madrob2020

It's too funny but really sad. We have 3 or 4 folks on here that have never "lost" an argument or admitted they "might" be wrong. They post 6,7, 8 or more times trying to prove "I'm right, you're wrong". Topic doesn't matter, they just like butting heads. Could be be tranny, best shifter, best gas, best**** whatever. Just check out the # of posts under their user name & you can tell who they are. I seldom chime in but do like to read their "opinion" for a laugh. They do resort to name calling sometimes which is a hoot. Now I'm probably gonna get torched-oh well, it'll be funny also.

Foosh

I don't think it's harsh criticism, and I don't disagree with your other points either. In fact, we agree more than disagree. I'm just losing patience with those who claim catch cans are a solution to valve coking in DI engines, while posting movie clips from "My Cousin Vinny" and cartoons of ostriches as if that makes some kind of compelling point. It's comical.

Where we do disagree is that I don't think there's enough collected to cause issues in the other areas you mentioned. Obviously, a small amount of oil sitting in the bottom of a can is going to start getting milky, sludgy, and gnarly exposed to air and moisture for a considerable period of time. Posting sensational pictures of that doesn't prove anything, but definitely generates an internet reaction. That sells a lot of cans for vendors.

I trust science and engineering data. Show me solid evidence, and I'll believe it, but I've yet to see it. Every time this subject comes up on the forum the same non-sensical movie clips, pictures, and cartoons get posted as insults to those who disagree without any scientific or engineering evidence, just amateur speculation. The only things I've seen on this forum approaching solid evidence are a few pictures from very high mileage LT engines without catch cans showing minimal valve coking, as well as the fact that you never see any reports of valve coking performance problems on LT or recent GM DI engines in general. A lot of these engines are well over 100K miles.

SLOWRYDE

Yeah, I don't have any engineering data or scientific evidence to support any of my notions. I do have experience cleaning this crap out of the intakes and off the throttle bodies of numerous LS bases engines and I just didn't like the idea of it being ingested, even if I couldn't prove performance degradation. Posting pics really isn't about sensationalism but giving the owners inexperienced with what these devices collect a visual representation. Nothing more.

At the end of the day I'm out $200. My intake and throttle body stays clean and I sleep well. Good enough for me. Your mileage will vary.

PatternDayTrader

There is no mystery about the coking issue.
Oil coking on the valve head comes from the very small amount of oil that gets past the valve guides.
A catch can wont change that.

JerryU

As you state, I also have never said that a "catch can" solves the coking problem in DI engines fully or just how much it helps. But condensing some of the oil vapors, collecting and dumping it frequently provides some reduction. Cheap insurance!

I post my fun pics to point out the closed minded view that PCV "stuff" going into the intake may not cause 'coking' on the intake valves and it does not magically go away in a GM DI engine, in fact it is worse. It has occurred since the EPA stopped crackcase stuff from being dumped in the air in the 1960s. It was minimized when we had port injection and carburetors by using gasoline and gas with Top Tier and other "cleaning additives" that washed it away. With DI there is no more gasoline passing though the intake and over the valves!

DETAILS:
I am not going to repeat the 19 pages of info in my PDF (even I'd roll my eyes) but these are a few comments that are documented with references for some of those ~900 silent majority who have viewed this Thread versus the few of us that have posted"

A 2014 magazine article quotes two GM engineers who were discussing the LT4 with the author Brandan Gillogly in a two day session. John Rydzweski, Assistant Chief Engineer for Small Block V 8’s was one of the two engineers.
This is a quote by the author NOT one of the GM engineers.
“A little bit of oil on a port-injection engine can help lubricate valves, but because the Gen 5 V8’s (all C7’s as the LT1) are Direct Injected, there’s no fuel washing the back of the intake valve. That means oil in the PCV system can end up sticking to the back of the hot intake valves impeding airflow and eventually preventing the valves from seating properly.”

After being criticized saying that was the author, I emailed him and he replied stating those topics came up in his two day session. He is a very good writer and has many excellent automotive articles. You decide!

