herwawan

I know there's been a few threads about this topic but never a final resolution - this is an attempt to get the final word on what to do with aftermarket valve covers and PCV systems.

Most (if not all) aftermarket valve covers feature a simple fitting of the same size (most of them 3/8, some of them 1/4) on both sides to connect the OEM PCV system. Some of these aftermarket manufacturers are recommending using a PCV valve with their valve covers if the ones they replace have one integrated. Below is an example with Holley's valve covers:



That's when it becomes tricky. I've talked to a few manufacturers to see if there's a consensus on the topic... and there's not:
- some believe that the internal baffles on the covers do the restriction work
- others believe a PCV valve should be used

To understand the way the PCV system works on an LS7, I went to the service manual, and here is how it's described:

To be a little more specific when it comes to detail:
- the vent on the valley port is restricted (2.5 mm fixed orifice)
- the vent on the driver-side valve cover is also restricted (same 2.5 mm fixed orifice)
- the vent on the passenger-side cover doesn't seem to be restricted

And to make sure we all visualize what we're talking about, here is a diagram of the system.



So with all that in mind, basically the main difference between the OEM valve covers and aftermarket valve covers lies in the driver-side fitting:
- restricted (2.5mm fixed hole) with the OEM valve covers
- unrestricted with aftermarket valve covers

Now with all that in mind, should we add a PCV valve on the driver's side when installing aftermarket valve covers, or is it fine as it is? Curious to hear some feedback on that - I'm definitely not qualified to answer the question, but I'd really like to know (and I'm sure it can help a lot of other people).

Kingtal0n

The 2.5mm restrictor fitting is inside the valley cover, not needed in the valve covers. You can add a PCV valve between the 2.5mm valley cover orifice and the intake manifold if you want but it isn't necessary in natural aspirated applications since the PCV valve orifice blows wide open at WOT anyways. Thus the restrictor fitting sizes to simulate a pcv valve orifice at WOT.

The 'clean side' is where it connects valve cover to the throttle valve, this side utilizes pressure drop between the air filter and throttle valve to draw blow-by gas from the crankcase at WOT. It should be free flowing, This side never uses a PCV valve. You don't need a restrictor fitting here unless targeting a specific pressure drop for idle/cruise situation, which is sometimes done but unnecessary. Blow-by gas at WOT enters crankcase from piston-ring regions and is pulled from the crankcase through the valve cover into the engine throttle valve region between the air filter and throttle valve. During cruise/idle the condition is reversed, blow-by gas is pulled through valley cover 2.5mm fitting into intake manifold and fresh air enters the crankcase via valve cover 'clean side' which is why its the clean side, it takes filtered air from the air filter and lets that flow into the crankcase. The most important aspect of using this type of OEM pcv setup is to utilize a high quality air filter, this will protect the engine and crankcase from airbourne debris. The second most important aspect is to measure crankcase pressure and ensure it can maintain a reasonable pressure drop of 1" to 3" Hg at wide open throttle due to pressure drop supplied by air filter.

So answer your question no you don't need to worry about restricting the clean side valve covers. But I would measure crankcase pressure, use a quality air filter, and add a quality PCV valve between valley and intake manifold if you wanted, Use the Toyota Supra 95-98 Twin turbo Pcv valve IMO. CHevrolet seem to leak so much they are basically useless for high quality engines as the late model LS in performance apps.

ClothSeats

You seem to indicate that the driver side valve cover has a 2.5mm orifice, but the passenger side does not. That is not true. There is only one 2.5mm orifice in the whole system, and it is located in the connection at the valley cover.

Kingtal0n

It is curious to me that they restricted one of the valve covers, if this is true, There are only two reasons I can see to do this. One is to force the pcv system to breath mostly from the passenger side valve cover at cruise/idle which facilitates a singular, specific direction for crankcase gas to flow. It's not such a bad idea. This would also enhance the pressure signal applied to that specific passenger side valve cover, making PCV action more effective on that side of the engine. You may wish to include some kind of restrictor for the new driver side valve cover to simulate this effect. It shouldn't hurt to run without one but the more I think about it the more I like the idea. I wouldn't use a PCV valve though- just a small restrictor orifice is fine.

The other reason is if the driver's side valve cover has very little baffling inside, it may facilitate oil aspiration if the flow becomes significant on that side.

