One of the best explanations for adding a catch can as i've seen

[Wild one]

Why we use catch cans - and some education for the people that repeat what they read without understanding the subject. From an engineer that also doesnt just build, but also designs endurance and sprint car engines.
Ok so in an engine, you have blowby. Even in a brand new NA engine (higher in FE engines because cylinder pressure is higher). That exhaust goes past the rings and into your crankcase a bit before it gets to the exhaust stroke. The more wear is on an engine, especially the rings, the more of this will get into the crankcase. That makes for positive pressure in there. It has to go somewhere. We use a 1 way pressure valve (PCV valve) to relieve the pressure before it starts blowing oul pan gaskets out of their seat and stuff.
Now that crank case has oil flinging everywhere, coating everything. Including the pressure valve, which is usually near the rocker galley and drainback holes. As the crank case pressure increases (with RPM or boost) the flow rate increases. Just as wind can carry a rain drop, this can carry oil mist. That oil comes up through the PCV and gets sent through a tube to your intake. If you take the hose off, you'll see oil dripping out of it. We do this because that crabk case exhaust is filthy and the EPA doesnt like it. So we send it back through the engine to sort if re-process it and burn more crap out if it for a cleaner exhaust signature. Yes this affects power a bit but youre talking like 0.1hp, very small. Unless its verry bad. And if it is, you have bigger fish to fry.
Now i shouldn't have to tell you this, but any time you pour oil into your engine's intake, thats not really good to do... along with random smoky starts being possible (not valve seal smoke, i mean little puffs and then its gone), other stuff that happens over time is carbon cakes. You know what those do. People think that because its a port injection engine that it cleans those off. Thats not how that works. It can clean the runners. Not the inside of the engine. This situation is why we have such high temp thermostats compared to traditional engines of the past. It doest need to be 210-230 degrees, it runs up there by design because that extra heat is what helps burn out the cakes. But if youve ever blow torched a carbon cake, you know thats not enough to get rid of it. It just reduces growth rate over time. Ok so we clear so far? That looses power after a while because intake and exhaust flow is affected by it.
But theres another thing that happens. That burnoff causes soot. This soot gets on your cylinder walls. That soot to our hands may feel like harmless powder. But if youve ever blown out a candle or another oil based fuel flame in pitch black and shined a flashlight at it, youll see a sparkle in there like glitter. That happens in the engine too. Know what that is? Microscopic diamonds... Yes that's a thing. Now imagine running just a drop of 10,000 grip diamond rubbing compound i your oil.... for 10 years if oil changes. What do you think will happen? Bearings, crosshatch, skirts, rings, valve guides, rocker seats, it all wears faster. It also washes that soot into your oil, thats how it gets fed to mains bearings. Thats why oil turns black, its all the same thing. But feeding oil into the intake makes *more* of it. This means oil gets dirty faster. So catch cans help keep it clean longer. Which is always nice to have, fresher oil to run on.
We use catch cans to catch that oil before it gets fed into the engine and does any of that. Its not required for an engine to run, which is why manufacturers don't put them on, unless its an exotic. Afterall why give you something that means youll buy a car 2 years after everyone else? No, ill save the money. See the mentality here? But on modern engines that cant just have a breather cap, its a good thing to have. It means your engine will stay newer longer and lose less power over time. It can also help it run better in general when its old and sensitive to stuff. In boosted engines, all of this is amplified.

 

[JHoward]

