This is a copy of a reply to a customers questions regarding his C6 after a known tuner (one with no shop of his own) modified his PCV system & the potential damage this mod will do to the car. This is informational ONLY, and tuner does not matter, only the issues of modifying the crankcase ventilation system:

Understanding the GenIII, GenIV crankcase ventilation system & clearing up as much of the wrong info being given on the forums & in person by one known tuner that is eliminating it & the damage caused over time by this as well as the need for a proper catch can to prevent the oil mist from entering the intake manifold. Please note, there are several very good catch cans on the market that do an excellent job of preventing this problem, here are a couple that are popular on the Corvette Forum:



I’m referring to the capping off of the OEM system & running open hoses down to the ground from each valve cover.

OK, On the crankcase evac system: In the 30's/40's/50's cars had the crankcase ventilation system that this tuner uses. But it had one feature better...the intake of air was at the oil fill tube you see at the front of the old cars engine and it had an oiled steel wool filter & the down tube was one single tube that the venturi effect at speed would cause a suction (negative pressure) from this tube at the rear of the motor so the harmful vapors, caustic gasses, moisture, unburnt fuel, etc. would be evacuated or "flushed" from the crankcase where the heat from the motor at operating temperature would "flash off) these to a vapor. If they are not flushed out with filtered fresh air the vapors would re-condense inside the engine after cool-down & the droplets formed would drip back down into the oil & the damage done is slow, but over time irreversible. Remember, these motors rarely made it to 50k miles before needing rebuilt...part of the reason was less effective oil & other filters).

Now in the late 60's, the fresh air source evolved to include a filter & fitting in the air cleaner assembly (a small foam type that was to be replaced w/every oil change) and the vacuum (suction needed to flush the fresh air through the system) was sourced from the intake manifold vacuum (much more steady & effective because the old way would only pull air through while moving) and a PCV valve

to control the amount of vacuum & to act as a checkvalve to prevent back-flow from excess crankcase pressure or backfire from forcing oil mist into the intake where it contaminates the air charge & causes knock , lost power, and carbon build up on the pistons. Now look back & re-read.....the advancements of just adding filtered fresh air & steady vacuum had these motors going as much as 100,000 miles before needing rebuilds.

Now on to today’s where it is a system that is closed for emissions. The gasses that are drawn through the crankcase into the intake manifold are burnt through the combustion process & then the catalytic converters. Filtered fresh air is drawn from the throttle body front where it is filtered by the main air filter so no need for a secondary filter to get ignored & clogged. Then the fresh air enters the passenger side valve cover is pulled through the rockers, down the push rod valleys, through the heart of the crankcase where it flushes out all the harmful stuff mentioned earlier) , up the drivers side push rod valleys, through the drivers side rockers, out the rear of the drivers side valve cover, through the foam covered plastic hose around the rear of the motor, back up along the passenger side valve cover, to the PCV valve to the intake manifold & through the combustion process the amount of vacuum is regulated by the PCV valve. And a motor only pulls vacuum at an idle or low speed....at high RPM's the blow-by (yes, even the best motor has some) would push oil back into the intake if not for the checkvalve action of the PCV. This is where the catch can comes into play…..add the catch can to trap & condense the oil mist & vapor to prevent it from entering your intake. And with a FI application, adding a breather to allow for better filtered fresh air flow from the breather (which has a capacity of several times the OEM inlet) and it you have excessive crankcase pressure it would vent out the breather instead of into your throttle body & entering the intake from that passage.

Now on to an un-named tuners set-up: They eliminate all the PCV system & run 2 open hoses to hang near the ground. This does 2 things well, it prevents ANY oil from entering the intake, and it vents excess crankcase pressure down & away from the top of the motor where it makes a mess. But this is hardly worth a slow death to the motor as a result. As mentioned in the early days, a down tube provided the negative pressure to evac the gasses while at speed. This is called the "Venturi" effect. (swing a short hose around your head and hold your thumb over the end in your hand & feel the suction) With their set-up there is a hose run from each valve cover fitting to near the ground. At speed (even though they may be ending in the same place) one will pull more than the other, and the one with the least amount of pull will suck up dust, dirt, water, gravel, and who knows what DIRECTLY into your motor!!! And all the way through it! Just as pouring a cup of sand in the oil fill would do the same thing, but much slower. Following me here? They are doing this on theory & half thought only. The other harm is at idle or low speeds there is no vacuum pulling air through to flush out the harmful vapors & gasses!!! So when you shut your motor off, after it has cooled, you have all that crap re-condensing back into the motor. Just what all is in the crankcase while running? Water vapor #1 and unburnt fuel that dilutes the oil, and caustic gasses from the blow by....of which sulfuric acid is one main ingredient. So have you followed the science of this?

