PCV - Basic Question
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Drifting
Joined: Oct 2005
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From: Roanoke Virginia
PCV - Basic Question
Question is basic. Why ventilate? What's so great about burning nasty waste gasses up to keep the crankcase air clean, and gum up the upper end of the motor? Sheesh.
Also, to draw air through the (oil reservoir in my case) and eventually going into the intake manifold, you basically are creating a vacuum leak. Why not keep the vacuum high (and have better throttle response)?
All I see are disadvantages to PCV ventillation, when I put some thought into how the overall system operates and not take it for granted.
So I did reroute my PCV lines, and get faster throttle response (just great!), and it seems to run much better. So, then I really started thinking
Also, to draw air through the (oil reservoir in my case) and eventually going into the intake manifold, you basically are creating a vacuum leak. Why not keep the vacuum high (and have better throttle response)?
All I see are disadvantages to PCV ventillation, when I put some thought into how the overall system operates and not take it for granted.
So I did reroute my PCV lines, and get faster throttle response (just great!), and it seems to run much better. So, then I really started thinking
Safety Car
Joined: Dec 2004
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From: stafford country, va. Avatar: Me on turn 3 @ Bristol (The World's Fastest Half-Mile)
Originally Posted by kelp
Question is basic. Why ventilate?
pcv or 'crankcase' ventilation relieves the buildup of pressure inside the crankcase/engine.
if the system is not ventilated you will build enough pressure inside the engine that 'seals' will begin to blow, the engine will need to work against the pressure, oil won't move as freely, etc., etc.
you don't have to route it into the intake if you don't want too, that's where the epa comes into the picture. instead of venting the 'gasses' into the atmosphier they (epa) mandate that the 'gasses' are returned to the 'system' and burned.
it is common practice to use a 'crankcase filter' on the vent instead of routing it back into the intake.
when it routes into the intake you are no longer getting 'clean air', you are getting a combination of air types. some hot, some not, some dirty, some clean.
Melting Slicks
Joined: Sep 2004
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From: Long Island NY
I'd think that, especially for a street engine, the PCV system is a very good thing. It positively removes blow-by gasses, etc (fuel, vapor, etc) from the crankcase so that such contaminants do not condense into the oil. With just a mere breather and no PCV system, I'd think the inside of the crankcase and the motor oil would get dirty / contaminated much faster. The PCV is purging the crankcase all the time, pulling bad stuff out and sucking "clean" air in. The downside is that you can see oil contamination in the intake, heads, etc. Some people use an oil catch can to reduce this problem... basically a filter in the PCV path that separates the oil from the gasses so that not much oil vapor makes its way to the intake. Most motorcycles have such oil separators from the factory... and they work. I believe Elite Engineering makes an oil catch can for Corvettes. Personally, I'd much rather install a catch can and leave the PCV in place as opposed to undoing the PCV and adding a mere open breather... because I'd like to keep my crankcase clean. 
Melting Slicks
Joined: Sep 2004
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From: Long Island NY
EDIT: Sorry... accidental duplicate post... the forum has been running slow and quirkly lately... often the page times-out before the post goes in, I often lose my text before the post is submitted... very frustrating... I now "copy" my posts before hitting submit so I don't lose my text. Anyway, sorry for the extra accidental entry here... the post had timed-out and page went blank... I assumed the post was lost so I tried again... but alas the original HAD gone through also... ooops. 
Last edited by Vet; Sep 29, 2006 at 10:44 AM.
Race Director
Joined: Mar 2005
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From: Austin Texas
Any internal combustion 4 cycle motor builds pressure in the crankcase, the pressure has to be relieved for the engine to operate correctly. Some extreme horsepower applications even use a pump to create a vacuum in the crankcase. The choice of where to relieve the pressure is yours. There are any number of ways to separate the oil from the blowby gases, aftermarket kits and DIY. Before pollution regulation we just vented the crankcase to the outside air. Now we vent the pressure to the intake to recover the blowby gases. You can just vent the crankcase but you won't pass a strict emissions test.
Safety Car
Joined: Dec 2004
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From: stafford country, va. Avatar: Me on turn 3 @ Bristol (The World's Fastest Half-Mile)
Originally Posted by Vet
I'd think that, especially for a street engine, the PCV system is a very good thing. .... With just a mere breather and no PCV system, ...the crankcase and the motor oil
Originally Posted by Vet
... get dirty / contaminated much faster .... The PCV is purging the crankcase all the time, pulling bad stuff out and sucking "clean" air in.
best of both worlds ??
what if both sides were pcv filter vented ?
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Drifting
Joined: Jul 2003
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From: Annandale VA
Originally Posted by Zig
will
hhhmm.. install an inline filter... (kinda like a motorcycle fuel line filter)... just keep an eye on it, don't want it to fill up ??
best of both worlds ??
what if both sides were pcv filter vented ?
hhhmm.. install an inline filter... (kinda like a motorcycle fuel line filter)... just keep an eye on it, don't want it to fill up ??
best of both worlds ??
what if both sides were pcv filter vented ?
There is no need for a pcv valve on the supply side. The whole purpose of the PCV valve is to let gasses go through, but no oil. Since there is no oil or crankcase fumes on the supply side, no need for a PCV valve.
Melting Slicks
Joined: Sep 2004
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From: Long Island NY
Originally Posted by Zig
...just keep an eye on it, don't want it to fill up ??
Drifting
Joined: Jul 2003
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From: Annandale VA
The LS2's are much better in this regard than the LS1's were, especially the earlier models before the LS6 intake manifold came it. The LS6 had the vent line coming from the valley cover instead of the valve cover, and worked much better.
