I believe there is a rule about cross-posting links to other Corvette sites, so I won’t do that (obviously), however, there is a video from a certified Corvette mechanic on Corvetteblogger.com where it is definitively explained why any Corvette that has a dry sump oil system, and all C8s have a dry sump system, already has a catch can, so adding one is needlessly superfluous.

I might add that the power of marketing is very strong, especially when it comes to Corvettes, and we as enthusiastic owners have to stop and think if someone is trying to convince you that you “need” a particular product that a company is trying to sell you. A lot of times, the “need” is simply marketing designed to appeal to our desire to protect our emotional (more so than financial) investment in our Corvette​​​​​​.

Caveat emptor…

 

Just so everyone is clear on how the ventilation tubes function (note the red arrows indicating direction of airflow):

 

If you use a Tier 3 gasoline with detergents, street driving will clean away the oil on the intake valves... Now if you plan to do a few HPDE per year then again the Good gas will clean the intake valves. The only time I would install a catch can is if I were doing some frequent track time / racing.
But as I have said many times.... Do what you want to your car, it's your Toy so enjoy it.

 

I've never seen any compelling evidence demonstrating that catch cans actually produce any demonstrable benefits other than the visible evidence that they do catch a small amount of oil. I've seen no evidence that they prevent intake valve carbonization on DI engines. You see a lot of pictures of carbonized valves on engines without catch cans, but where are the pictures of catch-can equipped cars at the same point in their life-cycle showing clean valves?

I've seen no evidence that they are linked to increased engine reliability or longevity. They do make some folks feel better, so I guess that is a benefit of sorts.

 

You do know that the LT1, LT2 and soon LT6 engines are direct injected so the gasoline goes directly into the cylinders and never sees the back side (inlet) of the intake valves, right? What you said is somewhat true of carbureted, throttle body FI and port injected systems, but not the DI engines.

 

In an article written for SAE International Don Sherman (engineer and great automotive writer) said this about "catch cans" for the C8, I put in pics:






Never considered a "Catch Can" needed for my two C4 and C6 Vettes as gasoline flowed over the backs of the intake valves and was "continually cleaning" whatever crankcase "stuff" was coming thorough the PCV system into the intake manifold. BUT for the C7 with Direct Injection no such gasoline going over the intake valve backs, only PCV "stuff." BMW and Ferrari with Direct Injection high hp engines before the LT2 had issues. So I added one.
NOTE Pic is for Port, Throttle Body or Carburetor NOT DIRECT INJECTION



SIDEBAR
My experience with "Catch Cans." Don't Track so never would consider for my two C4s or C6 where gasoline flowed past the backs of the intake and washed away any crankcase material deposited on the backs of the hot intake valves. On my 2014 Z51 dry sump was "catching" once ounce of "stuff" every ~1000 miles. Used the same Elite Can on my 2017 Grand Sport. BUT waited to install as GM put a lot of time, effort and engineering and had a totally different PVC system. (They didn't do that because there were zero issues in the early C7s!) Many more line some in the valve covers. After researching and checking pressures assuming I did no harm I added the can. Collected less than half the amount of "stuff." Yep GM spent the engineering time and money and reduced the amount of crankcase "stuff" going to the intake. Removed the can as one comment from a GM engineer said a small amount of crankcase oil from the PCV system going over the intake valves steams provides some lubrication!

GM engineers are smart. They no doubt did an even better job on the C8. Yep still some small amount of "stuff" coming from the crackcase BUT from what Don Sherman notes, some drains back to the dry sump tank before it exits. If you track with a lot of WOT where more blowby is generated it may be somewhat effective. Your Car Your Choice.

