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When the C7 came out it was the 1st high performance engine Chevy had with with DI (mine was built in September 2013.) Hi performance engine intake valves get hot and oil from the PCV system can bake on the backs. No gasoline passing over them all the time (as in my C4 and C6 Vettes) to clean it off! At the time, there were other high performance DI engines that had been out prior to the Corvette, like Ferrari, was saying they were planning to offer an annual service to removed the Coking chemically. They did not as that does not work! Once the oil bakes on it's not easy to remove. BMW on some of their early DI engines had a walnut blasting procedure to remove coking.
Just watched a video that tried to show why the C8 does not need one because it has a dry sump tank and all dry sump tanks have one in the tank! Problem with his logic is the early C7 dry sump had significant oil going through it's simple PCV system. GM spent a lot of time and money improving the dry sump system for the 2016 and later dry sump cars (had that in my 2017 Grand Sport- much more complex, many more and different lines. They didn't spend the time and effort because it was not an issue at some level. Funny, the video also mentions the Camaro LT1 which GM installed and internal "catch can" as proof it can be done. BUT he didn't mention that in an "Ask Tadge" Forum Post he side steps the question of why the C7 wet sumps didn't use that system (and they did not.) He simply said you can get the dry sump!
Yep, I'm satisfied the GM engineers further developed the LT2 PCV system and incorporated what they could to mitigate the issue. However if Tracking is a significant parentage of usage can also see where a catch can could be useful.
Here are a few pics. Included one for folks who don't understand this issue came up because in ~1960s the EPA said stop dumping crackcase blowby in the air! Suck it up and burn the stuff! Hench the PCV system was introduced. All was OK when gasoline was passing over the intake vales continually. It washed it away IF it contained enough cleaners! Then came DI!
The flathead that came in my '41 Ford, my '50 Ford and 56 Chevy small block all had "Road Draft Tubes!" They just dumped the crankcase blowby, oil turned into oil mist by the spinning crack etc into the air!
Yep, early hi perfdormcne DI engines had "coking" issues. BMW had a walnut blasting procedure!
The GM engineers did what they can to reduce the issue. This pic shows they incorporated baffles in the top of the dry sump tank to act as a catch can. Would be good to have a diagram of the PCV system air passage to see how the crackcase blowby, oil mist created be the spinning crack etc gets trapped before it goes into the intake manifold.
Prior to the early 1960's when EPA said STOP dumping crackcase blowby into the air. Suck it up and burn it in the combustion chamber! Prior a simple "Road Draft Tube" just put it into the air! Even my '56 Chevy small block had a can filled with steel wool and a tube that went down to the ground!
Technically, you are modifying the emissions control system. I doubt any of the manufacturers have CARB certification. If you live in an area that requires periodic smog inspections you might have a problem. There have been cases posted on the internet that some people have had warranty problems because a catch can was installed. But I suspect most dealerships don't care.
Personally, I don't believe they are necessary on a street driven C8. I haven't seen any documented cases of excess carbon buildup on C7 valves. And you have the added hassle of removing the engine cover to empty the can on a C8.
UPR's can be emptied without removing the engine cover on the HTC. That's a major advantage. Paragon's requires you to remove the cover every time you want to empty it, which should be about every 1,000 miles.
I believe that there are several videos out there from the Chevrolet engineers that detail that the LT2 has several "catch cans" built into the design of the engine and that any additional catch can is superfluous.
And none of those videos about the "built in " devices address the path from the PCV valve to the intake, which is the real problem and what a catch can helps resolve.
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Yep, as I noted in Post 19 it would good to have a detailed path for the PCV oil mist and oil vapor going to the engine to be burned. Although the video I sighted in post 19 said that was above the baffles in the dry sump tank, was not sure of his facts from some other comments.
