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more crankcase ventilation

T

turbojose

Active member
Joined
Feb 22, 2009
Location
SF bay area
Ok... so I didn't want to hijack the current thread, but I'm try to decide on an improvement to my stock pcv system.... I am considering pulling from the valve cover as well as the original pcv box, but I don't quite understand the differences between the catch cans with filters on top, and the closed systems.... seems like you would need a closed system to in order to draw vacuum, but then I see all the fast guys using a vented system?? I'm just confused.... should I just shut up and run a vented system, or is there some advantages? I don't quite understand how a vented system even needs a vacuum line since it seems it would only be drawing from the filter??? right? and not from the crank case... I'm sure someone here has the answers... I've been lucky so far in getting the answers I needed here....

J
 
I installed a fitting and a tube from the fuel pump block off plate to my catch can injunction with the pvc system
 
Lots of people run vented systems for simplicity (or lack of understanding), but pulling a vacuum on the crankcase is ALWAYS a better option. More than anything els,e it helps promote good ring seal.


You have a few options really, depends on how 'oem-like' you want it to be. You can try to optimize the OE system, or you can run a hose from the valve cover to a catch-can, and then to a vacuum source. You've got a couple options there. You can run the catch-can line to the pre-turbo piping, but thats not recommended, as you may oil-soak your turbo and intercooler/piping. Another proven option is with an exhaust check-valve. It uses a venturi effect to draw a vacuum at all times, and that vacuum increases with increased airflow (basically, as power rises, exhaust gas volume roses, as does the amount of vacuum being created). Now, that doesn't always mean you'll have 100% vacuum at all times. Depending on how lose your motor is built, or how much ring blow-by you have, the vacuum method may simply be trying to overcome those positive pressures and you may end up with only a couple inches of mercury of vacuum. Still, it's better than none :)
 
kendogg said:
Lots of people run vented systems for simplicity (or lack of understanding), but pulling a vacuum on the crankcase is ALWAYS a better option. More than anything els,e it helps promote good ring seal.


You have a few options really, depends on how 'oem-like' you want it to be. You can try to optimize the OE system, or you can run a hose from the valve cover to a catch-can, and then to a vacuum source. You've got a couple options there. You can run the catch-can line to the pre-turbo piping, but thats not recommended, as you may oil-soak your turbo and intercooler/piping. Another proven option is with an exhaust check-valve. It uses a venturi effect to draw a vacuum at all times, and that vacuum increases with increased airflow (basically, as power rises, exhaust gas volume roses, as does the amount of vacuum being created). Now, that doesn't always mean you'll have 100% vacuum at all times. Depending on how lose your motor is built, or how much ring blow-by you have, the vacuum method may simply be trying to overcome those positive pressures and you may end up with only a couple inches of mercury of vacuum. Still, it's better than none :)
Click to expand...


Thank you for your reply.... Would you consider running an electric vaccum pump instead of pre turbo?
 
turbojose said:
Thank you for your reply.... Would you consider running an electric vaccum pump instead of pre turbo?
Click to expand...

I've seen it done before, but from what I've read, they tend to be problematic for most people.

I almost universally recommend this:
http://www.racersmarket.net/index.p...keyword=check&option=com_virtuemart&Itemid=93


The checkvalve included looks like this:
Crankcase_Evacua_4925e869ab633.jpg
 
turbojose said:
right on.... I may give that a try. I've always thought that was a racer type solution... is that ok for a daily driver?
Click to expand...


It's fine, so long as you plumb the checkvalve post-cat. If you plumb it pre-cat, you'll obviously oil contaminate your catalytic converter. Now, if you have tailpipe emissions testing where you are, you may been to disable this while doing emissions testing.
 
dbarton said:
I think that's misleading for a street car, unless you're running a straight pipe. Or can someone attest that you can get vacuum from an exhaust pipe with a muffler on the end?
Dave B
Click to expand...

All of the cars I know of that use this use a muffler. If your muffler is creating so much back-pressure that exhaust gasses are not flowing thu the exhaust, then there's a major problem.
 
kendogg said:
All of the cars I know of that use this use a muffler. If your muffler is creating so much back-pressure that exhaust gasses are not flowing thu the exhaust, then there's a major problem.
Click to expand...

Ok. I'm still a skeptic. Just that there isn't a muffler made that doesn't create back-pressure.

Furthermore... I recall several times many years ago that I blew the mufflers off the pipes in a Chevelle under load at 6k plus RPM, because I didn't have the clamps tight enough and not enough slits cut in the tube. That was some serious pressure.

I want to see someone put a vacuum gauge on the exhaust.
Dave
 
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dbarton said:
Ok. I'm still a skeptic. Just that there isn't a muffler made that doesn't create back-pressure.

Furthermore... I recall several times many years ago that I blew the mufflers off the pipes in a Chevelle under load at 6k plus RPM, because I didn't have the clamps tight enough and not enough slits cut in the tube. That was some serious pressure.

I want to see someone put a vacuum gauge on the exhaust.
Dave
Click to expand...

You missed the science behind the kit. It's not using 'vacuum' from the exhaust, we know there is positive pressure in the exhaust, although you do want to keep that at a minimum as well. It's using flow past the nipple (installed at a 45* angle) to create a venturi and create vacuum in the crankcase vent system.
 
kendogg said:
It's using flow past the nipple (installed at a 45* angle) to create a venturi and create vacuum in the crankcase vent system.
Click to expand...

Then I want to see someone put a vacuum gauge on the vent tube, with a muffler, under load, at high RPM.
Dave
 
Lots of hot rod guys find electric vacuums from other cars and use them to pull a good crank case vacuum. I think some early-mid 90s cougars got something like that. Also diesel cars might have them. Moroso sells them too but they're pricey.
 
thevolvokid said:
Lots of hot rod guys find electric vacuums from other cars and use them to pull a good crank case vacuum. I think some early-mid 90s cougars got something like that. Also diesel cars might have them. Moroso sells them too but they're pricey.
Click to expand...

Yep... found one in a mid 90's camaro at the PNP yesterday.... cant wait to give it a try.... Ill post pic later today.
 
Read that whole thread. The below pic was posted as their diagram. They claim 2.5 inches vacuum at idle and slightly more if you rev it.

crank_breather_jun09_0001.jpg
 
thevolvokid said:
Lots of hot rod guys find electric vacuums from other cars and use them to pull a good crank case vacuum. I think some early-mid 90s cougars got something like that. Also diesel cars might have them. Moroso sells them too but they're pricey.
Click to expand...


If you can find one, a secondary air injection pump from a BMW is the current choice over the GM pump (which I currently have, but am not using yet) They usually run the $60-$100 range.

http://forums.corvetteforum.com/1556192394-post17.html
 
I like the exhaust pipe approach, wouldn't have to package a gm pump under hood. Fwit, un unmolested gm smog pump (meaning charcoal still inside) I logged 2.5 inches vacuum in the case at wot. Same test with just preturbo suction showed no p?ressure or vacuum.
 
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