 

Kraka, Thanks. And, as I read the instructions the UPR catch can installs in what is called the Foul Air path in the illustration you posted. That path does include a separator in the "engine block valley" that may or may not perform the function of a catch can, preventing oil from entering that path. I also reviewed the video you mentioned. With respect to the C8, he seems to say that the catch can function is already present in that the oil tank has baffles in the top - where the vent tube that goes to the rocker arm covers attaches. The problem I have with that explanation is that tube is the one called "oil tank ventilation" in the illustration above. But that is not the only path, and in fact that path does not go to the intake, and could not inject oil into the combustion chamber. On the other hand, the aftermarket catch can installs in the path called "foul air path" which does go from the crankcase (via an engine block valley separator) directly to the intake manifold where it is consumed by combustion. That is the path where the catch can is installed. And when installed, that aftermarket can apparently collects some oil. So is there normally no oil in that path (and the catch can causes oil to enter that path), or is there really some oil going though that path without the catch can, and if so, is that oil worth catching? I don't know the answer to any of those. Full disclosure - I do not have, and do not plan to get an oil catch can for my C8 - so I am not trying to justify it. I'm just trying to understand it.

 

I've often wondered whether catch cans create a situation where more oil is collected than would actually enter the engine if it weren't installed.

However, my main issue is that I've never seen evidence that they actually do anything beneficial. Everyone cites the DI issue of valve tops not being washed by gasoline, then make a giant leap of logic that catching a small amount of oil in a can eliminates the need for valve backsides to be washed by gasoline.

 

The Gen V LT engines have been around since 2014 but I don't think I've seen any pictures on intake valves with excessive carbon buildup on them, are there any documented cases of excessive intake valve carbon buildup on them? If so, what were their operating environments?

One would think that if this is still a problem that there would be some evidence by now.

 

I did not post that video as I'm attempting to not wade into this debate, again, but since you asked I'll attempt to respond. In the name of full disclosure, I did purchase two catch-cans for my C8, returned one, and sold the other. The 1st I bought was Paragon's and it was a total piece of crap with terrible fitment & alignment; it was returned. The 2nd I purchased was Corsa's and the overall quality and bracket design was far superior, as were the hoses (made in USA by Continental) and plastic fittings. With that said, after continuing to dig in and research, I made the personal decision not to install it on my car and sold the Corsa to another forum member. If I were to change my mind and buy/install one on my car at a later time, the Corsa would be the one for me.

During disassembly of my intake tract and associated PCV tubes, the inlet fitting of the foul air tube was oily with a thin film, but not outright wet & dripping while the outlet fitting that attaches to the intake manifold was dry with no oily residue. After removing my factory intake manifold, it did seem dry inside with no oil pooling, but I did find a little oil residue settling at the runner outlets around the flange gaskets at the head.

Do oil vapors travel through the foul air tube into the intake manifold? YES!
Is it anywhere near the volume experienced on the early dry-sump C7s? NO.

I sold my 2014 Z51 @ 70k miles and had the intake manifold off numerous times; yes there was some oil pooling in the intake manifold but I witnessed zero coking on the intake valves. I did not run a catch-can on my C7.

Here is a good tech thread to reference with plenty of info/details into the theory of catch-cans and how they perform in the real world: https://www.corvetteforum.com/forums...ispreloading=1

I've personally seen them cause more problem than they solve on the dyno, especially the cheap eBay ones that people just slap on with zero consideration to pressure and hose sizing. Everything from cars down on power, excessive smoking out the exhaust due to oil consumption, etc. Often times, simply reverting these cars back to stock PCV configuration has cured the issues on the spot with no major damage done. Again, these are primarily on the cheap generic setups that were not well thought out or designed for the specific application.

 

Exactly!

Having had two C7s and spending a lot of time in those forums, I've yet to see one reported that needed valve cleaning because of carbonization. I've certainly seen complaints on just about everything else on those forums.

I did see a picture posted by the owner of a C7 w/ well over 100K miles who posted pictures of relatively clean valve tops when his engine was partially disassembled for another reason. Oh yeah, his car never had a catch can.