Why we use catch cans - and some education for the people that repeat what they read without understanding the subject. From an engineer that also doesnt just build, but also designs endurance and sprint car engines.
Ok so in an engine, you have blowby. Even in a brand new NA engine (higher in FE engines because cylinder pressure is higher). That exhaust goes past the rings and into your crankcase a bit before it gets to the exhaust stroke. The more wear is on an engine, especially the rings, the more of this will get into the crankcase. That makes for positive pressure in there. It has to go somewhere. We use a 1 way pressure valve (PCV valve) to relieve the pressure before it starts blowing oul pan gaskets out of their seat and stuff.
Now that crank case has oil flinging everywhere, coating everything. Including the pressure valve, which is usually near the rocker galley and drainback holes. As the crank case pressure increases (with RPM or boost) the flow rate increases. Just as wind can carry a rain drop, this can carry oil mist. That oil comes up through the PCV and gets sent through a tube to your intake. If you take the hose off, you'll see oil dripping out of it. We do this because that crabk case exhaust is filthy and the EPA doesnt like it. So we send it back through the engine to sort if re-process it and burn more crap out if it for a cleaner exhaust signature. Yes this affects power a bit but youre talking like 0.1hp, very small. Unless its verry bad. And if it is, you have bigger fish to fry.
Now i shouldn't have to tell you this, but any time you pour oil into your engine's intake, thats not really good to do... along with random smoky starts being possible (not valve seal smoke, i mean little puffs and then its gone), other stuff that happens over time is carbon cakes. You know what those do. People think that because its a port injection engine that it cleans those off. Thats not how that works. It can clean the runners. Not the inside of the engine. This situation is why we have such high temp thermostats compared to traditional engines of the past. It doest need to be 210-230 degrees, it runs up there by design because that extra heat is what helps burn out the cakes. But if youve ever blow torched a carbon cake, you know thats not enough to get rid of it. It just reduces growth rate over time. Ok so we clear so far? That looses power after a while because intake and exhaust flow is affected by it.
But theres another thing that happens. That burnoff causes soot. This soot gets on your cylinder walls. That soot to our hands may feel like harmless powder. But if youve ever blown out a candle or another oil based fuel flame in pitch black and shined a flashlight at it, youll see a sparkle in there like glitter. That happens in the engine too. Know what that is? Microscopic diamonds... Yes that's a thing. Now imagine running just a drop of 10,000 grip diamond rubbing compound i your oil.... for 10 years if oil changes. What do you think will happen? Bearings, crosshatch, skirts, rings, valve guides, rocker seats, it all wears faster. It also washes that soot into your oil, thats how it gets fed to mains bearings. Thats why oil turns black, its all the same thing. But feeding oil into the intake makes *more* of it. This means oil gets dirty faster. So catch cans help keep it clean longer. Which is always nice to have, fresher oil to run on.
We use catch cans to catch that oil before it gets fed into the engine and does any of that. Its not required for an engine to run, which is why manufacturers don't put them on, unless its an exotic. Afterall why give you something that means youll buy a car 2 years after everyone else? No, ill save the money. See the mentality here? But on modern engines that cant just have a breather cap, its a good thing to have. It means your engine will stay newer longer and lose less power over time. It can also help it run better in general when its old and sensitive to stuff. In boosted engines, all of this is amplified.

Absolutely, good explanation, Rick.

 

[Wild one]

Absolutely, good explanation, Rick.

It's actually not mine J,it's from a guy named Kyle Currier,he's an engineer that builds engines on the side for a few sprint car guys. I've had a couple go arounds with him over the years,but for the most part i agree with the majority of his posts,and this post of his, is one of the better explanations i've seen for adding a catch can.

 

[mikeru]

While I am a proponent of catch cans, I'm not buying the diamond dust theory. It takes tremendous sustained heat (between 900°C and 1300°C) and pressure (45 kbar and above) to turn carbon into diamonds. You just don't see those conditions inside an engine, even in the combustion chamber. Other things can crystalize and sparkle like diamonds.

My main reason for running a catch can is to keep the intake cleaner than it would be without a catch can. Residue coating the inner surface can eventually build up enough to potentially affect air flow. It's probably not by a measurable amount, but there are also sensors in the intake system which also get coated with this residue. So anything I can do to keep those sensors cleaner means they should last longer. It's probably just giving me a warm fuzzy in my thinking but it's worth the small bit of maintenance and cost. Port injection cleans the back of the intake valves and some areas of the ports in that area. But does nothing to clean anything upstream of them.

 

[Wild one]

While I am a proponent of catch cans, I'm not buying the diamond dust theory. It takes tremendous sustained heat (between 900°C and 1300°C) and pressure (45 kbar and above) to turn carbon into diamonds. You just don't see those conditions inside an engine, even in the combustion chamber. Other things can crystalize and sparkle like diamonds.

My main reason for running a catch can is to keep the intake cleaner than it would be without a catch can. Residue coating the inner surface can eventually build up enough to potentially affect air flow. It's probably not by a measurable amount, but there are also sensors in the intake system which also get coated with this residue. So anything I can do to keep those sensors cleaner means they should last longer. It's probably just giving me a warm fuzzy in my thinking but it's worth the small bit of maintenance and cost. Port injection cleans the back of the intake valves and some areas of the ports in that area. But does nothing to clean anything upstream of them.

His comment about it turning to diamond material might be a stretch,but i do know if you smash the carbon pieces off a valve and crush it,it definitely has a sand feel to it,and will scratch an aluminium surface,especially if you use a chunk of it and rub it into an aluminium piston skirt,so it's definitely hard enough to wear aluminium.
The combustion chamber temps aren't near high enough at roughly 900 to 1100 degrees,and with most cylinders operating at around 300 psi at light load and upwards of a 1,000 at higher loads,a high compression race engine with boost will see in excess of 1500 psi spikes at combustion, a diesal will see a bit more pressure at combustion,as i remember reading somewhere years ago,they'll see in excess of 2000psi at combustion,so there's definitely not enough pressure to turn the carbon chunks into literal diamonds,but the crap is still hard as hell in comparision to a piston,and can act like sand on a cylinder wall.
I have pulled intakes on high milege hemi's and literally had an oily mixture run out of them,and the intake port and valve will have a hell'va build-up of carbon,which does nothing to help with flow through the port and valve opening. A catch can won't keep the backside of the throttle body or intake port and valve spotless,but it sure makes a differance in build up though,and with how often the throttle body will need cleaning

 

[mboymopar]

Anyone running a catch can on a 3.6 ?

