I was thinking about this last night.

PCV valves are tuned to a particular engine, via internal check springs, right?

Those springs are matched to the manifold vacuum that the engine generates at idle, part throttle cruise, and heavy load/WOT. So, when someone changes the camshaft to something significantly more radical, wouldn't they have to change the PCV valve to match?

If I'm running an L98 PCV valve (L98's have puny little cams), on my ZZ4 (has about 15° more duration than L98), do I have worry about the PCV valve?

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Pro-Touring 71

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An easy test is to remove the valve and plug the line. If the engine runs better than the valve is causing too much air to enter, if the engine runs the same or alittle worse then the valve is ok. You have efi so you would proabably have to look at the fuel short term block learn and see if it is trimming more or less fuel.

Generally, no. They're all fairly similar, beleive it or not. Some leak a little more air, some a little less but it's always such a small amount that it doesn't make much difference.

The springs inside them are also fairly similar, although you would think they vary wildly. Unless you're pulling mid-single digit idle vacuum you'll have enough to keep the plunger retracted.

If you find that yours "flutters" a little at idle after you do the cam swap, or for any reason, try putting in a PCV for a 1991 Camaro 3.1L V6. Don't know exactly what is different about them. They work functionally the same but have less of a tendency to flutter than any V8 unit I have tried.

Ive been wondering about this mine acts like i have a vaccume leak if i hook it up?

It is a vacuum leak! A contolled one, but a leak none the less -

<font face="Arial,Verdana" size="2">Originally posted by Damon:

If you find that yours "flutters" a little at idle after you do the cam swap, or for any reason, try putting in a PCV for a 1991 Camaro 3.1L V6. Don't know exactly what is different about them. They work functionally the same but have less of a tendency to flutter than any V8 unit I have tried.</font>

That's interesting that you'd say that. My father-in-law (used to own a gas station/garage) said the exact same thing last night- "try a 3.1L V6 valve." He said it may work better with a lower vacuum (than stock) V8.

Hmmm, I'll give it a shot.


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Pro-Touring 71

1996 LT4 Corvette Wheels are 17x8.5 front, 17x9.5 rear
Wheel adapters are 2.0" front, 2.5" rear
Baer Brakes four wheel discs
Fuel Injected ZZ4, custom burned EPROM, AFR heads, TPIS Mini-Ram intake,
Comp Camshaft, TH700R4 Transmission.
God Bless the USA
Project Photos on ULTM8Z project photo album (http://photos.yahoo.com/ultm8z)
See me in Chevy High Performance (http://chevyhiperformance.com/featuredvehicles/86018/)
ULTM8Z Website (http://www.ultm8z.com)

Try a NEW DESIGN PCV valve for a '00 Chevy Silverado. Some of these new Vortec V8's experienced mysterious oil consumption. GM traced down to the PCV valve. The new design has no spring OR plunger. It is hollow. It looks like any other EXCEPT for the bottom has a tiny hole that regulates the vaccum pull on the crankcase. I'm not sure if the parts stores have these yet, but the dealerships do. My shop has a reliable source also. They will work on our cars also, I have one in both my 2nd Gens. Works perfectly fine.

What is the purpose of the pcv check valve? I'm guessing it is to prevent a backfire from spreading into the motor.

Also, is it really necessary to run one? As mentioned above, it is basically a vacuum leak often with with oil vapor that could affect the air/fuel mixture. Why not just run breathers on each valve cover?

If it is a good idea to run a pcv valve, is it better to plug the hole on the opposite valve cover or run a breather?

Ventilates crancase pressure (blow-by)

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The check valve isn't really a check valve at all. It's like a switch that goes between "tiny vacuum leak" and "high flow." Whenever there is meaningful engine vacuum (more than about 3-4" like when idling or at moderate throttle) it's a very small vacuum leak. When manifold vacuum drops down to basically zero (WOT) the valve opens up and allows a lot more flow. This is to help keep good airflow through the crankcase at WOT where there isn't much vacuum to help pull it through. They make up for the lack of vacuum by allowing the valve to flow a lot more.

To answer the follow-up question..... NO, this increased airflow through the PCV at WOT won't mess up your A/F ratio. It's a lot more airflow than when closed but it's still just a tiny percentage of the total airflow going into the engine. Too small to make any meaningful difference.

You can check this out for yourself by blowing through a PCV valve while using a small screwdriver to push the plunger in and out. When it's fully seated you'll be able to blow only a small amount of air through it. When you let it off the seat you can empty your lungs through it as fast as you can exhale.