BUT a written text from Don Sherman, who is an excellent automotive writer (engineer and Corvette racer) describes the system. Although still not a total diagram it clarifies what the pic I posted shows. I'll quote the key parts re condensing oil vapors and oil mist prior to going into the engine to be burned. I consolidated and shorted the first 2 lines into one at the start: "The LT2 molded-plastic oil dry sump reservoir serves several purposes. Oil scavenged from the valley and the shallow cast aluminum pan covering the bottom of the engine drops through a maze that separates liquid from vapor. After settling a few moments in the tank, vapor bubbles disappear, leaving only liquid oil. Vent lines attached to the top of the reservoirroute the vapor to the LT2’s valve covers where it’s drawn into the intake plenum by engine vacuum.
An exit passage at the bottom of the reservoir feeds the crankshaft-driven variable output oil pressure pump with no need for external lines that add weight and inhibit flow."
Looks like the video that discusses the lack of need for a C8 Catch Can had the description of how the oil mist and vapor left the dry sump to be burned by the engine was correct. Not a complete path but a good pic with Don Sherman's description.
And none of those videos about the "built in " devices address the path from the PCV valve to the intake, which is the real problem and what a catch can helps resolve.
Except nobody seems to be able to actually find a problem that they catch can resolves. C7’s had no problem. C8’s don’t seem to have a problem, yet everybody seems to think they need to reengineer their engine with some cheap aftermarket parts they discovered on YouTube.
UPR's can be emptied without removing the engine cover on the HTC. That's a major advantage. Paragon's requires you to remove the cover every time you want to empty it, which should be about every 1,000 miles.
Yep, takes about 2 minutes total. Amazing what that thing catches and I empty out. All of which would be on my valves and manifold otherwise.
Yep, takes about 2 minutes total. Amazing what that thing catches and I empty out. All of which would be on my valves and manifold otherwise.
I’ve scoured the internet looking for C7’s with coking issues. Came across a lot of articles justifying a catch can based on the evidence that oil gets caught in it, but have yet to find anything showing C7 engines actually suffering because they didn’t have one.
You’re probably finding oil because a can is installed in the path it would have taken back to the sump anyway.
Direct injection has been out for decades. I’m sure if GM can make the rest of the engine they can figure out what to do with some blow by oil.
I remember when I bought my C7 in 2014, there were a lot of people posting pics on this forum showing how much oil was in the intake manifold and getting to the valves. Somewhere in 2016 or so GM changed the path of the PCV system so it was a bigger issue early on. Im not taking any chances on this engine, its cheap insurance. There are several things GM has chosen not to do or has one scratching their head on at times, you keep doing it your way, I'll do it mine and we will both sleep great at night!
I remember when I bought my C7 in 2014, there were a lot of people posting pics on this forum showing how much oil was in the intake manifold and getting to the valves. Somewhere in 2016 or so GM changed the path of the PCV system so it was a bigger issue early on. Im not taking any chances on this engine, its cheap insurance. There are several things GM has chosen not to do or has one scratching their head on at times, you keep doing it your way, I'll do it mine and we will both sleep great at night!
I remember when I was younger getting baited into doing a throttle body and manifold cleaning whenever I took my car in for an oil change. They would show me photos of what dirty intakes looked like. More often or not I’d end up with more problems than they solved. When I ignored the intake cleaning and just followed the manual I didn’t have any problems.
Not saying a catch can will cause problems, but just because an engine part is dirty doesn’t necessarily means it needs to be cleaned.
GM does make some baffling design decisions but their engines have proven to be pretty reliable.
I sold my 2014 Z51 after 7 years & 70k miles. I had the intake manifold off numerous times to swap on different parts and saw zero evidence of valve coking. I've also had my C8's intake manifold off with the same result. Modern high-performance oil is also formulated accordingly. Not only did GM engineers take this into account, but so did the Mobil 1 (especially with their fancy new Corvette-specific ESP formula).
You’re probably finding oil because a can is installed in the path it would have taken back to the sump anyway.
Wrong!
