PVC Catch can system.... Final conclusive answer
03-28-2012, 12:42 AM
#261
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Hey guys...I have a few questions on the catch can setup for my rear mount...
Ive tried a recent set up I was running for a while on old motor, but now on the newer long block in (same just no bent valves in head etc LOL), I'm starting to have issues with vacuum lock...which I think is vacuum lock...and thats what im calling it...
I sent this to MM too, to see if he might chime in specifically...
My set up right now is on an LS4..327ci 5.3L Grand Prix GXP, E85, rear mount PTE unit, rear oil pump system....so let's break it down a bit...
SYSTEM:
1. I have my oil return to the oil filler cap
2. I have both valve cover ports going to a baffled catch can on AN bungs on one side of the can
3. I have a line running from the intake to the other side of the catch can routed post throttle body, and this line has a one way check valve in it to only allow vacuum through the can and close up for boost.
4. My catch can then has a check valve up top under a breather filter that allows the positive crank case pressure to vent to the top of the can. This check valve keeps me from pulling vacuum through the catch can while not in boost.
5. The can does collect the oily by-product and fills up just fine...both my check valves are working great.
SYMPTOMS:
Here recently since the newer motor in, I noticed that I was getting a vacuum sucking sound when I would pull the oil dipstick, and my oil pressure was running low. So, I pulled one of the valve cover lines to the catch can off and was pulling vacuum through the valve cover port and the dipstick!! LOTS OF VACUUM...and my car started to stumble probably due to the massive vacuum leaks! LOL My oil pressure was low on that note too...28-34psi...
TEMP. TROUBLE SHOOTING SOLUTION:
So, I just went ahead and ran the valve cover lines to atmosphere without the can and with no vacuum at all, and the car idled nicely, and Ive seen oil pressure Ive never seen before at idle...went from 35psi approx. up to 50psi! so that's good news...
THE QUESTIONS:
So, Im wondering what the best way would be to set up my can with a rear mount...obviously I think I'm getting vacuum locked in the crankcase and not allowing the pressure to release appropriately...I even get a vacuum suction and release sound after the motor is shut down and I pull the oil dipstick!!! that's how much vacuum I'm trapping with my system right now!
Someone told me that I need a "Clean air" vacuum/reference...and the only way to get that on a rear mount, well, is in the rear either on the top of the filter, or on the filter neck pre-turbo inlet, correct?
That's my system in a nut shell and the issue, and some notes on what temporarily relieved the vacuum pressure/lock if you will...
I am thinking that I can still run the set up the way it is, having the catch can having vacuum from the intake manifold and the valve cover ports going straight to the can and sharing that "dirty air" vacuum, and keep the check valve in the intake referenced vacuum line to keep boost out of the can....and then just run one more bung and line for "fresh air" and vacuum from the preturbo/inlet at the filter out back...will this work properly by pulling vacuum from the intake "dirty air" and the preturbo/inlet at filter "clean air" at the same exact time while in vacuum? I know the inlet out back will work great for a constant vacuum at WOT and boosting for sure!!
Thanks again! Pic below of what I'm thinking will work for me without using both ports on the catch can...this is routed similar to factory pcv system without the catch can basically...we dont have PCV valves either......I dont have the valley ports or any other of the ports the LS6 guys have in the cover etc...and I cant vent at the oil filler due to oil pump return, at least without modification...Im trying to do this without all that and work with what I have if at all possible...
And yes, the motor is sideways...I know..this is how I see it in my engine bay standing in front of the car...#7 is front right...its all *** backwards! LOL
Rossko
Ive tried a recent set up I was running for a while on old motor, but now on the newer long block in (same just no bent valves in head etc LOL), I'm starting to have issues with vacuum lock...which I think is vacuum lock...and thats what im calling it...
I sent this to MM too, to see if he might chime in specifically...
My set up right now is on an LS4..327ci 5.3L Grand Prix GXP, E85, rear mount PTE unit, rear oil pump system....so let's break it down a bit...
SYSTEM:
1. I have my oil return to the oil filler cap
2. I have both valve cover ports going to a baffled catch can on AN bungs on one side of the can
3. I have a line running from the intake to the other side of the catch can routed post throttle body, and this line has a one way check valve in it to only allow vacuum through the can and close up for boost.
4. My catch can then has a check valve up top under a breather filter that allows the positive crank case pressure to vent to the top of the can. This check valve keeps me from pulling vacuum through the catch can while not in boost.
5. The can does collect the oily by-product and fills up just fine...both my check valves are working great.
SYMPTOMS:
Here recently since the newer motor in, I noticed that I was getting a vacuum sucking sound when I would pull the oil dipstick, and my oil pressure was running low. So, I pulled one of the valve cover lines to the catch can off and was pulling vacuum through the valve cover port and the dipstick!! LOTS OF VACUUM...and my car started to stumble probably due to the massive vacuum leaks! LOL My oil pressure was low on that note too...28-34psi...
