Which PCV valve - 351W

Bob In Ct · #1 (**permalink**) 10-01-2002, 05:58 PM

I've got a 351W crate engine, dual plane, Holley 750 CFM. I've decided to install a PCV valve. When I go to the auto parts store there are 50 of them hanging on the hooks. Which one should I be using? I imagine that different valves flow different amounts of air. I would like to flow a lesser amont of crankcase air.

Any suggestions (brand, models)?

Thanks, Bob

xlr8or · #2 (**permalink**) 10-01-2002, 09:24 PM

Why run one at all?
Is there a specific reason you decided to use one?
Why not just vent it?

Mr.Fixit · #3 (**permalink**) 10-02-2002, 08:21 AM

Billit specialties sells a breather cap with a replaceable PCV valve in it. Looks good too.

scottj · #4 (**permalink**) 10-02-2002, 01:38 PM

Curious... why one that would limit venting?

SPF1116 · #5 (**permalink**) 10-02-2002, 02:56 PM

Let me take a stab at answering this.
1) I went to our local NAPA store and the counterman sold me a PCV valve for a 351W. He said it was for just about EVERY 351W. If you need, I can pop it out, read its number, and report back.
2) I too got a breather cap that the PCV valve fits in.
3) When I got my car, I was told that it would not require a PCV valve. But, within a few months, there was a fine layer of oil on top of both valve covers under the breathers. The PCV valve cures this and now the valve covers remain clean.

I hope this helps,
Steve

Mr.Fixit · #6 (**permalink**) 10-02-2002, 03:06 PM

If your breathers are dumping oil on the valve covers, a PCV is NOT the answer. All that will do for you is let your intake suck up that oil and have your motor burn it. You need better baffles in the valve covers to separate the oil mist from the "air" before letting it out. If yoy can't baffle the valve covers any better, there are breather stands available which have good baffling.

Bob In Ct · #7 (**permalink**) 10-02-2002, 03:36 PM

Right now it's just vented, with no problems. I feel the oil would be better off if there was some circulation of new air in the crankcase.

Bob

Mr.Fixit · #8 (**permalink**) 10-02-2002, 03:42 PM

Bob, I would advise you to leave things as they are. One good breather on each valve cover is all you ought to need.

Whaler · #9 (**permalink**) 10-02-2002, 04:26 PM

A little extra info on the topic

whaler

mr0077 · #10 (**permalink**) 10-02-2002, 06:50 PM

Good info, whaler...I would strongly recommend using a PCV valve for the engine protection it will provide...emissions are a plus. Some here say our motors never see that much "daily" type driving, so a PCV valve is unnecessary...I think if the jetting accounts for it, you're better off with one than without...just my dos centavos.

JAM1775 · #11 (**permalink**) 10-03-2002, 05:51 AM

Interesting article ..but I do not see where the PCV ensures engine protection over a properly vented crankcase. It helps with emmisions which is usually not an issue with our cars.
A clogged or dirty PCV, according to the article, can "cause" engine damage. ..oh..oh. I never noticed oil residue on my covers that could not be wiped clean with my regular maintenance. A vented crankcase is a must, whether it is vented with breathers on the covers, tubed down below or with a PCV. I prefer open breathers and nothing but a COOL/CLEAN air charge flowing down the carb.

scottj · #12 (**permalink**) 10-03-2002, 06:22 AM

Because piston rings don't seal 100% you have to have a place to vent the blow-bye. A PCV valve's size is determined by someone's best guess as to how much venting your engine needs to maintain normal pressure. Engine size and condition will change an engine's venting requirements, too much venting and you will get moisture in the oil, too little and you will get oil leaks and overloaded oil rings. PCV valves were developed because the government cares more about emissions than about the inside of your engine.

Scott

Jack21 · #13 (**permalink**) 10-03-2002, 04:56 PM

Bob in Ct.

If you have a race engine in a race car, you don't need a PCV. If you have a street engine in a street car, you need a PCV.

PCV (positive crankcase ventilation) valves have been installed on virtually all engines since about 1963. It puts the inside of your engine under a slight vacuum, removes the oil vapors generated in the crankcase from your engine, injects this under the carb base into the intake where the vapors are burned. And it only does this when the engine is under high vacuum or low load so it doesn't mess up your power enrichment.

There should be an air inlet breather on the drivers side valve cover. With the engine running, if you put your thumb over this hole with the breather out, you can feel the vacuum. The air then circulates through the engine to the passenger side valve cover where the PCV pulls the air and oil vapors out through a hose to the intake.

Go to the Fram or Purolator book alongside the rack of PCV valves, find the part number for a early - mid-70's PCV for a Ford 351W. If there are a couple to choose from, the one you want is the one with the little plastic 90 deg elbow on top with a 3/8" hose fitting.

Remember to jet your carb primaries about 2 steps richer to make up for the extra air the PCV lets in. Secondaries shouldn't be affected.

Can you get by without one? Sure. But your engine, and engine compartment will get dirtier (oilier) faster.

flipper35 · #14 (**permalink**) 10-03-2002, 05:47 PM

I would ask your engine builder how much you can drop the octane. Oil vapor sucked in and burned can make your octane rating drop from 92 to 88-89. I vent my engine, properly baffled there is very little oil to wipe off and here in the desert I don't worry about condensation much. PCVs are better for emmisions.