In my 2014 C7 Z51 Crankcase oil vapors, burned oil drops that come out of the crank and rod sleave bearing and hit the hot cylinder walls, combustion blowby, etc come out the PCV system through a PCV valve and directly into the intake manifold through a short hose. Not much different than what I installed on the 8.2 Liter engine in my Street Rod. Any baffling occurred "before" the PCV valve NOT after where the Catch Can was placed. Put a quality, baffled "Catch Can" in the line and you condense and collect some of that oil and mist. I was collecting, as many street driven cars reported, ~1 oz/1000 miles. 1 oz that could not bake on the hot intake valves.
My 2017 Grand Sport dry sump had a far more complex PCV routing. GM spent a lot of money and engineering time fixing that "no problem" in all dry sumps after 2016. See pic below. Some of that crankcase oil and mist went 1st into the valve covers, (it appears similar to what Don Sherman stated occurs with the C8.) Pics below shows what I carefully checked before putting my "Can" taken from my Z51 to my Grand Sport to assure I was doing "no harm." I was collecting about 1/3 the prior amount with the same "Can!" In fact, sufficiently less the "Can" IMO was not needed. I "assume" (and from Don Sherman written comments) GM engineers did an even better job in the C8.
BTW, although GM added what was called a catch can in the wet sump LT1 in the Camaro that drained some of the oil and mist back to the pan, Tadge even said in a forum post they didn't in the Corvette as essentially you could opt for a dry sump. (Assume they thought folks who bought the base car -after the Grand Sport came out a small percentage- didn't use WOT very much and would never cause a significant enough issue to "feel" the difference! -said Tongue-In-Cheek as know you bought a base C8 ) Actually the situation is worse for Trackers or those using a lot of WOT. When the manifold vacuum is low, more crankcase oil is being pulled into the engine intake through the PCV system. In fact, the Catch Can system becomes more complex needing extra lines.
Nope, it's not so simple with a high-performance engine where the large intake valves get very hot (~1000F when using max power) and some oil will instantly bake on the valve backs. Won't clean off with solvent. Yep, a grocery getter DI or a Vette always driven like a grandma may never feel a performance difference.
BUT GM is not spending all that time and engineering effort to improve a "no problem." AND those earlier high-performance DI motor engineers like Ferrari and BMW are pretty smart as well!
Before I installed the Elite Catch Can that baffled and condensed the oil mist etc in my 2017 Grand Sport wanted to be sure I did "no harm" as the PCV system was entirely different. GM engineers spent a lot of time and effort reducing that "No Problem" issue with lines going into the Valve covers etc.
The 2017 PCV system eliminated that separate line identified for the 2014 dry sump as bringing fresh air from the filtered air intake into the crankcase. It is there to replace that air etc being sucked out by the PCV system. I validated how the fresh air was entering in the IMPROVED 2017 dry sump system! GM didn't spend the time and engineering effort to IMPROVE a nonexistent issue!
But the output of the PCV valve does NOT go into the oil tank. Ever. Period. It goes straight into the intake manifold, where the oil vapor gets to coat everything it touches.
Originally Posted by JerryU
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Yep, as I noted in Post 19 it would good to have a detailed path for the PCV oil mist and oil vapor going to the engine to be burned. Although the video I sighted in post 19 said that was above the baffles in the dry sump tank, was not sure of his facts from some other comments.
BUT a written text from Don Sherman, who is an excellent automotive writer (engineer and Corvette racer) describes the system. Although still not a total diagram it clarifies what the pic I posted shows. I'll quote the key parts re condensing oil vapors and oil mist prior to going into the engine to be burned. I consolidated and shorted the first 2 lines into one at the start: "The LT2 molded-plastic oil dry sump reservoir serves several purposes. Oil scavenged from the valley and the shallow cast aluminum pan covering the bottom of the engine drops through a maze that separates liquid from vapor. After settling a few moments in the tank, vapor bubbles disappear, leaving only liquid oil. Vent lines attached to the top of the reservoirroute the vapor to the LT2’s valve covers where it’s drawn into the intake plenum by engine vacuum.
