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Running a daily driver, 6.0 with a precision 76/75 and will max out at around 12 lbs of boost. Curious about what size hose to run to the catch can. I have baffled valve covers and was curious if 6an fittings and hose is big enough or should I move up to 8an.
I'm running an LSA around 12 lbs with 3/8 hose as well. Goes to my Elite Engineering can. No issues and it catches a small amount of oil so I know it's working.
Go bigger than 3/8", I ran 3/8 on my LS1 w/ a 7875 at 12 lbs. and blew the dipstick out so 3/8 probably won't be enough and the way you'll find out is pushing a seal or dipstick coating the engine bay in oil.
I was using the MM PCV can and the fix was a -12 AN line to the driver valve cover and then plumbed with 3/8" line for the vacuum side.
If running a standard can, dual -10 AN lines would be sufficient, I'm of the mindset to go overkill on this topic because there is no downside in doing so.
It seems there is no "too big" setup when it comes to breather lines assuming they are baffled and not puking out oil. Two -10 lines were plenty on my WRX setup, one per valve cover.
I would think you could get by on 6AN lines in a PCV setup on a stock engine and 8AN lines would work better in a boosted application but most setups that I've seen, especially those for racing have all ran breather cans and the bigger the lines the better. My 427 has 10AN lines to a breather can but I'm considering going to dual breathers as I have no immediate plans to coat the intake manifold or the intake or exhaust runners and valves with lubrication from the effects of blow-by. Thanks but no thanks!
The Mighty Mouse PCV can works really well, it retains PCV function keeping the oil clean, has a check valve to keep boost out of the crank case, kept my intake squeaky clean and never left any oily residue in my engine bay.
Even pulling a valve cover the under side was always very clean.
A single can -12 or -14 AN would be ample for what you're goals currently are, I ran as high as 14-15 lbs. with the -12 AN and never had an issue.
Then use 3/8 braided (that's what I had laying around) for the vacuum side, hide the fresh air filter for the can inside the fender and you'll never have an issue at that level.
I run two -10 AN lines to my can now on my S484 car and have yet to have an issue.
Running a daily driver, 6.0 with a precision 76/75 and will max out at around 12 lbs of boost. Curious about what size hose to run to the catch can. I have baffled valve covers and was curious if 6an fittings and hose is big enough or should I move up to 8an.
I used -8AN with the largest can that Tracy Lewis sells. IMO get the largest can available and make sure it can be plumbed for boost. Make sure the can has enough ports and be very clear in your understanding of how each port works and its function.
Make sure you understand how to plumb the can so it can transition from vacuum to boost. If it isn't plumbed correctly you will blow boost into the can and into the crankcase as soon as you make boost. In order to stop that from happening you will need two high quality check valves. One for vacuum and one for boost.
If you don't already have one or both I would suggest that you get an LS3 driver side valve cover. The baffle design in the valve cover is much better than earlier versions because the baffles trap suspended oil in the valve cover so it doesn't make it's way into the catch can to be scrubbed. It is also suggested to install an ls6 valley cover if you don't already have one. The pcv valve is under the valley cover rather than external. It's port is under the TB. Pretty sure it is only -6an but not larger than -8an.
This diagram is a good example of how to plumb the system.
The purple line carries dirty air.vapors, and oil from the engine into the middle port on the can.
When the intake is in a vacuum state (NA) the blue line with the check valve is pulled open allowing cleaned scrubbed air from the can to enter the vacuum port on the intake just aft of the TB where it enters the intake.
As soon the intake transitions from a vacuum state to a positive pressure (boost) state the check valve in the blue line is forced to close due to boost (positive pressure in the intake). At the same time the check valve in the aqua colored line opens due to turbo vacuum and a venturi tube in the inlet. This line transfers cleaned scrubbed air from the can into the inlet to the turbo and up to the TB/intake.
Note: The dual check valves automatically default to the strongest evacuation source no matter whether the system is in a vacuum state or boost state.
The lime green line is routed from the turbo fresh filtered air inlet to a clean side separator on the passenger side valve cover. While the catch can eliminates most of the oil and condensates which come through the dirty side, the clean side separator, as the name implies, takes care of the little bit that can come through the clean side.
Anytime you exceed 2/3 throttle, reversion pulses reduce any measurable vacuum inside the intake manifold. When this happens, the PCV system stops evacuating and pressure builds in the crankcase. The oil vapors are pushed backwards out the fresh side inlet allowing ingestion. The Clean Side Separator intercepts these vapors
FWIW: The truck guys vent scrubbed vapors into the exhaust rather than recirculating it thru the turbo/procharger.
Last edited by dlandsvZ28; 08-10-2021 at 09:57 PM.
Reason: edit content
My Procharged LQ9 TSP engine only makes about 650 RHP at 10 to eleven PSI and I don't race so think I am safe. To go bigger I would have to tap a larger port into the intake when in the vacuum state and also retap larger holes for each port in the can.. According to Lewis the size of the can and the amount of vacuum when in boost makes a big difference too in order to pull from the can as much as what is going into the can.