 

My .02... I have other cars with catch cans. Their engine technology and design is different. The reason for the catch can for these is that the oil vapors run back to the intake. This causes quite a bit of sludge build up on the throttle body and other intake parts. Got tired of removing the TB every 10k miles and cleaning it. No problems since the cans were installed. Now, not sure if this is the same way the C8 is plumbed... just food for thought.

 

oopps .. My bad. Your right DI engines don't see benefit from gasoline washing over Intake valves. sorry for the miss info.

 

Depends what you think excess is! Tadge in 2014 said it was cosmetic. BUT they spent a lot of engineering effort for a complete redesigned PCV that was in my 2017 Grand Sport! They didn't do that for just a cosmetic issue!

Pics show the major difference in 2017 PVC system and simple system in my 2014. The prior like most cars drew air from the air intake after the filer and pulled crackcase "stuff" through a PCV valve directly into the intake manifold. This system is much more complex and I collected less that about half the "stuff" in the same can.
I'm confident the smart GM engineers did an even better job on the C8!


Since there was no extra air line to bring clean air into the crackcase, I installed a gauge to see where it was coming from as did not want to do any harm before installing the can. I found out!


A race car would never mess the carefully controlled air fuel mixture to each cylinder with crackcae "stuff." They just dump it on the ground as my two flatheads and my '56 small block before in early 1960s when the EPA said STOP and burn that crackcase blowby!


Some racecars suck the crackcase stuff out with the exhaust that also creates a small vacuum reducing windage losses and increase hp!

 

For a street car I'd say a noticeable decrease in power is excessive. For a track car I'd say a reduction in lap times is excessive.

 

Well to me any carbon debris (even small amount) left on the intake valves is an issue! Folks spend 100reds of hours porting intake passages and use tuliped intake valves to gain small added air flow. Don't need any baked-on carbon on the intake valves. That does lead to decreased power.

SIDEBAR
Have looked inside a number of engines including the Olds I put in my 1st car. Bought all in parts and had a freind taking an automotive course who prepared the heads. Heck could see myself in the combustion chambers. Valves were spotless.

Sponsored Richard Petty for over 15 years. Started when they were still in Level Cross, NC. When my folks went to deliver welding/plasma cutting machines or training I often went. Dale Inman would put me with one of their tech folks. Recall they had a new engine builder who was showing me the CNC intake ports in a cylinder head they just received. The closely spaced machining marks were slightly visible on the intake passages. He said, "I smooth those out but have not been able to measure a hp gain- BUT makes me feel better!" They were building their own engines at the time before "restrictor plate engines" made it more economical to rent, as they probably do now. There are significant differences.

When I retired (well semi) in 2000 built the 8.2 Liter BB for my street rod from some 30 boxes that came in a wood crate from Chevy. That 502/502 has CNC ported and matched intake manifold and heads. Can still see those huge shiny new valves. No they won't stay that way but don't want anymore "stuff" on the passages and valves then is inevitable. It that case the rich running 850 Holley double pumper has plenty of gas washing the PCV system "stuff" away! I did install the PCV system and didn't just dump it on the ground!


Perhaps if interest, I did not use a two outlet catch can on my C7s as do many folks who Track and talk about "stuff" building up on the throttle body. Wondered how it could be lower pressure on the inlet of the throttle body that than intake manifold. Intake air flows in pulses and at WOT that can be an issue so folks Tracking typically use "cans" with two exits, one hose going before the throttle body and one where the PCV system exits in the intake manifold. They can have crackcase stuff going on the intake side! More of a benefit for them than my street driving.
Again, I assume GM did an even better job for the C8 so I will not install!

 

I love your question. As a chemistry/math tutor & PhD mechanical MS/BS bioengineering/chemistry/biological science/mathematics it is quite clear to me by inspection the behavior of gas kinetics what seems to elude practically everyone.... it is not a secret? It is really a conceptualization from a chemistry book, that is the 'secret'.