An exit passage at the bottom of the reservoir feeds the crankshaft-driven variable output oil pressure pump with no need for external lines that add weight and inhibit flow."
Looks like the video that discusses the lack of need for a C8 Catch Can had the description of how the oil mist and vapor left the dry sump to be burned by the engine was correct. Not a complete path but a good pic with Don Sherman's description.
But the output of the PCV valve does NOT go into the oil tank. Ever. Period. It goes straight into the intake manifold, where the oil vapor gets to coat everything it touches.
No what Sherman is saying nor what changed from my 2014 Z51 dry sump to my 2017 Grand Sport dry sump system.
BUT agree I have not seen a complete PCV flow path. Perhaps like the LT1 wet sump system where GM did install a "catch can" as some called it and Tadge said it drains back oil and oil mist to the pan, the C8 has several of those "drain back systems" and baffles reducing what gets to the intake manifold.
Decided that even though a majority Won't Care, I'll post some technical details. That includes a usual target for some posts, the ~1000 Silent Majority who viewed this Thread and those that will, but will not post, versus the ~15 of us Vocal Minority who did.
But will make it all a sidebar so those who think it's all BS, "GM would have added if it were needed" etc OR whose eyes roll with the presence of NUMBERS & MATH! Just scroll past!
SIDEBAR.
I'll do it with pics and captions:
Yep, as Don Sherman said with the C8 the outlet from the dry sump tank containing some crankcase "stuff" goes to the valve covers and then the engine intake. But where does the air and "stuff" come from if NOT the PCV system?? ANSWER: THE OIL AND AIR SCAVANGE PUMPS- The C8 has 3! Some racing engines use very large multiple oil/air scavenge pumps to create a vacuum, which can add significant hp! One said they achieve 10 psia crankcase pressure (a 4.7 psi vacuum) and gained a 15 hp at high rpm! The crank and rods have less windage hp losses spinning in the lower density air. Yep, imagine the tornado that is an 8500 rpm spinning C8 Z06 crankcase!
When I researched why there were two "Catch Can" connection options, one with an extra hose and flow check valve that went to the air intake tube- wondered why. The pressure always has to be higher before the throttle body that inside the intake manifold to flow air through the throttle body. It can't be lower? Or can it?
Below is a pic I use in my welding gas flow business discussions. It's for Argon and CO2 but same for air just have to use the proper densities. From the pic above, the “catch can” is added between the crankcase, P1 and the intake manifold P3. Using those equations to define flow into the engine at WOT. At 6500 rpm the air flow will be about 700 cubic feet of air per minute (CFM.) That assumes 100% volumetric efficiency. The throttle body is 3.4 inch (87mm) diameter. If the pressure at P2 is atmospheric, 14.7 psia, then to flow 700 CFM of air through a 3.4 inch diameter hole (forgetting losses due to the throttle plate etc) would require about 0.5 psi higher P2 pressure than P3. Therefore the manifold pressure P3 would be about 14.2 psia. PCV flow is based on the crankcase pressure probably being about atmospheric with oil/air scavenge pump suction offsetting a possible positive pressure.
So why are some Catch Cans adding a second line to take air from after the air filter but before the throttle body?? The AVERAGE pressure MUST be higher before the throttle body to achieve 700 CFH flow on Average?
The answer is because the air flow into an engine and through the Throttle Body occurs in pluses and the AVERAGE is higher BUT there are low pressure peaks! Some of the Catch Can manufacturing folks discuss in much more detail. BOTTOM LINE: It's not simple to say just where the crankcase oil, oil mist, burnt oil that comes out of the rod and crank bearing, hits the spinning crank and lands on the hot cylinder walls and piston bottoms, as well as combustion products that get past the rings - will go.
GM knows all the pressures and just where it all is going. They improved the dry sump PCV system in my 2017 Grand Sport over that in my 2014 Z51 so I captured only ~1/3 the oil in the same quality Catch Can. IMO, it was probably not needed in the Grand Sport for my, albeit often aggressive, street driving. The GM engineers have improved it further in the C8.