 

[Wild one]

Anyone running a catch can on a 3.6 ?

If you start a seperate thread on it Milo ,you might get a few more answers

 

[Wild one]

Anyone running a catch can on a 3.6 ?

I started a thread for you Milo,and tagged Nick.Sorry i couldn't help you out with one for your 2025 3.6
Rick

Catch can on a 2025 with a 3.6

@Nick@GotExhaust do you have anything that'll fit a 2025 3.6

www.ramforum.com

 

[NCRaineman]

Are you spending a lot of time at high RPMs? If not there is really little to worry about. Blowby at low RPMs is so minimal it barely rates mentioning. This is a "mod" that was popularized by racers and doesn't really apply to regular street driving.

Having pulled the intake and throttle body on my truck after ~50k miles, it was barely dirty... and I'm even running one of those high flow aftermarket filters that people claim do such a bad job.

 

[Wild one]

Are you spending a lot of time at high RPMs? If not there is really little to worry about. Blowby at low RPMs is so minimal it barely rates mentioning. This is a "mod" that was popularized by racers and doesn't really apply to regular street driving.

Having pulled the intake and throttle body on my truck after ~50k miles, it was barely dirty... and I'm even running one of those high flow aftermarket filters that people claim do such a bad job.

The airbox isn't the intake manifold,and the air filter really doesn't have much to do with what comes out of the pcv and crankcase.I think you're mistaking what a catch can does
A catch cans proper name is Air/Oil Seperator,and it's purpose is to seperate out the oily crap from the air,when it's sucked through the pcv system,so that it's not injested back into the intake manifold,"behind" the throttle body,where it techinically lowers the octane rating of the fuel going into the cylinder. The oily crap from the crankcase also coats intake runners and the back side of the valves where it turns into carbon,and with enough time restricts flow through the valve ports
Check out a Hellcats valve cover Ma Mopar uses Air/Oil sperators on all hellcats,it's built into their valve covers,but Ma Mopar also realizes the average owner won't maintain a seperate air/oil seperator properly,so they route the crap collected by the air/oil seperators back into the oilpan,where it dilutes the engine oil and introduces even more acids into the oil in the pan.

 

[NCRaineman]

The airbox isn't the intake manifold,and the air filter really doesn't have much to do with what comes out of the pcv and crankcase.I think you're mistaking what a catch can does

The PCV, which has a tube that feeds air from the crank case back into the intake. The claim people selling aftermarket parts make is that this dumps significant amounts of oil and other pollutants back into the engine. Yes, there is a little bit of oil that comes out. It is not enough to worry about unless you are spending lots of time at high RPM.

Do you race your truck? Do you spend a lot of time at the track or drag strip? If so then a catch can may benefit you. If you are just John Q Public using the truck in a normal manner and not flogging it around all over the place any benefit you'll see will be minimal.

This is exactly the same as companies selling "cold air" intakes and promising 10+ horsepower gains. Sure it looks cool under the hood. You'll gain some sound from the filter being more exposed. That's really it. It amazes me that people see through the intake BS on this forum but are all about catch cans. It's a gimmick, of course the people selling them are going to extoll their values... that is how they put bread on the table.

 

[Wild one]

Are you spending a lot of time at high RPMs? If not there is really little to worry about. Blowby at low RPMs is so minimal it barely rates mentioning. This is a "mod" that was popularized by racers and doesn't really apply to regular street driving.

Having pulled the intake and throttle body on my truck after ~50k miles, it was barely dirty... and I'm even running one of those high flow aftermarket filters that people claim do such a bad job.

Check out a Hellcat valve cover,that raised part that the pcv comes out of,is a factory air/oil seperator

Hellcat 6.2L HEMI Hellcat Valve Covers by MOPAR - MMX Modern Muscle Xtreme

Hellcat 6.2L HEMI Hellcat Valve Covers by MOPAR

www.modernmusclextreme.com

 

[Wild one]

The PCV, which has a tube that feeds air from the crank case back into the intake. The claim people selling aftermarket parts make is that this dumps significant amounts of oil and other pollutants back into the engine. Yes, there is a little bit of oil that comes out. It is not enough to worry about unless you are spending lots of time at high RPM.

Do you race your truck? Do you spend a lot of time at the track or drag strip? If so then a catch can may benefit you. If you are just John Q Public using the truck in a normal manner and not flogging it around all over the place any benefit you'll see will be minimal.