This is what Tadge said in forum posts:
“Granted, deposit formation on SIDI engine intake valves is greater than what is seen with PFI engines, but the Gen 5 engines are typical for SIDI engines, and in fact better than other SIDI engines we have benchmarked. “

IMO that does not say it's no problem. In fact it goes on to say it is a cosmetic issue!

This is from a Tadge post answering a question of why the Vette does not have the “improved PCV system used in the Camaro LT engines."
“In a "Catch-Can" systems that do not have a drain back path for separated oil run the risk of poor oil pressure performance over time as oil is removed from the lube system."

First note Tadge says it's oil! I interpret his statement to mean “if you don’t dump the oil from the "can" you can have problems. Those that are not DIY folks may not empty the can frequently that could result in a problem." I agree.

Frankly I don't mind debating issues with Foosh in this open forum as some of the silent majority may benefit from the dialog. He is often right on many subjects, just not all! I also have fun writing and post pics to help those who read them get though all those words!

Frosty

If the GM engineers thought a catch can was needed, wouldn't they have included one in the design?

Red C8 of Jax

Most definitely. This subject has been discussed ad nauseam.

JerryU

The majority of the oil and oil mist in the crankcase is caused by oil leaving the rod and and main sleeve bearings and hitting spinning crack. The LT engines also include oil "squirters" that direct oil to the hot pistons and cylinder walls. Some of the mist particles hitting those hot pistons and cylinder walls oxidize.

A quality catch can includes some stainless ribbon that condenses some of that mist and forms droplets that fall into the can. It is then removed.

The reason GM and other manufacturers don't add one is most folks don't even check their oil level as recommended. Those none DIY folks would never take it apart to empty and then where would they dump it? Down the drain? EPA would not be happy!

In fact from my observation GM has improved the dry sump system to keep some of that "stuff" in the crackcase and drain some of it back to the valve covers etc. Many more lines from the Grand Sport dry sump tank to the engine. I'm collecting about 2/3 less "stuff" in my Grand Sport than in my 2014 Z51 catch can.

PatternDayTrader

I cant buy into this hypothesis, as it fails to address two separate realities that can observed by anyone, with or without an engineering degree.

The first; oil coking does not seem to accumulate in the intake ports or around the valve seat. The second; some valves may have considerably more accumulated coke than other valves from the same engine.

Knowing this, you would expect pcv oil to be evenly distributed (roughly) throughout the intake ports in aggregate, and through each port individually. In other words, if oil coke came from pcv oil, then it would accumulate everywhere in the intake port and not just on the valve, and accumulation would be roughly even amongst each port and each valve. Neither of which seem to be true, and neither of which are explained with the pcv oil hypothesis.

PatternDayTrader

I agree w everything you just said.
The oil mist directed at the pistons is very likely contributing to why there is quite a lot of pcv oil.

JerryU

Oil may be distributed but coking requires baking the "stuff" onto the surface. In addition at WOT expect oil will be carried into the combustion chamber but it has to pass the very hot intake valves. Since I ordered my 2014 Z51 many months before the first production had lots of time to research the DI coking issue. Below are some details:

DETAILS:
First, the oil that creates "coking" bakes on the hot intake valves not on the intake manifold walls. My first concern about DI came from Ferrari and BMW who had high performance engines with DI several years before the LT1. They have 4 valves per cylinder, two intakes. The intake valve is exposed to the ~2500 F combustion gases. It has to conduct that heat away as the center of the valve can reach ~1300 to 1400 degrees F. ~75% goes through the valve seat to the cooler cylinder head, the remainder though the valve stem and the incoming air. The outer edge in contact with the cylinder valve seat can reach ~1000 degrees at max power. That is far more than enough to cause oil and stuff to bake and form carbon deposits.

In the much larger intake valves in an LT1 heat must flow for a longer distance from the center to the valve seat. As the valve gets larger there is less area around the valve than the hot center area. (To crunch some numbers a 1 1/2 diameter Ferrari valve has 66% of the perimeter to center area and a 2 inch Vette valve has only 50%.)