Hope this opened your eyes up a bit. Remember, I have been building performance & race motors since the early 70's, am a graduate of Reher Morrison Pro Stock engine building school, have run one of the winningest big$ bracket drag teams in the Eastern US for the past 7 years, have a shop of nothing but champion drag racers at the local, divisional, National, & World level. We race every single weekend somewhere in the country & we build & repair the motors that do this ourselves. These are motors costing $20k plus & making 1,000 hp NA. On our first C5 that currently has 176,000 miles on it, we started drag racing the vette when it had 25k miles on it & did not need to rebuild it until a nitrous "event" (screw-up) broke my #7 piston. This is a car raced every weekend at 2-3 events & many times doubled up w/2 drivers sharing. It has many times been driven 1,000 miles to a race, won or runnered up at many, and driven back. Do a Google search on RevXtreme drag race (spell rev xtreme several ways) and read the media coverage. It's easy to be convinced by some so and so who claims to know everything, but my whole team can back it up with knowledge, experience, qualification, accomplishments, and racing & testing & perfecting everything we do on a weekly basis.

 

Outstanding post, thank you for the information!

 

Thank you for your time and effort in casting some light on a poorly understood system.

 

In your opinion which of the catch cans out there are the best. If we use a catch can do we still need the PCV? If so where would we put it? Mine has long since been removed and I don't even remember where it goes!

 

Wow! That is one of the best reads on this forum. Concise, common sense explaination. Thank you!

 

Our can has an integrated PCV valve into it, and yes it is a must. Without the PCV valve the vacuum is uncontrolled & at high RPM's you need the check-valve feature to prevent back-flow.

As far as the catch cans, it depends on your application. Mike Norris has probably the nicest looking & trick construction. I'm biased toward our due to the size & functionality of it. The main thing is to have one with good capacity for the condensation needed to trap the oil vapors & mist & that it is baffeled or diverted so to not have a direct patch from the inlet to the outlet. Just a "can" will not be very effective, but it is better than no device.

 

Can your can be used in conjunction with the updated "truck" PCV valve (factory location) that has a smaller restrictive opening and no check valve?

Thank you,

Dave Dugger

 

I know PCV valves need to be replaced after time. How does the integrated one fair against replacement?

 

How about a breather on the pass valve cover and a air/oil separator with a vacuum pump on the driver side

 

Nice post! Very informational and helps out alot

 

Thanks for the information. I am going to check out your cans. I have the home depot filter but am not comfortable with its functionality. Plus I have no PCV which is a problem.

 

Does your catch can come with a detailed instruction sheet?

 

Yes, with pictures & optional application instructions as well.

 

Good post Tracy. I never ceases to amaze me that someone would suggest hanging wide open hoses in the first place and that a customer would actually allow it to be done to their car.

Heck, I am not even a fan of having an open breather on a daily driver car due to the fumes it causes. A properly working engine will only require and in-line catch can to catch a minimal amountof oil over time.

If it is pushing oil bad enought to actually need a breather or hang hoses to keep oil out of the intake, something else is very wrong.

By the way, mine is better

Mike Norris

 

Gotta agree on the deeper problems if a catch can dosen't do it...and a breather is rarely needed (track or off road mainly).

The world is full of sheep looking for a shepard to lead them. God Bless

 

Some good info in here... Im trying to decide (research) what I want to do when I re-install my motor. I have a head/cam LS1 and get a good deal of oil in my FAST 90. I have the LS6 vally cover. But it doesnt seem to stop it. I isntalled a home brew home depot catch can, but it seems to get alittle oil in it, then let it all through.

I was going to try running a breather(s). Im not worried about oil smell, or the possibility of alittle oil film on things, or havnig to change my oil alittle sooner. I AM worried if its going to destroy my motor however. The car is mostly a street car and pulls daily driver duty pretty regularily. Im not sure I follow the whole "if your motor is gettign oil in the intake there is something else wrong". Because Ive heard of cars off the lot getting oil in there.

I havent seen the oil catch can posted in here...except for Mike Norris's. But Im curious...if running the catch can, why would you want to put a breather on the oil fill cap like in the pictures for the revextreme set up??? Im still unsure what to do about the issue. Guess Ill keep an eye on this and see what additional info pops up.

J.

 

Breather is usually only used on FI setups & for those that run at high RPM's alot....other wise the stock fresh air source is fine & meets emmissions.

 

Mike, we should talk about this with the APS going on, eh?

Great thread!!!

 

Incredible post here. I did not understand how the PCV system worked until this post. I knew its purpose but not how it functioned. Excellent job.

One question though: Should there be any concern to not running a catch can? I have never really had a second thought about changing out my PCV valve to a catch can but I see plenty of people do it. Is there really a negative affect to running the stock PCV system on a minor mod car? Sounds like someone with full bolt-ons or more should be more worried about it.

 

Really good post ! I thought that the PCV system was installed mainly to recycle all the harmfull vapors created by the engine back into the intake . That and the EPA makes it manditory for production vehicles since those vapors harm the enviroment and ozone .
I had deleted mine and put in breathers just because of oil and hot gasses in the intake even after a catch can . Plus the fact the air is not metered by the MAF thus not calibrated into the car's computer . Just do a search , the PCV has been long debated and everyone comes to their own conlcusions .
Nice looking catch can btw .