The "Catch Can" Explained!

[Firebird2xc]

Also- does an upper induction cleaning need to be done differently after the catch can is installed? Should I do it right before, or wait until after, or does it matter?

Also- what does Chevy think of this? I asked my dealer about catch cans, and apparently the higher end models will have them included or as option sometime in the near future as OEM. They even had a photo in a Chevy issued catalog.

I'm not sure what they were promising as far as functionality, but it was kinda ugly. The Rx looks much nicer.

[White_SS/RS]

Is it normal to still be getting some oil in the intake?

I've had my RX can on since day one along with the clean side 1le oil separator. I'm at about 1300 miles with 250 of those on the track. I drained less than an ounce out of it today and looked in the intake and it's very lightly coated in oil.

[Camaro Dude]

To any of you who don't believe in catch cans, all I have to say is, thank Allah I installed my Elite catch can! Check out the pics with how much oil got collected during break-in period !!http://www.camaro5.com/forums/showthread.php?t=324052

[Apex Motorsports]

Originally Posted by White_SS/RS

Is it normal to still be getting some oil in the intake?

I've had my RX can on since day one along with the clean side 1le oil separator. I'm at about 1300 miles with 250 of those on the track. I drained less than an ounce out of it today and looked in the intake and it's very lightly coated in oil.

It is possible that your catch can is not catching all the oil and some is still getting through.

Originally Posted by Camaro Dude

To any of you who don't believe in catch cans, all I have to say is, thank Allah I installed my Elite catch can! Check out the pics with how much oil got collected during break-in period !!http://www.camaro5.com/forums/showthread.php?t=324052

That is insane.

[SIM2LS13]

Ordered my catch can today from APEX. I only have 1700 miles on my car, I shouldn't have much build up right?

[Agent WD-40]

Does anybody know what the difference between the V8 and V6 catch cans are? I'm assuming the can is the same but is it just different length hoses and mounting brackets?

[Elite Engineering]

Originally Posted by Agent WD-40

Does anybody know what the difference between the V8 and V6 catch cans are? I'm assuming the can is the same but is it just different length hoses and mounting brackets?

That's correct, different mounting bracket and hose routing. Otherwise the Catch Cans are the same.

[Firebird2xc]

Since I was ignored the first time around:

Tech Question:

I bought a breather cap for my oil filler tube along with my catch can. I've heard guys say that the 'unmetered air will affect your fuel/air ratio' but that's dumb. How would air enter the fuel air mixture via the crank case unless it was causing severe piston ring blow by? It wouldn't.

As I understand PCV systems, the PCV valve should close when the engine isn't generating internal pressure via combustion. As the crank case would also be generating oil pressure, and thereby excess gas pressure in the fill tube.

I'm assuming the filler tube cap is a check valve?

It only lets vapor out when the engine isn't generating oil pressure? That the excess gaseous pressure being vented from the crankcase prevents pressure from being exerted on the piston rings when the cylinders aren't being regularly pressurized?

Anybody?

[1Camaro2SS]

Has anyone taken a Rx catch can apart to see what the heck is in there? My Rx can barely caught any oil for last 3K miles. Seems i should have caught about a gallon of oil and gunk by now compared to Elite. Lol

[MrWray]

Originally Posted by 1Camaro2SS

Has anyone taken a Rx catch can apart to see what the heck is in there? My Rx can barely caught any oil for last 3K miles. Seems i should have caught about a gallon of oil and gunk by now compared to Elite. Lol

Maybe the internals are upside down

[911medic]

Originally Posted by Firebird2xc

I bought a breather cap for my oil filler tube along with my catch can. I've heard guys say that the 'unmetered air will affect your fuel/air ratio' but that's dumb. How would air enter the fuel air mixture via the crank case unless it was causing severe piston ring blow by? It wouldn't.

To understand how a breather could allow unmetered air into the intake, you have to first think about the complete PCV airflow path.

