PCV/Catch Can/Crank Pressure
Back in the day...around 1966 BTH ( Before Tree Huggers) for me anyway, when I was starting to wrench .....pollution control wasn't a consideration. Nor was gas mileage. Pretty much we just sat around thinking of how to go fast and get laid. Yup...that was pretty much it. Today lots of things has changed. We still want to go fast and get laid....but the internal combustion engine has become so efficient and regulated we have had to learn new "tricks" to enable us to go fast within the confines of the new regulated pollution control engineering restrictions laid on us gearheads. Now before anybody jumps up and calls me a polluter let me just say a tuned high performance engine today is a 1000 times less a polluter than the old engines of yesteryear. As we modify todays engines...yes we will vent crank gases to the atmosphere....but it is so insignificant it hardly can be argued we are polluting. So blow me I am in a foul mood anyway as that damn spotted owl I had for breakfast is making me fart something fierce. So blow me in advance.
OK...I'll start at the start.
The internal combustion engine basics hasn't changed hardly at all since the first one was fired up over a 100 years ago. Piston goes up and down and valves open....fuel is mixed with air....a spark occurs and kaboom...you got power. We all know the air/fuel is compressed by the piston going up in the cylinder...and that is cool....I'm going to speak to the piston going down the cylinder.....that very action produces pressure back into the crank. With back pressure all kinds of things happen. None of them good. Your oil gets polluted with fuel and burnt gases from the blow-by past the rings.....anybody don't think any blow by gets past your rings is fooling themselves. This is where oil sludge came from back in the day that gets blamed on Pennzoil :) It wasn't the oil it was the fuel/burnt gases causing the oil to break down and sludge folks. Also these old engines leaked oil like a son of a bitch as the crank pressure would find the easiest route out of the engine...and that was usually around any gasket or seal :) So the rocket scientist designed what we used to call drop lines from the crank (usually the valve covers)...these were 3/8"-1/2" rubber hose that ran from the valve covers and hung down below the car. The idea was the air passing under the car would create a vacuum and draw out the crank gases and allow pressure an escape route versus out your rear main seal :) These hoses would get clogged up with bugs and stuff and you would have to blow them out or your entire car would smell like gas/oil.....My girlfriend back then would suck them out for me as she could suck start a diesel truck and that worked out well for both of us...I digress......
Well folks started dropping dead on the sidewalks of Los Angelas and the tree huggers union was formed. They raised hell beat pots and pans together and sacrificed chickens...so the rocket scientist come up with what we know today as the PCV. That would be Positive Crankcase Ventilation. They now routed the vent hose back into the carburetor. Brilliant! Guess what? When you do that you have one helluva drop in power. Why? Pay attention here.....because now you have oil/burnt gases being mixed with fresh air/fuel....and that causes significant detonation as your air/fuel mix is now diluted...so to fix that you have to pull a shitload of timing (where your plug fires in relation to the location of your piston to top dead center).....and this of course significantly reduced the amount of hydrocarbons being vented into the atmosphere as the gases were now being burnt twice.....problem with this is where does the crank pressure go? Well....it seeped out the intake manifold...the rear main seal...every gasket you could think of....talk to any "old guy" and he will confirm we leaked oil like Paris Hilton dropping money on Rodeo Drive. So the rocket scientist went back and created the "Smog Pump"...WTF is a smog pump you ask? Well some where mechanical and some were electrical...but both did the same thing....they "sucked" the air out of the crank like a vacuum cleaner and routed it back into the carburetor. Brilliant! Look at the horsepower drop around the early 70's across the board. This is why. Of course we stripped all this shit off :) But now days you cant do that shit...so here we are. Huge changes has occurred in the pollution control devices/methodologies since the early 70's....but the basics haven't changed all that much.....a new 2007 LSX motor is routing crankcase burnt gasses/oil back into the intake and here is where I'll get started on our LS1's and 2's specific. I know I blew by the above but hopefully the history will help a fella understand what it is we are doing here and why.
