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I used to venture the camaro5 forums a few years ago and there is a wealth of knowledge over there about catch cans. This below was a post that I read a few years ago that really stuck to me so I thought it would be prudent to share. It is by a knowledgeable engine builder that is well respected in the ranks. I had a catch can on my camaro and drain it every oil change. I always got about 3-4oz of oil in there. It is possible that the LS3 engines have more blow by but the information still applies.

The biggest thing is that I got out of it was that oil vapors ingested into the intake lowers the octane of the fuel.

The issues of oil ingestion into the intake air charge

You want NO oil in the intake air charge, only air & fuel (and the combustable combustion byproducts that enter the crankcase via blow-by). Any oil reduces the amount of usable octaine and also causes detonation. Both result in less energy released per explosive event and detonation is destructive. The cars today have very effective knock sensors so you will never hear the "marble rattle" of detonation before the ECU pulls timing to eliminate it, but when doing so you loose power & fuel economy.

The long term harmful effects are the carbon & "gunk" buildup on the valve tulips, piston tops, ring lands, and combustion chamber.

Any time build up occurs the volumetric efficiency of the port designs and flow suffers and is negatively affected. The burn pattern quench area, etc. all cease to work as designed. Then you have the deposits causing stuck rings and when the hard abrasive carbon particles/deposits break loose some are forced past the rings and cause scoring and acellerated wear.

Catch cans. Most on the market are just empty cans with to fittings added and even though many look awesome, only a handfull are actually truely effective in trapping all or nearly all the oil before it can enter the intake air charge.

Even a beer can will trap oil if two fittings are added (yes, we tested one as a joke...and it worked as well as most cans sold today).

Most cans are far to small so the velocity, or speed of the flow through them pulls most oil right through and out into the intake. (take a small hose, add a teaspoon of water, and blow lightly. ALL the water is forced out. Now take a 3/4" heater hose and do the water or amost none will be forced through).

Then, most have the outlet & inlet close to each other so the crankcase gasses never have a chance to cool, condense, and the oil allowed to fall out of suspension. I see some of the nicest looking and quality in appearance do a poor job at best as they have coalescing filter materila in both the inlet & outlet so as long as the motor is running, and there is flow through only the lrgest drops get caught, the rest just pulls right through the can and into the intake. These catch oil when the motor is off and there is no flow through as the filter media willdrip down what has neen saturated so when you open or drian them you see oil and assume it works. The goal is to trap ALL or nearly all the oil to prevent the issues outlined above.

I should mention, after installing the RX can we see 1-3 mpg improvement over stock.

Now, some will ask, "why not just delete the PCV and run breathers"? This is where we find the PCV system is the most misunderstood system on cars today and almost NO techs today, or aftermarket performance shops/vendors understand. First, most beleive it is just to releive excess crankcase pressure. This is true, but it does far more. Every internal combustion engine has a small amount of blow-by even if sealed well. This blow-by consists of unburnt fuel, water vapor,carbon particles (very abrasive), sulfer, and other compounds that are harmfull to the motor and the PCV system evacuates, or "flushes" these compounds out while they are still suspended in the gasses. If they are NOT evacuated before the enginne is shut down and cooled, they condense and mix into the oil. The moost damaging are the fuel as it dilutes the oil, the carbon particles (to small for the oil filter to remove) as they are very abbrasive, and the water & sulfur, and other compounds mix to form sulfuric acid. An oil analysis will show the levels of these compounds as well as other metals from wear. The sulfuric acid after it reaches a certain PPM will begin to etch the bearing & journals surfaces leading to premature wear and possible failure. The water causes corrosion.

This is a condensed explanation but one that most can follow and understand. Techs the last few generations have been trained only to diagnose and swap parts...not how these systems work so we are "dumbing down" service techs to just be flat-rate parts changers so very few dealer service departments know any of this any more.

Visualize how a crankcase is evacuated properly. On the 3.6, metered,filtered fresh air enters the rear of the drivers side valve cover, trvels around the valve train, down the oil returns, through the crankcase, (all the time pulling and flushing these compounds with it), up the passenger side past the valve train and out the rear of the passenger side valve cover where it is drawn into the intake manifold and is burned in the combustion chamber and further in the cats.

A proper functioning catchcan is simply plumbed inline between the passenger side valve cover oulet and the center of the intake manifold so it can condense and trap the oil before it enters the intake air charge. They need to be emptied every oil change, and the oil is NOT to be resued as it is full of contaminates. Dispose of with the rest of the drain oil properly.

benefits from catch can - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums -
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