And Ferrari and BMW were reporting problems and recommending walnut shell blasting as a solution! In fairness to GM they have done a great job managing the problem in the LT DI motors but some coking still exists.


Side Bar:
This is a fun valve related story (at least to me!)

When my Mother-in-law was in a retirement facility in FL she had a friend who was also originally from NE Ohio. George Sanborn had owned a number of auto parts stores. He relayed a story about looking at an exhaust valve that Charley Thomson (of TRW Thompson Ramo Woolridge) operating on a running engine! They cut a hole in the exhaust manifold and were testing valve materials. In his day Sanborn was selling many engine parts and rebuilding engines.

I recently bought some NOS valves for the R2800 one of 18 cylinder radial engine of WWII fame I have in my man cave. It was used in the Corsair fighter plane.

You can see on the box in the pic below it was made by Thomson Products in Cleveland OH before TRW was formed!

Note the 3 inch intake and 2 1/2 inch sodium cooled exhaust valve! The Pratt Whitney engineers increased the HP of that engine from 1800 before the war to 2800 at the end! But if you used the 2800 hp in a dog fight to save your life and you survived the engine had to be rebuilt! Those were dedicated knowledgeable engineers of the day!

PatternDayTrader

Even if I give you accumulation on the valve heads only, that wouldn't explain how some valves can have lots of accumulation while others (in the very same engine) may be clean.
Don't get me wrong here, I'm not anti "catch can", and I would run one if I had a good reason; its just that oil coking on the intake valve, is not a good reason for me.

JerryU

Don't have an answer but air flow is funny and not intuitive. Today there are a number of software programs that can simulate what is occurring. In AA/Fuel dragsters and even ProStock cars the distribution of air and fuel is not uniform. Reading plugs and putting thermocouples in each exhaust pipe is still common to fine tune combustion to maximize power. Recall in Dragsters they had to move the big 871 blowers forward quit a bit to get more uniform air flow into the cylinders. Would assume since the PCV inlet enters the LT1 manifold on one side toward the front of the engine it could account for some variation.

This is a fun video of the fuel being pumped in one cylinder of a AA/Fuel Draster. Saw this at the museum at Pomona CA Raceway.

Now get the air balanced to match! It starts at an idle rate than under power. Only have to last less than 4 seconds! :lol

davepl

If it was required to meet emissions, yes. And I don't just mean oil emissions, it might have been required, let's say, to keep octane-killing oil out of the intake stream with our compression ratio, or for some other reason.

But they didn't. And then they slapped a 5 year, 100,000 mile warranty on it. Good enough for me.

PatternDayTrader

Dang ... crazy video.
Not much atomization going on there...

JerryU

^^

Don't need much with 98% Nitromethane as it caries it's own oxygen! And that 80 psi blower pressure (not in the fuel demo) creates some as well.

PatternDayTrader

Well one thing is for sure, its no wonder why those things blow up in such spectacular fashion, whenever there's a misfire.

Highplains

I certainly do not claim to be an expert on catch cans or whether they are needed or not. It would seem to me that after it's all said and done, the worst thing that could happen in having one is nothing. That being said, I would assume you have $150 to pay for it and the ability to take it out if your car is going to a GM dealer for warranty work.

JerryU

^^^
TRUE. However I'm confident enough that my single outlet can is installed properly and is not causing a problem.

That said, the ~6 inch long OEM PCV hose is in my rear compartment and it would take <10 minutes to pull off the two Can hose and push it on the barbs from the PCV valve and the port to the engine! One nut holds the can on a stud!

Took me less time when I removed it from the 2014 Z51 as I had a 3/8 inch drive ratchet and socket to remove the nut! Install on the Grand Sport did not take much longer!

CADbrian

Of course searching for useful information was my first step, but as Foosh points out, there is a lot of irrelevant data, and having sorted through a fair amount of it I decided to post.

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