First the purpose of pcv, PCV is engine cleanliness
The PCV system is intended to provide engine cleanliness for the high mileage and health of an engine, the PCV system prioritizes the engine crankcase components (oil orifice quality, lubrication, bearings, oil flow, oil control, ring function, ring cleanliness, deposit formation, and other cleanliness and oil control aspects) above all else. Originally seen as an emissions device, PCV has evolved into an engine cleaning, seal function and oil control feature.

Gas kinetics
Gas density, velocity, and partial pressure are definable features inside the engine crankcase related to engine cleanliness.
Gas molecules near room temp move 500 to 1000mph, colliding constantly with each other and the wall of their containers. This is why tires stay inflated at rest.
Warmer = faster, you drive the car tire pressure goes up due to gas heating. Higher pressure = more elastic collisions per unit time.
Oil molecules originally as a gas state are forming liquid droplets in crankcase gas due to collision with each other and their container, oil sticks to itself as a gas or liquid as they interact hydrophobically (hydrophobic interactions) and high gas density facilitates large oil droplet formation. Oil droplets forming under high pressure scalars with low kinetic energy velocity components gives rise to even larger droplets per unit time.
If crankcase pressure rises for any reason- excess blowby, leaking valve cover gasket, improper air filter pressure drop, gas density increases with crankcase pressure causing large oil droplet formation and coalescence, oil begins collecting to tube walls, flow paths, etc... more rapidly

Oil separation efficiency
PCV primary oil control point is crankcase pressure (Gas density) and oil separation (utilizing kinetic energy distributed adequately) and additionally a cleanliness aspect is partial pressure (dissolved gasses which are able to enter and leave engine oil over time are based on pressure).
The OEM oil/air separators are very good, even since the 80's pretty good. But there is no stopping high gas density which carries large droplets of oil from flooding into and collecting in the separators and invading subsequent lines and manifolds. An OEM air/oil separator IS a catch can, it is intended to catch oil and force oil back to the crankcase by taking advantage of gas kinetics (kinetic energy of the gas moving with a specific direction) which is a vector quantity, unlike pressure which is a scalar and has no direction.
The pressure scalar is a system wide collision and diffusion component of the pcv system and engine crankcase, while the kinetic energy is a velocity vector component of the pcv system & crankcase, and the two must be treated separately when comparing flow of gas within the engine crankcase (by the engineers or us when we modify the system) and their influence respectively.
Without sufficient kinetic energy (too much added crankcase volume or reduced input energy due to improper air filter pressure drop or inadequate vacuum pump operation for example) there may be insufficient oil separation by the OEM separator, leading to oil aspiration and baffles filling with liquid oil, oil inclusion (oil going places it should not be able to reach if the system was setup properly).
A pressure scalar will not work well to perform oil/air separation, the pressure scalar has no direction and forces gas molecules to collide all directions at once for a net velocity of zero, oil can combine to form large droplets and collect while it has no significant direction magnitude or moving very slowly , time to "condense" oil gas to liquid droplets in the gas suspension or onto surfaces. Additionally a high pressure scalar will force oil into engine seals causing oil leaks, and it will impact piston ring performance, forcing early ring switching and potentially causing ring flutter and oil accumulation of the ring pack.



Notice the axial force of crankcase pressure is a component of piston ring sealing, piston ring function, piston ring tension. A high gas pressure scalar in the crankcase will reduce ring function leading to additional blowby which causes even higher pressure scalar within the engine crankcase.
Thus the PCV system is not only an oil control feature, and engine cleanliness, it also serves to protect piston ring function and reduce blowby, improving the efficiency of the engine cylinder.