As the gentleman above suggests it is unlikely that there is an orifice in the driver side valve cover anyways. It would be strange, but, I've seen all kinds of OEM mods to account for PCV flow direction, kinetic energy, velocity, and so forth, to improve the PCV action for various conditions. You may find when measuring crankcase pressure that indeed a restrictor placed precariously will improve PCV action for cruise conditions. Lower crankcase pressure = improved engine oil quality.

herwawan

@Kingtal0n Currently, I use a MightyMouse Mild catch can so I’m already set up properly from the valley cover. My question was more specifically on the valve covers and you do bring some clarity to it. How can I measure the crankcase pressure? Does the ECM measures that somehow? I’d be curious to monitor that.




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This is what I see when looking inside the fitting on the driver-side valve cover. Do I read this wrong? Looks like a restrictor to me.

Kingtal0n

Supply a 1-bar map sensor with 5v and ground from a source other than the vehicle. Attach it somewhere inline close to the crankcase just off one of the valve covers where there is no PCV valve.

Record the 1-bar sensor voltage with engine off, baseline barometric volts. for example here at sea level I see 4.34v.
Then, start the engine. Voltage will drop indicating a vacuum present in the crankcase. For example mine drops to 4.25v idle cold, 4.14v warmed up fully idle.
It should drop even further while driving, 4.08v or something.

Then go wide open throttle and watch the voltage, it should drop to 3.5 to 3.9v indicating a pressure drop at WOT. Using a catch can will reduce some of the pressure drop signal because fluids require energy to be pulled through hoses and the more hoses and volume you have the more energy is lost as friction, thus you will lose some PCV action at WOT. If the can has a breather then the pressure will rise above atmospheric, a voltage over baseline 4.35v or higher. This crankcase pressure is forcing oil into oil seals, causing oil leaks. It is allowing blow-by gas to circulate throughout the engine and create deposits. It will degrade engine oil quality. You must ensure the pressure drops below atmospheric at WOT using any means necessary: vacuum pump, OEM pcv action, exhaust driven PCV, there are many ways to achieve it. Blow-by gas is harm full to the engine and pressure is a scalar unit which means it has no direction, once the vacuum signal is lost (map voltage higher than baseline) the blow-by gas has free reign over the crankcase oil orifices and engine oil quality will be lost.

https://www.corvetteforum.com/forums...post1605147175

I write extensive about PCV here
https://www.corvetteforum.com/forums...post1605206492

Apocolipse

You are overthinking it. The restriction is just so the car doesn’t suck in too much unmetered air during high vac conditions (steady state cruise) since it won’t be read by the maf. This is metered by the restriction in the valley plate to intake manifold. The valve covers you can open up all you want.

Kingtal0n

I have seen this type of valve cover singular restriction before in the valve covers on V6 modern engines with crankcase pressure sensors from the OEM such as BMW late models.

It is to produce a velocity component gas vector inside the crankcase. Without one side being restricted the two valve covers receive identical pressure drops which creates a stagnant component vector about midway in the crankcase, hindering PCV flow. I can draw a picture tomorrow if you like.

Turbo6TA

Exactly Right ...

Turbo6TA

If you plan on using the Holley LS valve covers, this is how I would plumb it .. (just my opinion)




As far as that breather in the Holley valve cover ... I would use this:

Fresh Air Inlet Breather / Filter
Hawks Motorsports
CBW-069B
https://www.hawksmotorsports.com/bil...-valve-covers/

Attachment 48333284

AzDave47

The instructions with my standard LS7 valve covers included this wording:

Remove the corresponding 1/8” NPT threaded plug on the Holley valve cover for the PCV connection. Use AT981662ERL (1/8” NPT to -6AN) to adapt to AN type PCV plumbing. If the OE 3/8” ID hose is being used, also add AT709167ERL (-6AN to 3/8” barb).

Here are the left and right side Holley valve covers. You can see the 90* fittings that come out of the valve covers and the spliced PCV check valve they specified that I spliced in where some of the hard OEM line previously was.

Apocolipse

Personally I would not cap off the sump tank - it needs to vent as much as possible to get rid of the bubbles out of the oil that the scavenge pump is dumping in.

herwawan

That'd be great!

Maybe I should've started with that - I'm using the Tall, dry-sump version of their valve covers, which doesn't have an oil fill, making it incompatible with a breather.

https://www.holley.com/products/engi...t/parts/241-97

Are you using a check valve on both sides? I can see it properly on the driver's side, but I am not sure if that's what I see also on the other side. I think we would only need it on one side, the driver's?

