Yes, if he's removed the PCV valve, that might be a problem as I mentioned in post #19. He hasn't responded yet to tell us whether the PCV valve has been removed, or if it's been relocated to a place where it doesn't show in the picture.
The original question though was whether a vented oil cap and a catch can could be causing a vacuum leak significant enough to cause a ~40 horsepower loss (10 measured, plus maybe 30 expected from LT headers) and I'm still saying "no", if properly installed.
If the issue was poor running at idle or part throttle, your point might be well taken. I don't really know.

I don't know what you mean by "a recirculated line" but it appears to be just like the factory setup, but with the addition of a small filter. What's your point?

That's what I'm talking about too. See the post above.

Here's a question for you. Let's say he has a standard size throttle body with the blade fully open. At full power, roughly how many cfm is going though there?

At the same manifold vacuum, how many cfm is coming from his PCV system with several feet of 3/8 (max) hose, numerous fittings which are even smaller, and 1 or more 90 degree fittings?

Given the air flow from each, how much would the unmetered air flow from the crankcase change air-fuel ratios even without a PCV valve in place, assuming it's fresh air with normal oxygen content (which it's not, but I'll use a simple, worst-case scenario)?

Not trying to be argumentative.......there's just a lot of misunderstanding about how PCV systems work. I'd like to see understanding get better, not worse.

 

All I know guys is I replaced my stock oil cap with a vented cap and the car started throwing codes!!! so I said must be the cap so I took it off put back stock cap no more codes!!! Ive been to busy to try and figure out what happen there but something did and this post might help me do that- maybe???? I have 2000 this is a great forum ive leaned a ton here over the years!!!

 

A malfunctioning PCV valve? Just a wild guess...........

 

I disagree. Breathers have always been used on n/a motors in the past. The LSx PCV system design is poor to begin with.

After putting in a breather cap, it reduced my oil consumption significantly. Or in this case, oil to the intake manifold. and its not the catch can collecting more because the level on the dipstick is consistent.

im no mechanic but im just giving you my "real world" results

 

Interesting...sounds right the N/A motors used the system for years.
Where is ET when you need him? Bet he can come up with an answer for all of us....

 

...might have something to do with improved engine building over the years since the PCV was initiated on carbureted motors...better ring sealing, closer tolerances, yada, yada, yada...

 

Virtually every car in the old days had a breather in the fill cap on the valve cover. It was usually a bit gooey but worked fine.
Of late the breather is not legal nor is the vented gas cap, as it is a fumes issue.
Since 97 the Vette has had no less than 6 PCV iterations. Early ones vented both valve covers to intake thru dual "PCV valves" which were the old check valve type. In 01 the valley cover vent emerged with a 4 " hose to the intake the "PCV Valve" was a just a restrictor, and in 04 the "PCV valve" was gone and there was no vent on the driver's side valve cover. Starting with the 05 LS2 there is a restriction built into the valley cover vent and no "PCV valve", and the pass side valve cover vent goes into the air intake in front of the TB. In 06 they are retrofitting with a restrictor type "PCV valve" I got one in the mail and it looks like the 01 Version but like most of the guys the LS2 side we don't know where to put it. If you look at the PCV system schematic for 05 there is no "PCV Valve"
The bottom line is GM is struggling to find a way to seal the crankcase to atmosphere and not suck air into the intake. I have tried every one of theses deals and various catch cans and breathers without a real winner. If you close the throttle from higher rpms with a standard trans in gear you will suck oil into the intake with any of the prescribed GM schemes cause you create a vacuum in the intake manifold. Not so bad in automatics. Ask the guys with 05s and 06s. They have reinvented oil consumption issues.
A breather sorta works with or without all or parts of a PCV system. If it has a filter it will keep bad stuff out when sucking and get gooey when venting. It is not an option for the car manufacturers but is an old school solution for after market.
Results will vary based on lots of variables.

 

Nice


DH

 

How about a check valve in the line from valve cover to TB or Airbridge/Coupler. That would allow flow of air into the engine (metered) but no oil to flow in the opposite direction ?????????

I may try it this weekend.


DH

 

You ever stop to think that the reason you are NOT consuming oil is due to the fact that the PCV system is no longer "Pulling" the vapors/oil out??? Now its only working in a neutral pressure situation. Which is the exact opposite purpose of a PCV system.

By adding a catch can and NOT using a breather, you are now "Pulling" the junk out of the motor as well as trapping it in the can.
Hence the reason vaccum pumps are so popular. They "Pull" the vapors out.

