I have a couple questions. I got a cam/heads 03 Silverado with a 4.8 swapped the original valve covers for some summit OEM LS valve covers or so I thought, turns out they are summit OEM ls3 valve covers. Once I completed the swap. I started it up and heard a very noticeable whistling sound coming from the CAI. Sounded nice almost like a mini supercharger but didn’t think it was normal since it didn’t do that with the original valve covers. Also the filler cap seemed to be getting sucked down because i had to use quite a bit of force to take it off the filler tube and the whistling would stop when i took the cap off. Did some research and asked a builder I know and had two options do a re route or a catch can. For the time being and because I didn’t want to drive to summit I did a pcv re route from a video I saw on YT where they connected both valve covers with a long hose and blocked off the valves on the manifold. I did the exact same thing except I used the stock filler tube (cause that’s what have right now). On the video they used fittings in place of the filler tube with a hose sticking out by the rear end of the truck. It seems to work because the whistling sound is gone. I went around the block to test it out and everything seemed normal, one thing I notice thought is it seemed like it had a bit more of a pep to it. Not that it was sluggish before, but it just seemed a bit more responsive. Anyway got home made sure the whistling noise was still gone and it was but when I removed the oil filler cap it let out a strong force of air (probably not articulating that correctly). So I was wonderig do ls3 valve covers work with this engine. If so does this re route work? Or is there a better way? Is a catch can a better option? The reason being the force of air that was let out when I removed the oil filler cap worries me because I don’t know if that means it’s building too much pressure somewhere and I don’t want to hurt anything. Is that normal and should worry about it? Will a breather fix that? I will attach pictures any input is greatly appreciated

thanks

 

All of your words hurt my head, and your pictures need markups and descriptions. Could you draw a diagram of your PCV piping?

 

I apologize, it’s my first time posting and I wanted to describe exactly what happened and what I did and not leave anything out. I attached new pictures with description. Basically all I did was attach a hose connecting both valve covers together Bypassing the manifold and I blocked off the two pcv ports where hoses from each valve cover should be attached. Every thing else stayed the same. After I was done I went around the block just to see if it would drive normal, even gave it a pull and everything seems normal but when I removed the filler cap after the quick drive. A very strong quick blast of air shot out the filler tube and that concerned me a bit because I don’t know if that means the crankcase has too much pressure and could potentially hurt the engine. What I’m asking is, was that blast of air normal? If not will a breather instead of filler tube and cap work better? is the way i routed the pcv the correct way? Will a oil catch can system work better

 

So you basically trapped all the crankcase pressure inside the motor?
you have to vent it out or else you will be blowing out all the seals and shooting the dipstick into your hood.

 

Whatever video you watched was terrible. Might Mouse catch cans has 100 different variations of routing PCV.

 

LS3 valve covers are no different than any Gen III/IV LS, right? Why did you replace them in the first place? Are you saying the new valve covers have different ports than your old ones? 🤔

1. The top intake port connects to the rear of the driver's side valve cover. On my catch can setup, the catch can is installed between these 2 items.
2. The brake booster connects to the rear intake nipple
3. The front passenger side valve cover connects to the throttle body. On one of those photos you can see the cap where that goes.

edit: Ho-Lee Chit Batman! I just saw both valve covers were hooked up together! 🤯 What the hell! Why?!

 

that’s not good. Good thing I have not turned it on since and just went ahead and put the old ones back on until I can get more information on what route I want to take. Now from what I’ve been seeing you can do pcv re route and attach a breather where the filler tube goes is that correct? Or install a catch can. The difference being a catch can can trap oil vapor from entering the intake and atmosphere. Is that correct?

 

I’ll give them a call and see what they can recommend. Are there any brands you recommend?

 

NO.

Absolutely NOT. Whatever else is right or wrong, THAT is a GUARANTEED FAIL.

The purpose of the whole PCV system is to continuously (well, almost) flush the crankcase out with fresh air. It accomplishes this by allowing manifold vacuum to suck dirty air out of the engine somewhere (stock, it's the driver's side valve cover) through a metering device of some kind, either an orifice or a valve; and by allowing fresh air into the motor to replace what it draws out, somewhere else (stock, the pass side VC), via a connection to some source of clean filtered air. Originally it was intended as an emissions control device, butt it also keeps the oil free of most contaminants such as combustion products, water (which is itself a combustion product), and of course, dirt. Very wise to keep it in proper operating condition in a street-driven vehicle; maybe not so much in a race car, butt definitely in a daily.

