Holley carb & PCV location ?
Thread Starter
Le Mans Master
Joined: Apr 2000
Posts: 7,562
Likes: 9
From: B'Ville NY
Cruise-In III Veteran
St. Jude Donor '05
Holley carb & PCV location ?
I'm curious where people are connecting their PCV valves when using square bore Holleys?
I have a drop base air cleaner on top of my carb with a rubber hose going from the PCV to the underside of the cleaner base. The reason I'm asking is that I get some oil out of the breather in the valve cover and I'm wonder if I'm not getting enough crankcase vacuum :confused: . I didn't install it in a "T" fitting at the back bottom of the Holley becasue I didn't know if it'd affect my lights.
The engine was rebuilt 5 years ago (including new pistons & rings) and probably has about 6000 miles on it since.
TIA :cheers:
I have a drop base air cleaner on top of my carb with a rubber hose going from the PCV to the underside of the cleaner base. The reason I'm asking is that I get some oil out of the breather in the valve cover and I'm wonder if I'm not getting enough crankcase vacuum :confused: . I didn't install it in a "T" fitting at the back bottom of the Holley becasue I didn't know if it'd affect my lights.
The engine was rebuilt 5 years ago (including new pistons & rings) and probably has about 6000 miles on it since.
TIA :cheers:
Safety Car
Joined: Feb 1999
Posts: 3,631
Likes: 14
From: Fountain Hills AZ
Re: Holley carb & PCV location ? (SmokedTires)
The pcv valve needs to be connected to vacuum or else it doesn't function. The fitting on the air cleaner base is intended to provide clean air into the crankcase to replace the air being drawn out through the pcv valve. It sounds like you have a breather on the valve cover, which does the same thing as the air cleaner fitting is supposed to do (vent the crankcase). There are several ways to vent your crankcase but if you want a functional pcv system you need to connect the valve to vacuum, either at the carb or the manifold. As it is now, it sounds like your crankcase is breathing and exhaling entirely through the valve cover breather and the pcv is not providing any vacuum to your crankcase.
Some oil out of a breather is normal as the air coming out of the crankcase will carry a "mist" of oil. In a factory type sealed system, that air/mist goes into the air cleaner to be reburned and isn't noticed unless there's too much blowby. If you only have one breather and no functional pcv, positive pressure can also force raw oil into the breather and through it's grommet also. In most cases, the sealed factory type system is the best as it provides both vacuum and also "recycles" the oil mist through combustion rather than gunking up the outside of the engine.
Some oil out of a breather is normal as the air coming out of the crankcase will carry a "mist" of oil. In a factory type sealed system, that air/mist goes into the air cleaner to be reburned and isn't noticed unless there's too much blowby. If you only have one breather and no functional pcv, positive pressure can also force raw oil into the breather and through it's grommet also. In most cases, the sealed factory type system is the best as it provides both vacuum and also "recycles" the oil mist through combustion rather than gunking up the outside of the engine.
Thread Starter
Le Mans Master
Joined: Apr 2000
Posts: 7,562
Likes: 9
From: B'Ville NY
Cruise-In III Veteran
St. Jude Donor '05
Re: Holley carb & PCV location ? (Vetterodder)
Thanks Vetterodder, I never even thought of looking at the intake manifold to port to. This does explain things for me though :) .
Advanced
Joined: May 2002
Posts: 63
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From: Wylie TX
Re: Holley carb & PCV location ? (SmokedTires)
I am looking at a similiar problem with the vaccuum ports on my Holley carb. There is not enough ports to feed everything. I need to connect to the lights, brakes, distributor, pcv, etc and only have three ports. The only place on my manifold (vortec performer RPM ) is covered by the carb (holley 4160) Not sure what to do here. Any suggestions??
Le Mans Master
Joined: Oct 2002
Posts: 5,714
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From: Silver City NM
St. Jude Donor '05-'07
Re: Holley carb & PCV location ? (SmokedTires)
There are adapter plates that fit under Holley carbs and have a vacuum tube sticking out of them. It may raise your carb 1/4-1/2 inch but it will provide a source for vacuum. Not sure if I saw them in Jegs or Summit.
Race Director
Joined: Mar 2001
Posts: 11,322
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From: Living in the Hartland
Re: Holley carb & PCV location ? (tim_briz)
Your lights , brakes and acc should be hooked to a port on the manifold itself while the pcv is hooked directly to the carb. The manifold hook up has a special connector that goes inline and acts as a one way valve while the pcv has a check ball that only draws when the carb is drawing vac above the pcv's rating. I believe the pcv connect lets the littel bit of oil it sucks to be burnt with the intake charge. Get a vac diagram for your year and it will have all this in detail.
Hope this helps.
Hope this helps.
