[Scott Stoneburg]

Putting a mild 400 back together and I'm going to replace the PCV valve. From what i understand of their operation they open at a certain vacuum level to allow for crankcase pressure to vent to the intake. So my question is wouldnt the PCV valve for a mildly camed 400 be a different valve for a smog era 400 like a '77 Grand Prix? I looked them up at the Auto Parts website and list the same valve for a RA IV 400 & a '77 400. Am I missing something?

[Chief of the 60's]

I never had an issue using an average run of the mill, over the counter PCV valve and have done so on 600+ horse engines.

But if spending money makes you feel better try this > http://mewagner.com/?p=444

[Tom Vaught]

The valve does not care about the application very much as the valve is a variable valve that flows from 2.5 cfm to 4.5 cfm on 99% of the applications be it a Ford, Chevy, Chrysler, or Pontiac. The listing is correct. The final HP numbers mean nothing.

The mewagner valve is just another example of "I got your money" yet my valve is prettier vs your factory valve. But they do not tell you the function exactly the same way without all of the pieces to play with and screw up.

Tom V.

I have posted a list of a lot of available Ford PCV valves with the proper specs in the past. But spend your money however you wish. "A Fool and his Money are quickly parted" an old saying that is still true many years later vs the 1960s & 70s. Corporate Engineers would have been fired if they proposed a valve like the one mentioned above.

[Scott Stoneburg]

I'm definetly not lokking to spend money needlessly, just asking a question. I havent had a PCV valve in use in one of my motors for 30 years.

[Chief of the 60's]

Originally Posted by Scott Stoneburg

I'm definetly not lokking to spend money needlessly, just asking a question. I havent had a PCV valve in use in one of my motors for 30 years.

I don't like using them either (power loss) but when you have to please Johnny Law, sometimes you gotta do what you gotta do.

[Tom Vaught]

I tend to make decisions based on mathematics vs seat of the pants or JDKWTATA.

Typical Pontiac 4 bbl carb cfm (flow) 750

Typical OEM PCV Valve flow = 4 cfm

4 cfm divided by 750 cfm = .005333 percent change in power.

366 hp (GTO) times .005333 = 1.952 horsepower vs running without a PCV Valve.

So I agree there is a very slight change in the engines power production, but the
corrosive gases removed in the crankcase by the PCV valve is worth many times more benefit to the engine vs that 2 HP change. At least run some PCV Valve in the engine or the life of the engine decreases a lot. Henry Ford and others figured out that deal which is why road draft tubes were installed on engines prior to PCV Systems.

Tom V.

[Schurkey]

The engine doesn't know if the air is coming in from the PCV or from the carb venturi.

If the overall air/fuel mix is correct, it's correct. No power loss at all.

[coonhunter70]

They help keep the inside of an engine clean.

[Tom Vaught]

Originally Posted by Schurkey

The engine doesn't know if the air is coming in from the PCV or from the carb venturi.

If the overall air/fuel mix is correct, it's correct. No power loss at all.

The corrosive gases from the combustion process either go out the tailpipes or past the cylinder rings and down into the crankcase (oil pan).

Very few street engines have perfect sealing around the rings to the cylinder walls and between the pistons and the rings. Combustion gases go to the oil pan. Leave those gases in the pan and parts exposed to that gases deteriorate over time.

Tom V.

Lots of threads on the PCV system. Most are accurate as far as the actual
issues with not running a road draft tube or pcv system.

["QUICK-SILVER"]

Originally Posted by Tom Vaught

I tend to make decisions based on mathematics vs seat of the pants or JDKWTATA.

Typical Pontiac 4 bbl carb cfm (flow) 750

Typical OEM PCV Valve flow = 4 cfm

4 cfm divided by 750 cfm = .005333 percent change in power.

366 hp (GTO) times .005333 = 1.952 horsepower vs running without a PCV Valve.

So I agree there is a very slight change in the engines power production, but the
corrosive gases removed in the crankcase by the PCV valve is worth many times more benefit to the engine vs that 2 HP change. At least run some PCV Valve in the engine or the life of the engine decreases a lot. Henry Ford and others figured out that deal which is why road draft tubes were installed on engines prior to PCV Systems.

Tom V.

Tom,

Doesn't your math indicate high intake vacuum, at peak HP, to have 4 cfm going through the PCV?

Just askin'
Clay

[Tom Vaught]

The PCV Valve has a shuttle valve and spring inside of it.

The spring and shuttle valve position determine the PCV Valve flow past the valve and into the engine for different modes of driving.

So you cannot assume that at WOT you have one flow and at idle you have a different flow. The combustion gases maximum "leak" past the rings and into the oil pan area is not necessarily at a point you assume either.

In most cases with closed crankcase (no open breathers) at high rpm points the PCV valve does not flow enough to remove the higher crankcase pressures and the "PUSH" side of the system: (Valve cover, hose to aircleaner, and internal filter ) allow the excess pressure and gases to be mixed with the incoming air thru the filter and be burned by the engine. So the PCV valve does very little in a WOT situation.

Tom V.