. You will have to buy a Chevy PCV valve. The 3/8"  tube end on the Chevy PCV valve goes to the carb side. The other end ( about 1/2" diameter ) you connect to the lower PCV hose.

 

Note: The AZ manifold does have a port on the front side of the manifold that could be used for the PCV valve. It can be re-tapped if the thread size is not correct. It may lean #1 and #2 cylinders out a little though. The Holley carb PCV tube gives an even distribution of PCV flow.

 

Connect the upper hose to the base of the Air cleaner as described by the AZ article. . Venting the lower hose or worse, blocking it is entirely wrong. I'm surprsied that AZ even suggested that. 

 

There are many advantages to running a properly functioning PCV system on a street vehicle and no disadvantages.

 

Here is an excellent article on Crankcase Ventilation Systems by Arrington Performance:

 

http://www.shophemi.com/images/media/p-2273-arrington_ccv_bible.pdf

Edited May 26, 2017 by Chickenman

[Chickenman]

Picture of Holley PCV tube. Any street Holley ( and some Race models ) will have this Tube. It can also be used as a brake booster connection:

 

[NewZed]

You can block the lower hose.  It will just be a 60's style crankcase vent.  Blowby will get sucked in to the engine and burned instead of sucked in to your nose.  Blocking the lower hose will be one level better than what you have now, but not as good as full "positive": vent system.

 

If you read down to the bottom of the AZC link he describes blocking the lower hose.

[McGruber21]

Picture of Holley PCV tube. Any street Holley ( and some Race models ) will have this Tube. It can also be used as a brake booster connection:

 

 

 

 

You can block the lower hose.  It will just be a 60's style crankcase vent.  Blowby will get sucked in to the engine and burned instead of sucked in to your nose.  Blocking the lower hose will be one level better than what you have now, but not as good as full "positive": vent system.

 

If you read down to the bottom of the AZC link he describes blocking the lower hose.

Thanks for the help, should I connect the vent tube to the carb fitting? with or with out a PCV valve?

[beermanpete]

If you use a fitting on the carb or manifold you need the PCV, otherwise you will create a massive vacuum leak.

 

I agree with Chickenman, replace the PCV. Do not simply block the crankcase block vent. If you do not reinstall a PCV you should run a hose down under the engine and positon the end to be in the air flow while driving and cut an angle on the back side so the front is the low edge. This will cause a draft to pull air in through the cracnkcase, entering at the vent on the valve cover and exiting at the tube below the engine. This will take water vapor and other gasses out of the crankcase. This is called a road draft tube and was common prior the adoptio of the PVC system in the mid-sixties.

[NewZed]

In theory the hose to the filter should provide a slight vacuum, pulling air through the filter you have on the lower hose, through the crankcase, and in to the air filter housing and engine.  

 

The road draft system that's described would really just reverse the flow direction of the blowby gases.  If you have lots of blowby you'll probably still get the smell.  And if you have lots of blowby, blocking the lower hose would probably oil up your filter.

 

So, you could block it like AZC says and all of the smell would probably be be consumed but there might be new problems.  There is no "period" for any of the possible ways you could go, or "entirely wrong".  And there are a variety of reasons to do any of them from saving the environment to saving your oil, and levels of difficulty, from simple to complicated.  

 

Best to just read up on PCV systems and choose a method.  You could block the lower hose while you're reading.

[BJSZED]

Been down this road. You will be lean on one side of the intake if you hook the pcv up to one side of the intake....better to use the PCV port on the carb or drill and thread in the center of the plenum divider to equal out distribution.

I would use the original pcv valve as it will flow the proper amounts.

[Chickenman]

Delete Post

Edited May 27, 2017 by Chickenman

[McGruber21]

Been down this road. You will be lean on one side of the intake if you hook the pcv up to one side of the intake....better to use the PCV port on the carb or drill and thread in the center of the plenum divider to equal out distribution.

I would use the original pcv valve as it will flow the proper amounts.

Thank you, I did something similar with good results, no oil smell. Thanks to everyone who helped.

[ozconnection]

An old thread, perhaps a new vision. 

 

The factory Nissan PCV valve flows enough air to change the idle afr's by two whole numbers on my innovate wb.

 

This is too much "un-metered" air entering into the intake manifold.

 

I added an appropriately sized ball valve to reduce but not completely stop the flow of these gasses back into the intake manifold. 

 

You'll be surprised how little opening there is on the valve , that it still evacuates the engine of blowby gasses and what effect it has on the idle on my L26.

 

Now, at idle, the Holley has its throttle plate correctly orientated with the transfer slot whereas before, the throttle was so closed, the transfer slot wasn't exposed. Previously the off idle characteristics were all wrong and it was hard to tune and drive at this point.

 

The engine now bursts to life with just a flick from the starter motor.

 

Almost all of the flow into the intake manifold is now through the carburetor, with just a whisk from the PCV. This little modification is like night and day for my engine, perhaps you could try it on yours if you're having idle/off idle tuning issues.

[McGruber21]

I've since converted to Triple Webers, but your approach would be the best fix.