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The problem is there is no proof they actually improve anything on GM Direct Injected Engines since there are few reports of GM DI engines suffering from valve coking even though GM has put millions of engines on the road over the last 13 years.
Sold the one on the 2019 C7 I had for $100.00 and got this one for my new C8 for less than $240.00 Shipped, put it on yesterday at less than 400 miles.
lol -- the theory is that recycled fumes and oil vapor on a direct injected car will cake the valves due to no fuel vapor stream to help "clean" them. The idea of the can is to add an additional layer of separation to keep as much out of the intake paths as possible.
The problem is there is no proof they actually improve anything on GM Direct Injected Engines since there are few reports of GM DI engines suffering from valve coking even though GM has put millions of engines on the road over the last 13 years.
lol -- the theory is that recycled fumes and oil vapor on a direct injected car will cake the valves due to no fuel vapor stream to help "clean" them. The idea of the can is to add an additional layer of separation to keep as much out of the intake paths as possible.
Thanks for spending the time to do the explanation.
I'll let all of you more experienced do the commentary on its value.
Ah yes, CATCH CANS... for more about catch cans and the debate involved, one can go to at least the past three Corvette model Forums and do an "Advanced Search." One will find more threads, posts, and opinions than almost imaginable.
Post up and let us know if the can actually traps anything. The C7 has a built in oil separator from the factory that automatically drains back into the oil pan. I'm not sure about the C8 yet, but it must have something similar.
The 2 C7's I owned had a small amount of oil in the catch can between oil changes. I am going to inspect it before the first oil change. Most likely it is going to catch a small amount of oil that would of been ingested into the intake.
Post up and let us know if the can actually traps anything. The C7 has a built in oil separator from the factory that automatically drains back into the oil pan. I'm not sure about the C8 yet, but it must have something similar.
The C8 has a oil separator under the intake manifold.
On my C6Z, if the car was only driven reasonably on the street no need for a catch can in the PCV circuit, virtually no collection in 2-3000 miles, even steady running at 150 MPH in 5th for 90 miles.
On a road course running 4000-7000 rpm and then heavy braking and significant vacuum, I get 4 ounces per day ( 1 hr+ of track time).
The problem is there is no proof they actually improve anything on GM Direct Injected Engines since there are few reports of GM DI engines suffering from valve coking even though GM has put millions of engines on the road over the last 13 years.
Bill
There were also multiple reports on CF of C7 LT1 engines (no catch cans installed), over 100K miles, in for service for valve spring or related issues, with mechanics reporting no significant valve carbon deposits, as reported by the servicing mechanics. Had it been present, I'm sure they would have been happy to make some additional money on a walnut shell valve blast.
As you say, there is no evidence that GM LT engines suffer from the DI valve contamination issues present on other makes of DI gasoline engines, and the LT2 has additional countermeasures in the place (another oil separator) to ensure it's not an issue. The small amount of oil collected by those who have installed catch cans on LT1s simply isn't enough to cause problematic carbon deposits on valves.
You are 100% correct, there is no evidence of a problem on LT1s, and even more reason to believe LT2s will be no problem.
On my C6Z, if the car was only driven reasonably on the street no need for a catch can in the PCV circuit, virtually no collection in 2-3000 miles, even steady running at 150 MPH in 5th for 90 miles.
On a road course running 4000-7000 rpm and then heavy braking and significant vacuum, I get 4 ounces per day ( 1 hr+ of track time).
Where is this 90 mile road you speak of? Asking for a friend
No C6 engines (or earlier) were direct injection (DI), thus the fuel injection systems of that day (port injection), coupled with Top Tier™ fuel, kept valves washed. First DI engine in Corvette was the LT1 in C7.
I've run 13 events, 10 in the 150 MPH class. Best finish 2nd in class with a time variance of .0146 seconds against a 36 minute flat target time, hand timed, solo. Lost by .0011 seconds, less than 3 inches over 90 miles at 150 MPH average. Many of my runs were within 1/2 second of my target time.
They run an Open Road Race in TX called Big Bend, not quite as fast, but still a fun event.
Last edited by AzDave47; Sep 20, 2020 at 08:40 PM.
It’s not worth voiding your warranty over something that probably isn’t significantly more effective than the LT2’s stock oil separation system.