Before the catch cans became popular, guys used to to the "vertical PCV" mod, where they used a PCV valve from an earlier year V-8, and mounted it vertically, which made it harder for oil to get sucked into the intake.
There is a fairly easy way to determine how much oil is getting past your PCV valve, and into the engine. Just remove your MAF and airbridge, reach into the throttle body and open the butterfly, feel the back of the blade. If your hand comes out all black with oil, you're getting contamination.
Before the catch cans became popular, guys used to to the "vertical PCV" mod, where they used a PCV valve from an earlier year V-8, and mounted it vertically, which made it harder for oil to get sucked into the intake.
There is a fairly easy way to determine how much oil is getting past your PCV valve, and into the engine. Just remove your MAF and airbridge, reach into the throttle body and open the butterfly, feel the back of the blade. If your hand comes out all black with oil, you're getting contamination.
Safety Car
Joined: Dec 2004
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From: stafford country, va. Avatar: Me on turn 3 @ Bristol (The World's Fastest Half-Mile)
Originally Posted by Vet
On a few motorcycles I had, there was an "oil separator" tank inline between the crankcase and intake. It had a drain tube at the bottom, and every so many miles you were supposed to pull the plug from the drain tube and drain out whatever was in there.
i'm currently enviromentaly bad. i was going to have the crankcase vent on my bike into a flask, mounted up against the oil tank. but currently, it just vents to the outside.
popping a drain valve into the bottom isn't a bad idea.
Originally Posted by Vet
I did so, and indeed, every few thousand miles some crud would come out... seemed to be a combination of oil and water, a mayonnaisey kinda solution.
Originally Posted by Vet
I once worked on a 455 engine (7.5 liter) with no windage tray and a PCV valve that was in a direct line of fire to the crankshaft with no baffle...
Originally Posted by Vet
that thing was sucking oil into the intake by the quart, that was a big problem that needed to be dealt with.
Originally Posted by Vet
I'd like to think that a stock LS2 that does not see constant track use can get away without any PCV modification. Comments?
how much of a difference would it make ? under what type of conditions ? etc.
Last edited by Zig; Sep 29, 2006 at 01:21 PM.
Safety Car
Joined: Dec 2004
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From: stafford country, va. Avatar: Me on turn 3 @ Bristol (The World's Fastest Half-Mile)
Originally Posted by HITMAN99
...
Before the catch cans became popular, guys used to to the "vertical PCV" mod, where they used a PCV valve from an earlier year V-8, and mounted it vertically, which made it harder for oil to get sucked into the intake.
Before the catch cans became popular, guys used to to the "vertical PCV" mod, where they used a PCV valve from an earlier year V-8, and mounted it vertically, which made it harder for oil to get sucked into the intake.
all of the old v8 pcv valves i've worked with have been vertically plugged into the valve cover.
Originally Posted by hitman99
The LS6 had the vent line coming from the valley cover instead of the valve cover, and worked much better.
Drifting
Joined: Jul 2003
Posts: 1,796
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From: Annandale VA
It wasn't quite that simple, as the LS1 PCV mounting assembly also served as a ground strap (don't ask why, I don't know). There were dozens of earlier PCV valves that would work.
Why in the world would you want to retrofit the earlier LS6 intake and valley cover to an LS2?
There were lots of guys who wanted to swap the early LS1 intake for the LS6, for flow reasons. You had to grind off a casting boss inside the engine to do it, otherwise it was a direct bolt-on. The valley cover feed to the PCV was just a convenient add-on benefit.
Why in the world would you want to retrofit the earlier LS6 intake and valley cover to an LS2?
There were lots of guys who wanted to swap the early LS1 intake for the LS6, for flow reasons. You had to grind off a casting boss inside the engine to do it, otherwise it was a direct bolt-on. The valley cover feed to the PCV was just a convenient add-on benefit.
Melting Slicks
Joined: Sep 2004
Posts: 3,488
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From: Long Island NY
Originally Posted by Zig
pcv valve that was in a direct line of fire to the crankshaft... ?? huh ? where was it located ? in the block ??
This has always been a problem with big old V8s... I've seen Buicks and other V8s that had their intake runners coated with oily sludge due to oil being sucked in though the PCV valve... intake valves fully coated with thick oil sludge, etc... ultimately resulting in detonation etc. I'll never understand why the manufacturers never seemed to try to do much about this problem, at least back then. All of those engines should have had some type of catch cans and/or improved PCV designs to keep oil out of the intakes.
Safety Car
Joined: Dec 2004
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From: stafford country, va. Avatar: Me on turn 3 @ Bristol (The World's Fastest Half-Mile)
Originally Posted by HITMAN99
Why in the world would you want to retrofit the earlier LS6 intake and valley cover to an LS2?
Originally Posted by HITMAN99
The LS2's are much better in this regard than the LS1's were, especially the earlier models before the LS6 intake manifold came it. The LS6 had the vent line coming from the valley cover instead of the valve cover, and worked much better.
i wasn't referring to the 'intake', just the 'vent'.
Team Owner
Joined: Oct 2004
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From: San Clemente CA
Originally Posted by Vet
EDIT: Sorry... accidental duplicate post... the forum has been running slow and quirkly lately... often the page times-out before the post goes in, I often lose my text before the post is submitted... very frustrating... I now "copy" my posts before hitting submit so I don't lose my text. Anyway, sorry for the extra accidental entry here... the post had timed-out and page went blank... I assumed the post was lost so I tried again... but alas the original HAD gone through also... ooops.
I thought it was just me.