Also, are these the instructions that came with the covers? Mine have a different wording! You can see them here: https://documents.holley.com/199r11025.pdf

So the nipple coming out of the valve covers is just a 1/8" NPT plug? What is the reasoning behind switching to AN fitting? I assume it doesn't change the end result since you're still using the check valve and still going back to the sump tank?

Apocolipse

Btw did you already buy those valve covers? I’m going to be selling mine and already have all the proper threaded fittings / lines to adapt into a z06 dry sump setup.

herwawan

They are already in the car

I received today the PCV valve Holley recommended (Beck/Arnley 0450299). If I were to use it, I would've only used it on the driver's side but seeing AzDave47's post, I'm not wondering if they mean to install it on both sides. I don't believe so as the illustration they use is quite specific to the driver's side.

Also, the valve has an inscription on it saying "=> to manifold", to show a direction. I guess this would be to the sump tank in our application?

Apocolipse

You don’t need a valve - it’s not going to do anything other than fail one day

AzDave47

Yes their instructions indicated both sides. I have had them on for 15K miles and run the engine to 7300 RPM a good number of times with no problems. I have an Elite Engineering catch can on the circuit from under the intake manifold and only get oil when I run road course events. I get very little in straight line event or in my easy street driving.

The instructions were pasted from the instructions that either came with the valve covers or I downloaded. I don't know why they specified the parts or check valves they did but they seem to work. Both of the lines out of the VCs connect into the OEM hard lines (shortened for the check valve install) and go back to the dry sump tank.

Spaceme1117

This is the way I have been running the PCV system on my dry sump Grand Sport. I have the Holley tall valve covers. Hose runs from the dry sump tank to a tee. That tee then has rubber hoses running to each valve cover with a simple PCV check valve inline right before connecting to the valve cover ports. The Holley valve cover instruction even provide the part number for the recommended PCV valves.

Been running my car like this with an Edelbrok E-force and it works well. I don't lose any oil through the system and have never had any problems.

Kingtal0n

Without one side restrictor, blow-by gas may become turbulent and disorganized. Pressure is a scalar unit with no direction, velocity is only imparted to gas molecules due to a pressure difference and if both sides have the same pressure drop dp/dt there will be chaos instead of organization inside the crankcase gas flow. I made a picture quickly in paint because I know you are waiting to design the system so I rapidly produce this to help.


By restricting one side it forces the blow-by gas to organize and conserve their kinetic energy to flow mostly one direction, resulting with rapid removal of blow-by gas and increased energy efficiency on behalf of the PCV system.




3" Hg is roughly 1.5psi, 1.5/14.5 = .10 = 10% of engine power is 'stolen' by the PCV system in natural aspirated application to drive the crankcase depression at sea level in this example. Shoot for 0.5" to 3" Hg of post air filter pressure drop to organize the blow-by gas and drive the PCV system. Pressure drop of filters changes as they become clogged over time so its okay to start with a smaller amount than you wind up with.


It is necessary to remove the blow-by gas as quickly as possible to prevent,




Rapid sludging of oil, engine wear, Deposits, bad stuff happens if the blow-by is able to circulate into engine oil.
Always measure crankcase pressure. It also influence oil leaking

Here is an example of somebody using electric pump for PCV in crankcase pressure monitoring and control

https://www.evolutionm.net/forums/ev...l#post11930508

I hope this example helps put PCV into perspective. You must control the pressure somehow, electric pump, belt driven, exhaust driven, turbo driven, find some way to achieve the goal of low pressure in the crankcase. Monitor it using barbaric method of 1-bar map sensor and multimeter for low cost, or install a gauge which monitors and warns you like the above Evolution used.

Spaceme1117

In the Holley valve cover instructions, it says to use either the Beck/Arnley or Fram PCV valve if you are using the Holley Valve covers in place of the OEM ones. That is all you need to do. The Beck/Arnley part is $3.42 on RockAuto. You need two of these, some rubber fuel line hose, and some clamps.

The PCV system is simple; fresh air comes in from the intake, goes to the oil tank for the dry sump, then goes to the valve covers and flows into the crank case through the heads, flows the crank case through the valley plate, and finally into the intake manifold where it goes to the combustion chambers to be burned. The check valves you add just prevent the back flow of oil and crank case vapors.