TEMP. TROUBLE SHOOTING SOLUTION:
So, I just went ahead and ran the valve cover lines to atmosphere without the can and with no vacuum at all, and the car idled nicely, and Ive seen oil pressure Ive never seen before at idle...went from 35psi approx. up to 50psi! so that's good news...
THE QUESTIONS:
So, Im wondering what the best way would be to set up my can with a rear mount...obviously I think I'm getting vacuum locked in the crankcase and not allowing the pressure to release appropriately...I even get a vacuum suction and release sound after the motor is shut down and I pull the oil dipstick!!! that's how much vacuum I'm trapping with my system right now!
Someone told me that I need a "Clean air" vacuum/reference...and the only way to get that on a rear mount, well, is in the rear either on the top of the filter, or on the filter neck pre-turbo inlet, correct?
That's my system in a nut shell and the issue, and some notes on what temporarily relieved the vacuum pressure/lock if you will...
I am thinking that I can still run the set up the way it is, having the catch can having vacuum from the intake manifold and the valve cover ports going straight to the can and sharing that "dirty air" vacuum, and keep the check valve in the intake referenced vacuum line to keep boost out of the can....and then just run one more bung and line for "fresh air" and vacuum from the preturbo/inlet at the filter out back...will this work properly by pulling vacuum from the intake "dirty air" and the preturbo/inlet at filter "clean air" at the same exact time while in vacuum? I know the inlet out back will work great for a constant vacuum at WOT and boosting for sure!!
Thanks again! Pic below of what I'm thinking will work for me without using both ports on the catch can...this is routed similar to factory pcv system without the catch can basically...we dont have PCV valves either......I dont have the valley ports or any other of the ports the LS6 guys have in the cover etc...and I cant vent at the oil filler due to oil pump return, at least without modification...Im trying to do this without all that and work with what I have if at all possible...
And yes, the motor is sideways...I know..this is how I see it in my engine bay standing in front of the car...#7 is front right...its all *** backwards! LOL
Rossko
Last edited by Rossko85; 03-28-2012 at 02:41 AM.
03-28-2012, 07:35 AM
#262
2 things you need to do
put pcv valve in line to intake.. the whole point of a pcv valve is to control airflow at vacuum which is your problem. a check valve does not do the same thing
second thing, ive set this up both ways, but in general you will need some fresh air inlet, it can be via hose to valley cover, to valve cover etc. prefer from a filtered location like pre-turbo but can just be a small filter anywhere (tho you dont get the added draft of the pre-turbo set up). for a motor making tons of blow-by you may get away without one.
only other comment i have is the pcv valve you are using to release pressure under your breather is quite the limiatation. just as they limit airflow into your engine, it will limit airflow out.
as far as the fix idea picture i would not run your boost sensitive equipment on the same circuit you are pulling valvecover oily-ness thru. i also dont like how that valvecover has a direct line to the intake vacuum. that means your catch can will not catch anything.
in the photo: lines from each valve cover (on a diagonal) to bottom of the catch can
top of catch can includes boostable pcv valve, goes straight to stock spot on intake
n/a application you see fresh air vent between throttle body and other end of valve cover, this could go to ls6 valley cover if you have one, or pre-turbo if you have one
all pcv air goes thru catch can, stock pcv operation, all positive pressure goes thru catch can as well before exiting the breather valve on top, open element style operation when making big power
put pcv valve in line to intake.. the whole point of a pcv valve is to control airflow at vacuum which is your problem. a check valve does not do the same thing
second thing, ive set this up both ways, but in general you will need some fresh air inlet, it can be via hose to valley cover, to valve cover etc. prefer from a filtered location like pre-turbo but can just be a small filter anywhere (tho you dont get the added draft of the pre-turbo set up). for a motor making tons of blow-by you may get away without one.
only other comment i have is the pcv valve you are using to release pressure under your breather is quite the limiatation. just as they limit airflow into your engine, it will limit airflow out.
as far as the fix idea picture i would not run your boost sensitive equipment on the same circuit you are pulling valvecover oily-ness thru. i also dont like how that valvecover has a direct line to the intake vacuum. that means your catch can will not catch anything.
in the photo: lines from each valve cover (on a diagonal) to bottom of the catch can
top of catch can includes boostable pcv valve, goes straight to stock spot on intake
n/a application you see fresh air vent between throttle body and other end of valve cover, this could go to ls6 valley cover if you have one, or pre-turbo if you have one
all pcv air goes thru catch can, stock pcv operation, all positive pressure goes thru catch can as well before exiting the breather valve on top, open element style operation when making big power