The entire system is based off of intake manifold vacuum.

Air is drawn into the crankcase on the "clean side." With the stock configuration, it is drawn via a hose that connects to the air intake tube AFTER the MAF sensor--which is important, because that means the system can account for that volume of air. With the breather cap, the stock hose is eliminated, and instead air is drawn into the clean side through the filtered breather. This volume of air does not pass the MAF sensor, and is therefore "unmetered" by the engine control systems.

The air travels through the crankcase and is eventually drawn out the "dirty side," along with the undesirable stuff that the catch can is meant to prevent being drawn into your intake. While in the crankcase, the fact that it's unmetered makes no difference, as you suggest. It's not becoming a part of combustion here.

This is where the unmetered part comes into play: after the catch can, the air is drawn into the intake manifold and is now part of the airflow that feeds the cylinders for combustion. The engine has calculated (via the MAF sensor) the volume of airflow that is on its way to combustion. Now there is extra air being sucked into the mix.

Now some breathers (like the RX brand) attempt to compensate for this by integrating a one-way checkvalve into the breather. This checkvalve supposedly restricts the amount of airflow into the system to a level that the engine computer can adjust for. Because (as I understand it), in addition to the MAF sensor information, the engine computer also looks at the O2 sensor data of the exhaust gases to determine if the engine is running too rich or too lean, and makes adjustments to compensate.

However, there are limits to the range of adjustments the engine can make, given the information it gets from the MAF sensor. So, if the checkvalve fails, or isn't really "calibrated" from the start to limit the air to within the range, you end up with messed up A/F ratios.

Conversely, if the checkvalve is too restrictive, under heavy vacuum you could potentially damage seals as the intake manifold can create very strong crankcase vacuum.

One other thing, pertinent to breathers with one-way checkvalves that only allow air to be drawn INTO the clean side: Under certain conditions (like WOT, or forced induction), intake manifold vacuum disappears. Now, if you have a buildup of crankcase pressure, it's not being drawn out of the dirty side, and it can't get out of the clean side since there the breather valve only lets air IN, not OUT. There's potential to damage seals that way, too.

Make sense?

Originally Posted by Firebird2xc

As I understand PCV systems, the PCV valve should close when the engine isn't generating internal pressure via combustion. As the crank case would also be generating oil pressure, and thereby excess gas pressure in the fill tube.

If you look at your PCV fitting, there's really no valve. It's just a hollow metal housing with 2 holes on one side and one on the other. The PCV system is a constant flow-through design that is always drawing air through the system as long as there is intake manifold vacuum. The oil pressure is generated after the oil pump (in the upper engine). The crankcase itself is not pressurized by design.

Originally Posted by Firebird2xc

I'm assuming the filler tube cap is a check valve?

It only lets vapor out when the engine isn't generating oil pressure? That the excess gaseous pressure being vented from the crankcase prevents pressure from being exerted on the piston rings when the cylinders aren't being regularly pressurized?

Anybody?

The stock filler tube cap does not vent at all. The stock clean side hose takes care of the PCV makeup air (as described above) and also allows pressure to vent out, if necessary, back into the main air intake tube, ahead of the throttle body. It's a closed system, and has to be, to meet emissions regulations.

If you mean your breather, it depends on which one you have. If it is the RX brand, it doesn't vent out, it only allows air into the engine, which can lead to the issues described above.

[Firebird2xc]

Originally Posted by 911medic

To understand how a breather could allow unmetered air into the intake, you have to first think about the complete PCV airflow path.

The entire system is based off of intake manifold vacuum.

Air is drawn into the crankcase on the "clean side." With the stock configuration, it is drawn via a hose that connects to the air intake tube AFTER the MAF sensor--which is important, because that means the system can account for that volume of air. With the breather cap, the stock hose is eliminated, and instead air is drawn into the clean side through the filtered breather. This volume of air does not pass the MAF sensor, and is therefore "unmetered" by the engine control systems.