 

N/A motors were also setup in "Speed Density." By eliminating the MAF, you eliminate the need to meeter the air intake..

 

But heres a couple of points to think about..

1) In the old days the cars were MAFLESS.. So there was no need to meter the air..

2) In EVERY situation you talked about, ALL of them were closed systems. They were never vented into the atmosphere. Which means, when the car is drawing air it is pulling 100% of it through the MAF sensor.

3) I agree that the PCV valve has been an issue for a looooong time. BUT if you REMOVE the PCV valve, then take the oil filler cap off and drive the car, it will ingest a **** load of air THAT IS NOT METERED BY THE MAF.. WHY??? Because the air that the motor is drawing is drawing it from ANY available source. It will be pulling it through the MAF and through the valve cover. The motor will think it has X amount of air, but it is really ingesting Y amount of air... This will cause driving and power issues.

4) REGARDLESS of wether or not you run a PCV valve. You should NOT run a breather on a N/A motor that is being monitored by the MAF..

If you dont believe me, drill a hole in your intake.. Watch how it drives.. Your doing the EXACT same thing when you attach a line from a "Vented" valve cover to the intake..

 

In theory it "Could" work. The only problem you run into is the cracking pressure of the valve. You would want to run it low enough so that it could work, but not so low that the motor could pull it open..

 

How would I know if it was working or not ?????
What should I look for ?????


DH

 

If he's added a breather and made no other changes except a catch can, the PCV system is still "pulling" vapors from the crankcase as intended.
Oil consumption is probably reduced because engine blowby at full throttle, instead of back-flowing into the throttle body when it exceeds the capacity of the PCV system, is now exiting at the breather.

Howie, that's something to think about with your checkvalve. If you eliminate that second path for excessive blowby, you might generate some crankcase pressure. Cars with the "orifice" type PCV valve especially need this second path. If you get excessive crankcase pressure, it will show up first as the dipstick being unseated (pushed up slightly). Watch for this.

Vacuum pumps have never been terribly popular. Under some conditions, they'll increase power by reducing air density in the crankcase, but the power increase is pretty small given the complexity and cost. On an all-out race car with room to mount the belt drive and a special low-tension ring package to take full advantage of it, it might be worth it.
A factory PCV system will not generate anywhere near this level of vacuum. Some people restrict the supply side of the PCV system (from the throttle body) to generate crankcase vacuum, but this vacuum disappears at full throttle, exactly when you'd need it most for a power increase.

If you don't have oil consumption issues and aren't blown, there's probably no advantage to having a breather.
As far as problems go though, many forced induction guys (including me) run them all the time with no metering, tuning or driveability issues. I don't see any basis for the strong warnings and paranoia about breathers from "someone" in this thread. Fortunately there are many others posting on this thread who truly know their stuff. Be careful who you take advice from.

If you want to run a breather, the best one probably comes from East Coast Supercharging. It screws on just like the factory oil filler cap with no modifications, doesn't make a mess or drip, and clears the hood.

 

Warp Factor's post hit the nail on the head. His post explains the N/A motor quite well. Thanks!

 

The pcv valve allows the gases to come from the valve cover to the intake and keeps air from flowing back into the valve cover. If you have a breather on your valve cover there is nothing stopping the direction of air to flow from outside through the breather into the valve cover and throughthe PCV valve and into the intake. This will constitute a vacuum leak. It will, it can, and it was on that setup, it is that simple. Was it alot....no I doubt it, does it have to be that much to screw up the map readings? Drill a little hole in your intake and find out.

 

No need. Dozens of us run breathers without any issues. It's recommended by many top tuners for FI. My tuner put it on my car himself. With all his scanning and tuning goodies and experience, he'd know if there's a problem. Car runs fine. Other cars of his run better than fine. Good enough for me.

 

We aren't talking FI now are we. I doubt you have your pvc hooked up if you are running FI or you would be pushing air back into the crankcase if you are running any amount of boost.

So, back to this topic of NA with a pcv valve along with a breather.

 

I didn’t read through this whole post..... But can tell you this is a very bad idea. I accidentally put a one-way valve on the fresh air draw on the intake when I did my LS2 swap and blew my dipstick out twice on the dyno(made a nice mess). When you go WOT you no longer have a vacuum pulling the gasses from the crankcase. The crankcase pressure increases and depends on the fresh air and pvc valve/lines to release the pressure. If you plug one of the ways for the gas to escape you will blow your dipstick out or possibly a front or rear main seal.

To recap gases need to flow in both directions....