I do wish they had added port injection on top of the DI in the LT2. Toyota always combines the two so that the valves get sprayed clean by the port injectors. Otherwise there is premature valve stem and guide wear due to carbon buildup, maybe not at 60k miles but Toyota is looking ahead to 200k miles.
Anyone who doubts this can look at photos of LT1 intake valves after 20k miles or so. There’s a lot of hard abrasive carbon deposits already but GM bean counters don’t care because the engine will be fine for the warranty period.
The introduction of DI in the 2014 C7 was GM’s first venture WITH a high performance engine where large intake valves get very hot. BMW and Ferrari (among others) were ahead of GM in high performcne DI engines had significant problems with build-up of burnt on carbon deposits on some engine intake valve backs. Both had no simple solution. Some folks had their intake valve backs "walnut blasted" to remove what is called “Coking.”
Concerned, that the science in GM engines was no different so installed and inexpensive Catch Can that was well designed and condensed the oil vapor coming from the crackcase into the intake manifold via the PCV system. Found I was collecting ~1oz/1000 miles in the can (non Tracking.) That was 1oz “caught” not Coked the back of the intake valves. BUT the “can” had to be emptied or could cause problems. Heck GM (and others) have a hard time getting folks to check the oil level when they suggest, no way would they add a “can.” If they did where were folks supposed to “dump the consents?” Down the drain? Nope- not good!
When I got my Grand Sport had removed the “Can” from my 2014 Z51 and planned to install but carefully evaluated the "New, much more complex PCV system GM developed for later Dry Sumps.” Wanted to be sure "I did no harm." Many more lines going many more places! Checked out OK so I did. Yep GM made a significant improvement, collected half the amount ~1/2 oz/1000 miles. Looked like no longer needed especially if not Tracing or had a supercharger.
Chuckle at the “coking deniers” who refuse to admit GM spent a lot of time and money engineering a “better” system for 2016/2017 systems since there was "NO PROBLEM" with the earlier dry sumps.
May depend on how OCD you are! Some get concerned about fingerprints when they close their door! I don’t car about them, come off when I wash it. BUT I assembled the Olds engine in my 1st car, was a sponsor of Richard Petty for >15 yeas and saw the inside of their engines and more recently assembled the 8.2 Liter BB from some 30 boxes for my street rod. Saw those spotless intake valves and passages designed for maximum air flow. The build-up on the valves has me much more concerned that fingerprints on the car body! No, the engine won’t fail but it’s NOT helping performance! (PS: is a published article where the GM small block engineers said what could happen if “coking” became excessive, especially an issue with the LT4.)
Since GM spent a lot of engineering time and effort improving the newer C7 dry sump PVC system (for what some think was a non existant problem ) they no doubt went even further with the LT2 and most of the vapor from the crackcase is condensing (as the “Can" Does) and it drains back to the crackcase! Will not consider adding one on my C8.
Here is a picture history for those that don’t read more than 280 characters!
Why Coking Was Not An Issue With Port Injection IF You Used Gas With Additives. If NOT IT Could Occur. Lower Pic is Ad For Using Top Tier Gas to Reduce Coking That Could Occur With Even Port Injection With Gas NOT Having Cleaning Additives. Guess For Some Top Tier is just BS!
Pic Far Right a BMW DI Valve "Coked" Needed Walnut Shell Blasting GM Spent Lots of Engineering Tiime and Money Developing a Better PVC System for New Dry Sump Systems in 2016/2017. All that Engineering Time and Effort to Fix A Non Existant Issue in 2014/2105 Dry Sumps! Yep Built the Engine in My 1st Car in 1959 and This Recent 8.2 Liter BB for My Street Rod. Saw Many, Smooth, Clean Intake Passages in Engines In-Between! For Some It's Like Sweeping Dirt Under The Rug! Since they Can't See It- It's a Non Issue!
In a few words, compared to Jerry's stock dissertation and cute cartoons, which have nothing to do with data from Corvettes: No one here (and certainly not me) has denied that there have been valve coking issues on a number of DI gasoline engines. I had the problem in an Audi, which needed a walnut shell cleaning. Thus I 100% understand it CAN be a problem.
The point, which always whiffs right by Jerry in dozens of threads here over several years, is that there is no available evidence of significant valve coking in LT1 engines in C7s. If those data exist, no one on CF has been able to find it. Thus, there no reason to suspect there will be a problem in LT2 engines.
There is also no available evidence that catch cans solve the problemin DI engines with a history of valve coking issues.