The air travels through the crankcase and is eventually drawn out the "dirty side," along with the undesirable stuff that the catch can is meant to prevent being drawn into your intake. While in the crankcase, the fact that it's unmetered makes no difference, as you suggest. It's not becoming a part of combustion here.

This is where the unmetered part comes into play: after the catch can, the air is drawn into the intake manifold and is now part of the airflow that feeds the cylinders for combustion. The engine has calculated (via the MAF sensor) the volume of airflow that is on its way to combustion. Now there is extra air being sucked into the mix.

Now some breathers (like the RX brand) attempt to compensate for this by integrating a one-way checkvalve into the breather. This checkvalve supposedly restricts the amount of airflow into the system to a level that the engine computer can adjust for. Because (as I understand it), in addition to the MAF sensor information, the engine computer also looks at the O2 sensor data of the exhaust gases to determine if the engine is running too rich or too lean, and makes adjustments to compensate.

However, there are limits to the range of adjustments the engine can make, given the information it gets from the MAF sensor. So, if the checkvalve fails, or isn't really "calibrated" from the start to limit the air to within the range, you end up with messed up A/F ratios.

Conversely, if the checkvalve is too restrictive, under heavy vacuum you could potentially damage seals as the intake manifold can create very strong crankcase vacuum.

One other thing, pertinent to breathers with one-way checkvalves that only allow air to be drawn INTO the clean side: Under certain conditions (like WOT, or forced induction), intake manifold vacuum disappears. Now, if you have a buildup of crankcase pressure, it's not being drawn out of the dirty side, and it can't get out of the clean side since there the breather valve only lets air IN, not OUT. There's potential to damage seals that way, too.

Make sense?

If you look at your PCV fitting, there's really no valve. It's just a hollow metal housing with 2 holes on one side and one on the other. The PCV system is a constant flow-through design that is always drawing air through the system as long as there is intake manifold vacuum. The oil pressure is generated after the oil pump (in the upper engine). The crankcase itself is not pressurized by design.

The stock filler tube cap does not vent at all. The stock clean side hose takes care of the PCV makeup air (as described above) and also allows pressure to vent out, if necessary, back into the main air intake tube, ahead of the throttle body. It's a closed system, and has to be, to meet emissions regulations.

If you mean your breather, it depends on which one you have. If it is the RX brand, it doesn't vent out, it only allows air into the engine, which can lead to the issues described above.

Thanks man. I appreciate it. Looks like I'm returning the breather cap... Seems kinda crappy they'd sell an unknown quantity like that.

[Cheetoh]

I had one of the Breather Caps on My Camaro with a Magnason Supercharger, I ended up having to get a New Valley Cover, the built up pressure damaged the Original one.

[911medic]

Originally Posted by Firebird2xc

Thanks man. I appreciate it. Looks like I'm returning the breather cap... Seems kinda crappy they'd sell an unknown quantity like that.

Well, there's a lot that's been said about RX products/services, and I won't pile on.

I have their catch can, and I had the breather installed but have since removed it.

The catch can I have seems to work just fine, and the idea behind the breather is kinda OK, IF it restricts the air intake to manageable levels. But if the checkvalve fails (as some have experienced) or isn't really "calibrated" in the first place, you run into messed up A/F ratios.

Then there are the issues of excessive vacuum buildup, which I believe I experienced, and was concerned enough about possible seals/gasket damage that I pulled it and put the stock configuration back on. I don't think my breather let in enough air to make up for the intake vacuum, and I had a horrible squealing noise under the hood when vacuum was high.

And last, but not least, Ted Jannetty pointed out to me in another thread that the stock configuration allows 2-way air flow, which is important when intake vacuum goes down (FI, WOT, etc.). With the breather's one way valve only letting air in, under those conditions you can have excess crankcase pressure build up, also damaging the seals/gaskets.

In the end, it's just not worth the risk, IMO.