13 SRT8 no catch can

Fuzzymers said:

I’ve had numerous intake manifolds off that drip in oil to prove a catch can is extremely worthwhile. My TVS2300 GTO, NA GTO, Challenger, and Charger all have catch cans. They each catch roughly the same amount of oil after the same miles driven.

Oil vapor coating the intake manifold and the back of the valves isn’t a great thing and manufacturers know it. They don’t care as they are in the business of selling new cars; not the longevity of them past the warranty. The PCV systems are meant to control emissions by burning crankcase vapors. That vapor also reduces the effective octane rating of the gas charge into the combustion chamber which can potentially cause detonation/knock; especially as the mileage increases.

Bottom-line: They work and are beneficial for all vehicles.

Click to expand...

Yes, engines lift oil. They get behind the valves. Yes, NA engines lift oil and oil does in fact reduce the octane rating of the combustion chamber. Context, though, is key here. Do you know how much oil soot it takes to gum up a valve? If you're just talking oil deposits, on an engine running correctly, it would take a half million miles or more to build up any amount of appreciable deposits. The majority of these cars will never see 200,000 miles. Now, the real killer on valve deposits is over-rich running engines and/or engines running with a misfire caused by mechanical issues, bad gas, etc. You can create more deposits in a month with a bad or poorly gapped spark plug than you can over a lifetime of normal oil deposits.

NA engines can lift a little oil via the dirty side of the PCV. I had a catch can on a 392 T/A for a couple of years. In that time, the J&L oil separator caught maybe a 1/4 cup of oil over 2 years of daily use (28k miles). Boosted engines can lift a lot. On my Redeye, I can catch a teaspoon of oil every time I go WOT for an extended period. I can fill a catch can in 5,000 miles. This is caused by many times elevated crankcase pressures vs what you see in an NA engine. Boosted engines CAN lift enough oil to negatively impact the octane rating in the combustion chamber. No stock Mopar NA engine can. The 392 has a 72.4cc combustion chamber volume. To negatively impact performance to the point you could feel/notice it, you'd need about a 5% total volume of oil in the combustion chamber... which comes out to about 0.9 ounces of oil present in the entirety of the top end of the engine on the ignition stroke to achieve performance degradation. This is more than what most 392's see in 3 months of use in the bottom of the catch can. In comparison, my Redeye can lift this much oil in 1 WOT pull from 80-150mph. In my case, while it's possible that I could get enough to cause the car to briefly pull timing at the top end of 3rd gear, it's still mathematically remote that it'll lift enough in a finite period of time to cause the PCM to pull timing.

With the 392, it's impossible for it to lift enough oil to adversely impact the octane rating in the combustion chamber. This is doubly true for the 5.7L.

With older engines, even those with high miles, they'll have valve deposits, but almost all appreciable deposits are caused by unspent fuel or additives, not oil. For an engine that has ran perfectly for 50k miles or more, you might have 1-2 mils of carbon coating on the back of the valve. It's thin enough to easily scrape clean with the back of your fingernail. On almost any internal combustion engine, it would take millions of miles before oil deposits gummed up a valve on an engine running normally. This is because oil in the dirty side of the PCV is kept in aerosol form (vapor). It typically doesn't stop or cling to anything and passes harmlessly out the exhaust. When you DO see visible oil, that's from condensation caused AFTER you turn the engine off. Over time, you'll see what looks like tiny pools of oil in the throttle body, maybe in the intake runners. Once that oil vapor condenses, it'll usually stick in there and hang out. Heavier materials are generally pushed to the outside of the runners, for example, and will stay long-term and build up over time, giving an untrained eye that the car is lifting a bunch of oil... but that's usually months or years worth of accumulation.

Catch cans are then a bit of a self fulfilling scam of sorts. They put a catalyst in the PCV system that forces the oil aerosol to condense and fall into the catch can. Thus, removing "harmful" oil. Without that catch can though, that would have never condensed into liquid oil at any time during the engine's operation. Low volumes of oil aerosol doesn't gum up anything. Now, under very high pressure (aka compression stroke in the combustion chamber), it can force that aerosol into a liquid, briefly. This is where, again, boosted engines running much higher pressures caused by forced induction can benefit from a catch can. They do lift more oil and their internal combustion chamber pressures are much higher. But, as soon as the spark fires and at the end of the power stroke, the exhaust valves open and that oil is turned back into an aerosol. At no point is there ever any liquid oil in the cylinder on the intake or exhaust stroke if the engine is running correctly... so there's not any oil that's gumming up any valve seats. Almost all gunk buildup is entirely caused by unspent fuel and additive deposits.

Thus, a catch can does well at solving a problem that doesn't exist on 99% of all cars on the road. Unless the car is running high boost levels, the engine is just not going to lift enough oil to ever cause an issue.

That being said, a catch can won't hurt anything if it's used. Folks like to say it's peace of mind and all, but the reality is pretty simple. They don't do anything on NA cars. Nothing that the engine already doesn't do for itself. The only damage done is the $150 or so a person pays for the catch can. I'm not going to sit here and tell folks to not get one. If they want one, it's not going to hurt anything. You just don't get much benefit either, other than it looks like they added a mod to the car for when they go to Cars and Coffee.