Now, if mostly Tracking a different story. Like a race car don't want more of the Crankcase "stuff" screwing up your air/fuel mixture! Race cars often just dump it in the air or suck it out with the exhaust and create slight negative crankcase pressure!
Those are some great replies guys showing the flow for those who dont understand it. And those same people can choose not to add a cc, end of story. Without a separate reservoir that can be emptied, the oil and water vapors and combustion byproducts are either going into the intake, or back into the oil and Ive seen the look of what I dump out and I dont want it back, anywhere! So I will run my cc and have peace of mind doing so.
For those who haven't seen any bad results taking the manifold off, that is great news! I have seen others (myself included) who know first hand what happened before a cc was installed (C7). I do think GM does a better job in their design than Audi, VW and BMW had done, a lot of people had issues at 40k miles on those DI engines. I dont think many manufacturers tho are going to add a part that requires EVERYONE who buys it to empty is every 1-2k miles, the majority of people have a hard time remembering to change their oil every 10k miles, let alone get their hands 'dirty' and dump oil every month from a catch can. Just not something the masses would do so GM has the next best idea, w/ the 3 scavenge pumps and baffle system but its not perfect and I see what is left in the catch can.
^^^ Yep, those with the "If It Was Required GM Would Have Used" are often who don't check their oil or tire pressure as GM recommends. Some may not know or care that the engine must be up to temp AND running to check their oil. NO WAY EPA would allow a manufacturer to add something in the PCV system that needs dumping every 1000 to 2000 miles or it could cause emission issues! Heck the EPA in the early 1960's made manufacturers stop dumping crankcase "stuff' on the ground!
Also I recall when I dumped my "can" on my 2014 and 2017 C7 I put the spent oil in the container with a screw cap I used when changing oil! It got dumped when I changed engine oil at the local recycle center. Yep SC is a good state in that regard, we can dump about anything free. They have a large tank for oil etc. You can bring garbage free as well. What would the average C8 owner do with the oil collected, dump down the drain? In my case that would be really stuped as in our rural area we have a sceptic tank!
Do an "Advanced search" for catch cans across from at least the C5 Forums on. You will find MORE than anyone wants to read about the topic with posts consistently split on their worth.
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I've had two C4s and a C6 and did not consider a catch can. With quality gas (like Top Tier) and even just gasoline, with port injection or the Holley 850 carb on my street rod plenty of gas always washing the stuff away before in can bake on.
On my 1st three cars, a '41 Ford coupe I stuffed in an Olds engine, followed by a '50 Ford with a Flathead then my '56 Chevy small block, the crankcase "stuff" just dumped on the ground! (PCV systems didn't start until the early 1960's when the EPA said stop putting crankcase "stuff" in the air and collect and put in it the engine to burn with gas! )
Getting an early 2014 C7 with GM's 1st high performance DI engine (mine was built September 2013) and the coking issues BMW and Ferrari had with high performance DI engines I was concerned. Compared to a "grocery getter" DI, the valves in a high performance engine can get very hot. With zero gas, only air and PCV "stuff" going over the backs of the intake valves easy for some oil to bake on. Once it starts, leaves a surface for further build-up.
All car companies have gotten better and it appears to me GM has improved the C8 crankcase evacuation system so I won't consider using one.
02-19-2022, 12:25 PM
) Actually the situation is worse for Trackers or those using a lot of WOT. When the manifold vacuum is low, more crankcase oil is being pulled into the engine intake through the PCV system. In fact, the Catch Can system becomes more complex needing extra lines.
Yep, those with the "If It Was Required GM Would Have Used" are often who don't check their oil or tire pressure as GM recommends. Some may not know or care that the engine must be up to temp AND running to check their oil. NO WAY EPA would allow a manufacturer to add something in the PCV system that needs dumping every 1000 to 2000 miles or it could cause emission issues! Heck the EPA in the early 1960's made manufacturers stop dumping crankcase "stuff' on the ground!