In a MAF system vehicle, ALL air that comes into the manifold, MUST pass through the MAF FIRST. The MAF (Mass Air Flow sensor) measures the MASS of the total incoming air; literally, that's a count of the # of molecules of air coming into the engine. By this measurement it knows exactly how many molecules of OXYGEN the engine is ingesting (assuming of course that the chemical composition of air is always the same, i.e. about 78% nitrogen, 21% oxygen, and 1% or less of everything else), and therefore, EXACTLY how many molecules of fuel must be added to it, to EXACTLY combine with that much oxygen, in perfect agreement and to perfect completion. This means that NO AIR must come into the engine that hasn't passed through the MAF FIRST; if any does, the ECM won't have any idea that it's there, and won't be able to add the right amount of fuel for it, and the engine will run lean as all hell ESPECIALLY at idle, with all the fuel trims wacked.

This means that a breather is a big no-no. Not just a no, it's a HELL NO. There is almost no surer way of creating idle problems (with idle being the time that the vacuum is highest, therefore a vacuum leak leaks the most, and also the air flow into the intake is lowest, meaning that even a TINY amount of unmetered air bypassing the MAF can have a MASSIVE effect) than that.

The CORRECT way to route the PCV with a MAF system is to connect the PCV valve to a source of manifold vacuum (i.e. the plenum BEHIND the throttle body), and to connect the makeup air intake (pass side VC port) to a source of air that's IN FRONT OF the TB butt BEHIND the MAF (which is over kinda near the coolant bottle). That way, the engine's air flow is ALL through the air filter and the MAF, with most passing through the throttle and directly into the intake, butt a small amount takes a detour after it's gone through the filter & MAF, from in front of the TB to the pass side VC, through the crankcase, back out at the driver's side VC through the PCV, and THEN into the intake.

Not sure why this is so hard. Seems to cause people ALOT of trouble wrapping their brain around it. It's so simple though, hell I don't even HAVE a brain, and I can figure it out. All you smart people shouldn't ever have any trouble with it.

There are some of our engines that are different; for example the LS6 has a port on the valley cover that hooks to the PCV, and a port in a VC that gets the makeup air. Minor difference at most; the only thing different is where the intake vacuum draws out of the crankcase from. You don't have that though, so it doesn't matter. You just have a grungy old stock 4.8 that needs a car wash, w shiny new VCs on it for some reason, looking goofy by being the only clean thing in that groaty sea of schmutz.

A catch can normally goes in the line from the PCV valve to ths intake, since air is flowing that way, and bringing oil vapor and whatnot with it. A catch can MUST BE sealed in a system like ours; NO BREATHER.

Now if you're running a speed/density tune, none of this about a MAF and breathers and all that applies quite so much; butt that's not the situation here. You still have the MAF. You need to hook it back up just like it came. Get rid of that silly-*** hose out in space there, un-cap the ports everywhere, and put the hoses back like they came. The port right behind the TB actually goes to a hole drilled through the TB from front to rear, thus that port is an access to plain old filtered & MAFed air, and should go to the port on the pass side VC, just like it used to. The port on top of the manifold is a hole in the side of the plenum with hard constant manifold vacuum on it, and should go to the PCV valve and then to the port on the DS VC, just like it used to. The valve usually sticks into the hole in the VC butt not always, you might have to use an "in line" valve instead, might want to look up the PCV valve for a LS3 car and see if that's what your particular VCs require. It's exactly the same thing functionally in any case, just with different connections. Put it together right and it'll work just like it's supposed to then.

 

I replaced them because they look old and a bit nasty from the inside and rather than clean them I just bought a new pair from summit (sum-440550B and sum-440555B) Well thats what I thought as well. That all ge3/gen4 valve covers were all the same with some upgrades over the years. I never thought changing the valve covers could make and engine perform differently. Shows I’m a noob but I’m sure you guys found that out pretty quick. The ports are the same but the inside does look a bit different. From what I was told it’s the baffling that’s different. Unfortunately I didn’t think to take pictures of the old ones and they are already installed. I only took a picture of the part number but I will attach picture I found on the web of the exact same valve covers.
Is yours a performance build? Or is it all the same and doesn’t matter? The only reason I ask is because what I’ve read theres different ways to route the catch can and I’m not sure if it’s dependent on your build. I’ve had this build for almost 4 years and I touted the pcv the same way it was before I did the performance upgrade. Which I’m guessing was the way it was from the factory. The only reason I i switched it to what you see in the pictures was because when I put the new valve covers there was a noticeable whistling coming from the CAI that wasn’t there before. So I got online and did some research and came to the conclusion that I was getting too much pressure in the crankcase and either needed a catch can or reroute the pcv. So to try and do a quick fix I got in the web again and came across a video that showed a pcv re route so I tried it with the only difference being they had an AN fitting with a 45 degree barb fitting attached to it and I had the filler tube and cap. I went around the block and while it did stop the whistling noise when I took the filler cap off a strong blast off air shot out and thought that wasn’t normal. But didn’t know where to go from there that’s why I resorted to posting on here. After a bit more research I came to the conclusion I should go with a catch can if I want to use those valve covers. My question now is which one is good for my build and how to route it