The video below shows the crankcase pressure (NA) - not my car.
With the catch can system on my car, after two sessions on the dyno - about six hours total tuning, so far no popped dipstick and no fumes and gases exiting out of the clean side oil separator on the valve cover. Only had about a teaspoon of oil in the can. Intake is still dry as is the hat on the Procharger D1SC. I will continue to monitor.
This is the venturi tube the truck guys use when venting into the exhaust. It is -10 AN. It creates vacuum when in boost to pull scrubbed vapors from the can. It is huge. I modified it to fit the inlet hat on the D1SC.
Below is a read of the amount of crankcase pressure an NA small block makes.
"Here is a video to watch where Matt Scranton (we have raced together for decades) is demonstrating on a small cube NA V8 how much impact "venting" has on power loss vs pulling full time evacuation suction. Now keep in mind, a belt driven pump system will maintain far more vacuum at high RPM's than our street system can, and that makes it the best system for racing, but they wont last on the street as vanes, shafts, bearings and seals wear rapidly so we rebuild the race systems every half season to avoid failures (just as we replace lifters and valve springs mid season as well even if no signs of fatigue).
The first pull is simply "venting" the crankcase as most "professionals" do as they are only making assumptions in how to address these issues. The second one is with the belt on so it is pulling full time suction on the crankcase:"
This is a Z06 with only 13K miles. It's hard to imagine the amount of oil accumulated with only 13k. Oil contamination will cause detonation and timing retard and will also coke on the valves and in the plenum.
As pointed out in the video - a good source of vacuum is critical.
Hose size and setup is also highly combination dependent, some guys running looser ring gaps will build more pressure.
Over shoot it and then you don't have to find out the hard way.
My original 3/8" hose combo blew the dipstick out at 160mph at the top of 5th running down a nitrous vette (yeah I got him though ) and afterwards my buddy who was in the car filming couldn't believe the car didn't catch fire, oil was EVERYWHERE.
Then later on after replacing the clutch I noticed the new rear main seal I put in when I bought the car was leaking significantly, was it due to this or installation we'll never know.
I personally have a 6.0 and a 78/75 On3, I run Motion Raceworks baffled valve covers, and baffled dual -10 catch can. So I have a -10 from each valve cover, to the can. No intake source, nothing going into the intake. This is how I prefer it. I have never had an issue with oil residue in the engine bay, the baffles in the valve covers and catch can do their job.
There seems to be a some confusion between what is called a catch can and a breather can. Technically they're both catch cans but one is sealed and utilizes the PCV system while the other one ventilates to atmosphere and if you have a breather on your can then you are in fact ventilating to atmosphere.
For comparison,, on a 800 HP NA sprint engine,, -10 or -12 for all the breather hoses.. It takes that much to keep up with the scavenger system for the dry sump..
Lots of guys choke at the prices of the -12,, fight the blow by issues for a couple seasons then invest in the big tubes..
Bigger hoses also help get the evap gasses like water or methanol or ethanol out of your oil. So if your running and alcohol shots ,, its a good investment.. Makes the oil last way longer.
There seems to be a some confusion between what is called a catch can and a breather can. Technically they're both catch cans but one is sealed and utilizes the PCV system while the other one ventilates to atmosphere and if you have a breather on your can then you are in fact ventilating to atmosphere.
Not necessarily, the Mighty Mouse PCV can vents to atmosphere but also seals for vacuum operation.
Its not possible to vent a FI engine to anything other than atmosphere and maintain intake cleanliness.
ive got two mightmouse cans, one pcv with the checkball fitting and one open can. -10 on each stock valve cover. i tried to run it as pcv but it sucked more oil than i liked back into the intake. so both of them are just open to atmosphere at this point. still blows the dipstick up an inch every now and then.
ive got two mightmouse cans, one pcv with the checkball fitting and one open can. -10 on each stock valve cover. i tried to run it as pcv but it sucked more oil than i liked back into the intake. so both of them are just open to atmosphere at this point. still blows the dipstick up an inch every now and then.
Mine never sucked oil but it did fill up with that nasty, milky condensation.
Sounds like your 427 and big *** turbo are simply overwhelming the cans design which wouldn't surprise me at all.
Most guys at your level just have a couple -10 or -12 AN lines to a large breather can.
My current setup is a large can that probably holds half a gallon of fluid with dual -10 AN lines, one to each valve cover which is probably what you need with -12 AN lines instead.
Not necessarily, the Mighty Mouse PCV can vents to atmosphere but also seals for vacuum operation.
Its not possible to vent a FI engine to anything other than atmosphere and maintain intake cleanliness.
Most FI cars I've seen have all vented to atmosphere and besides do you really want the affects of blow-by mixing with the air/fuel mixture?
08-09-2021, 09:55 PM
Minimum hose size for catch can 
) and afterwards my buddy who was in the car filming couldn't believe the car didn't catch fire, oil was EVERYWHERE.