Well the first thing a guy can realize is by getting the oil mist out of his/her air/fuel is a good thing as todays LSX ECM will pull timing if the knock retard sensors go off. So from the factory they have calibrated the tune to compensate for this oil mist/burnt gases being re-introduced back into the air/fuel mixture. So when you go get a custom tune the tuner can only give you so much timing ( closer to top dead center the more you compress your mixture the more power you make) without getting the dreaded knock sensor going off and instantly reducing timing and you go slow again.....so you have to eliminate the oil mist and then your tuner can give you more timing and not set off the knock retard sensors :) Brilliant. How do I do that? Oil Catch can. On our LSX motors the rocket scientist have developed a PCV through our valley tray. It is routed up to the intake throttle body. OK. Well a oil catch can separates oil mist from the air and then re-introduces a much cleaner air back into the throttle body. Looks like this.
From the bottom of the valley cover up to the top of the catch can...filtered through the wire mesh stuff.....clean air back into the throttle body...
http://img.photobucket.com/albums/v6...PCV3Medium.jpg
Yeah for us....well we are not finished yet. We need to plug the PCV...or some call it a PCV delete as we don't want to re-introduce the burnt gases back into our air/fuel mixture. OK plug the passenger side vent that was re-introducing these burnt gases back into the air/fuel....here it is capped off on my GTO...see it right there with the black cap....
http://img.photobucket.com/albums/v6...PCV7Medium.jpg
Brilliant! Wait a minute...I gotta vent all that crankcase pressure or my rings ain't gonna seal right and I'll be leaking oil everywhere......so lots of guys just vent via a cheap oil breather cap......like this one....
http://www.pfyc.com/pc/GN3020/GNUNDE...er+Filter.html
And you can see I have one on the passenger side valve cover....this is good for most LSX engines with some mods....as you go up the horsepower ladder this one vent cannot handle all the crank pressure....lot of you nitrous and forced induction folks can attest to blowing the dipstick out and spraying down your motor with oil can't you :) This is caused by too much crank pressure.... so many vent the other side as well.....and this is all good for I would say up to 600'ish RWHP. Now this pressure will come with some oil mist also. The passenger side oil cap breather I have does pool some oil down in the neck but has never came past the filter part. As for venting the other side (drivers side) for some additional venting capability GM was nice enough to provide us with a capped off ready made solution....it comes capped from the factory at the rear of the drivers side valve cover....here it is...now in this picture I already have my vent hose on it....but you will see a black rubber cap on yours...
http://img.photobucket.com/albums/v6...PCV5Medium.jpg
Some folks just put a little 3/8" KN type filter ( I get them at AutoZone for about $7 bucks) on there with a 3/8" hose splice and they are done. But I am a not enamored with wiping up oil mist off my engine and have installed an in-line oil/air separator I got from Home Depot for like $8 bucks. This allows the pressure to escape and I catch any oil before it vents into the engine bay. Here is the setup.
http://img.photobucket.com/albums/v6...PCV6Medium.jpg
http://img.photobucket.com/albums/v6...PCV4Medium.jpg
I just drilled two little 1/4" holes in the rain drain lip there and tie wrapped the setup....it ain't going anywhere and looks good.
So now you are catching the oil in your catch can. You are venting your crank pressure out. You have plugged your PCV. You can make more power...not be fouling plugs....not coating your intake and throttle body with oil....all good things.....
Once you pass 600+RWHP you will need to start looking at vacuum pumps....but this solution is clean/cheap/easy and makes it possible for your tuner to get aggressive without setting off knock sensors....your getting the crap out of your crankcase and oil so your engine runs cleaner....your relieving pressure so you instantly are reducing resistance to your pistons coming down (quicker revs gets you into your power band quicker) so you go faster. Quick=Fast.
I don't know if any of this helps anybody at all....but there is my humble take on the subject. Feel free to challenge/discuss/ask....I've been married so long I have no ego left.
http://img.photobucket.com/albums/v6...PCV2Medium.jpg