If you want to keep reading about PCV in performance applications I have posted many published details here
https://www.supraforums.com/threads/...#post-13987448

My opinion (discussion)
If anybody has gotten this far and realized that PCV is actually quite complex- surely you must also realize the extent of the knowledge from which the original engineers must draw from to design such a critical and effective evacuation for a modern high quality engine. If you trust them to design the engine, you buy the vehicle, to give you something so incredibly complex and powerful, -this work of art meant to be thrashed while maintaining reliability- but then doubt they can effectively design the oil system and think that adding a small tin can to the side of such an extravagant device is necessary? Why stop there, why not doubt the crankshaft bearing and change those as well? why not the guides in the head? Why not the timing chain, replace it with something superior? Why do people suspect just the PCV system but assume all the other parts are working well enough to be left alone. Something strange, marketing perhaps?

When you see a billion dollars of engineering & computer modeling and then people want to stick a $1 container inline somewhere because they think that they know better than a billion dollars of engineering... I mean. I'm not saying catch cans are bad- they can be utilized effectively in some situations for typical engines with wet sumps that have been turned up to 3x to 4x factory output. But this isn't a typical engine... this is a CX dry sump engine we are talking about here, the epitome of PCV and oil control features, not some corolla or honda engine that needs holes drilled in the baffles to facilitate drainage because you've increased the redline to 9k rpm and tripled the power output using custom forced induction and nitrous components.


Should it shock us that metal parts desire oil lubrication? The throttle valve is made of metal, usually. It will rapidly oxidize when exposed to constant flow of oxygen. Even aluminum will oxidize over time, disintegrate. Turbocharger compressor wheels desire lubrication. Valves- lubrication. A small bit of oil film is desirable. The OEM engineers know how much oil is leaving the crankcase and they have tuned the mass of oil such that it will maintain the quality and longevity of these components, be it throttle valve, compressor wheel, intake valve. If you prevent the oil from reaching the throttle valve and take the vehicle to 200k miles I can assure you there will be deleterious consequences, it may stick, or it may deteriorate. Unless you are manually lubricating it at maintenance intervals. I always remove my intake tube and WD40 the throttle valve, clean it with a towel and a pick, get the bit of debris or grit out of it. Same thing with turbo compressor, it needs occasional WD40 or similar to maintain a protective oil film. Metal materials everywhere in the world will crumble to dust if some lubrication is not supplied.

 

Of course the same thing is seen on forums for other sports cars, most especially people who want to change out the SPARK PLUGS, opinions being for both hotter and colder plugs. They change things around and then are asking for help to fix some problem(s) of their own creation.

 

The air filter is by far the best example for this. "upgraded" air filters are often the first thing we do as a novice to our performance vehicle... and generally this is the worst possible thing you can do without proper education and experience of how it will impact the engine health.

If the filter quality is insufficient it will enable trash and debris to accumulate in the engine, which ruins the cylinder, embeds materials to the head and deck (or intercooler/turbo) , wrecks the piston oil seal and piston materials. 'dirt' sand, pollen, fungus, dust, debris, gets into the oil system and facilitates deposits and carbon conglomerates. What is pollen and fungus made of? Why, the materials of life, such as Iron, Molybdenum, Sulfur, Carbon, Chlorine, Potassium, Sodium, etc... pretty much the entire upper half of the periodic table is inside fungus and pollen. If I asked you, "would you like to send iron, potassium, sulfur, chlorine, sodium, etc... into your engine today?" Would you say it was okay? Of course not. And yet people don't think twice about filtration particulate quality which directly impacts the ability of an engine oil system to remain clean and clear and the function of the piston rings.

Next, we have the PCV pressure drop. Not a big problem for dry sump engines which utilize pumps to drive most of the pcv action... but this is a major source of frustration and confusion for wet sump applications where people do not realize the importance of the AIR FILTER in terms of Crankcase Pressure PCV action.
At wide open throttle the only place to find a suction is between the filter and the throttle valve/turbo. All engines from all OEM manufacturers in the world provide a pathway from this region which leads to the crankcase. However, if you remove the air filter or 'upgrade' the filter to the point where it is 'invisible' (flows too freely) there will be no pressure drop in this region and subsequently no PCV action at wide open throttle, causing crankcase pressure to rise and oil begins to blow into the intake manfold and out of every engine oil seal over time.