This is exactly the same as companies selling "cold air" intakes and promising 10+ horsepower gains. Sure it looks cool under the hood. You'll gain some sound from the filter being more exposed. That's really it. It amazes me that people see through the intake BS on this forum but are all about catch cans. It's a gimmick, of course the people selling them are going to extoll their values... that is how they put bread on the table.

I'm not really interested in arguing this point,as there's piles of pictures that disprove your theory,so we're going to have to agree to disagree.I run a can on my 300 and by no stretch does it get drove any harder then any other daily driver,and it collects it's share of oily crap in it's catch can.
You don't have any experience with a catch can,so do you think you're really qualified to make a judgement call on whether they're useful or not

 

[fitteenhundred]

I installed my catch can at around 34,000 miles on my 5.7 and every time I change the oil I'm glad I did. The motor doesn't use any oil between changes and I don't hot rod, too much, but I sure don't want that oily gunk being sucked into the intake. I won't be buying a new truck so I do whatever I can to make this one last.

 

[BossHogg]

Why we use catch cans

Here is why we shouldn't use catch-cans. No one keeps their truck long enough to reap any benefit that a catch-can yields. There is the engine bay "eye candy" factor, for what it is worth.

 

[CanuckRam1313]

For the naysayers...

With no oil catch can in use:

Have you ever taken your throttle body off and looked at the mess on its backside?

Have you ever taken off an intake manifold and see the mess inside of it?

This mess absolutely robs ones engine of efficiency, and if bad enough, output, too.

An oil catch can is a preventative and predictive maintenance piece that proves it works as described, every time it's opened up and emptied.

 

[CanuckRam1313]

Here is why we shouldn't use catch-cans. No one keeps their truck long enough to reap any benefit that a catch-can yields. There is the engine bay "eye candy" factor, for what it is worth.

Or, someone simply removes this item from ones current vehicle before trade in / selling, and installs it in the new vehicle. Pretty easy to do!

The benefits are proven every time it's opened and emptied... Just saying.

It is a functional item that works and not just installed to look good under ones hood.

 

[mikeru]

His comment about it turning to diamond material might be a stretch,but i do know if you smash the carbon pieces off a valve and crush it,it definitely has a sand feel to it,and will scratch an aluminium surface,especially if you use a chunk of it and rub it into an aluminium piston skirt,so it's definitely hard enough to wear aluminium.
The combustion chamber temps aren't near high enough at roughly 900 to 1100 degrees,and with most cylinders operating at around 300 psi at light load and upwards of a 1,000 at higher loads,a high compression race engine with boost will see in excess of 1500 psi spikes at combustion, a diesal will see a bit more pressure at combustion,as i remember reading somewhere years ago,they'll see in excess of 2000psi at combustion,so there's definitely not enough pressure to turn the carbon chunks into literal diamonds,but the crap is still hard as hell in comparision to a piston,and can act like sand on a cylinder wall.
I have pulled intakes on high milege hemi's and literally had an oily mixture run out of them,and the intake port and valve will have a hell'va build-up of carbon,which does nothing to help with flow through the port and valve opening. A catch can won't keep the backside of the throttle body or intake port and valve spotless,but it sure makes a differance in build up though,and with how often the throttle body will need cleaning

Rick, I'm not arguing that soot isn't abrasive, just that it doesn't contain diamond dust.

 

[NCRaineman]

For the naysayers...

With no oil catch can in use:

Have you ever taken your throttle body off and looked at the mess on its backside?

Yep. Pulled it off after 5 years and 50k miles... had a little bit of soot built up but nothing I would consider significant. Five minutes with a paper towel and some light steel wool cleaned it right off.

My truck is not a race vehicle. It does not spend significant amounts of time at high RPM, nor does it have forced induction. Those two things are what cause the most blowby. Under normal driving conditions that 99% of us do the modification is unnecessary, just a waste of money to put some pretty bauble under the hood. Now if that is what you like to spend money on, go for it. Just don't fool yourself into thinking some $50 part is going to make a huge difference in how your engine performs.

 

[Wild one]

I'm always amazed at the guys who have absolutely no experiences with a catch can,and have never had an intake manifold off a Hemi and looked at the inside of the manifold /intake port or the backside of the intake valve,but feel they know all about their lack of benefits.
As stated who leaves a catch can in place when they get rid of a vehicle,hell i still have my original Moroso catch can that was on my old 13 truck,right now it's on a buddies 6.4 Challenger.They aren't something that generally wears out,and can easily be moved from vehicle to vehicle when you change vehicles.
Most guys spend more on a night out then what it costs to buy a decent catch can,hell what you spend at Starbucks / Tim Hortons in a month on coffee would buy a top of the line catch can