Forced Induction Superchargers | Turbochargers | Intercoolers

Is this catch can setup safe to run like this?

Old May 30, 2026 | 05:46 PM
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Default Is this catch can setup safe to run like this?

Shop did my twin turbo kit on my LS3 and has what appears to be the crankcase port if I am correct on that one into the can into oil cap, and the manifold port capped, and the valve cover ports just vented to atmosphere....here are pics. I know everyone does this all kinds of different ways I just want to be sure this isnt gping to cause any issues down the line.



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Old May 30, 2026 | 07:33 PM
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Assuming that catch can is vented its just performing as a breather , you have no actual pcv system . I myself wouldn't run it that way , others will chime in I'm sure
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Old May 30, 2026 | 07:34 PM
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Originally Posted by GMCGreg
Assuming that catch can is vented its just performing as a breather , you have no actual pcv system . I myself wouldn't run it that way , others will chime in I'm sure
yes it is vented up top the can
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Old May 30, 2026 | 11:07 PM
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You should plug the open ports on the valve covers or run them into the catch can also. With them open dirt and debris can get inside
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Old May 31, 2026 | 06:21 AM
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Originally Posted by Lsxford
You should plug the open ports on the valve covers or run them into the catch can also. With them open dirt and debris can get inside
Ok, no more room in this can though, wpuld have to do another can, do they have be capped or can breather filters be ran on them? Also is this right with a turbo setup crankcase port into can and the manifold port capped?
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Old May 31, 2026 | 07:42 AM
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Are those ports actually left open? Not good.

The hose to the breather can will also act as a p-trap as it collects oil, and hold pressure in the crankcase. Think of the design of a manometer.
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Old May 31, 2026 | 07:52 AM
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Originally Posted by YukonJack
Are those ports actually left open? Not good.

The hose to the breather can will also act as a p-trap as it collects oil, and hold pressure in the crankcase. Think of the design of a manometer.
Yes those valve cover ports are just left open as shown. What should I do about those?
Also the crank case line is the only one into that can, can is vented though is that not relieving some crank case pressure with the can being vented up top?
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Old May 31, 2026 | 08:19 AM
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Cap the passenger valve cover and add a breather to the driver side port.
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Old May 31, 2026 | 08:23 AM
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Originally Posted by brutalzo6
Cap the passenger valve cover and add a breather to the driver side port.
Ok still new to the turbo and boost stuff for these engines, so bare with me, so why can the driver side be open/vented but passenger side capped?

Looks like the only things the shop capped as is is the manifold port next to the crankcase line which is into a vented can. And the passenger side to port is capped also
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Old May 31, 2026 | 11:48 PM
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Originally Posted by zinsavage123
Ok still new to the turbo and boost stuff for these engines, so bare with me, so why can the driver side be open/vented but passenger side capped?

Looks like the only things the shop capped as is is the manifold port next to the crankcase line which is into a vented can. And the passenger side to port is capped also
In your second pic it looks like there is another hose on the side of the catch can, possibly going to the other side or the the valley cover? I may be seeing something else. I like to vent both valve covers to the catch can through 10an or 5/8 hose.

The driver side port is the "PCV valve" port. On youre valve cover it appears actually to just be a metered orifice instead of a valve. Thats the side that is hooked to manifold vacuum in the stock configuration.

You can plug them both, put filters on both, or put a filter on just 1 but none of them should be open. If the catch can is vented in 2 places i would plug them both. If it only has the 1 line from the passenger side i would try to vent the driver side also. Preferably by routing it to the catch can but a little filter will work just fine. You want it to be able to vent all the crankcase pressure. If its not venting enough it will usually just blow the dipstick out, but theres a chance it could blow out a crank seal or a valve cover gasket. With them being open dirt, dust, bugs etc can and will make its way inside the crankcase

Edit- The hose coming off the passenger side goes down and then back up. So moisture may build up in the hose creating a blockage and not let it vent. Think about a p-trap under your sink or inside a toilet. In plumbing the p-trap prevents gases from the sewer to come up from the drains. That hose may have the same effect. It really shouldn't go down and then back up. It may be fine like it is just trying to clarify what was said above.


Last edited by Lsxford; May 31, 2026 at 11:57 PM.
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Old Yesterday | 03:20 AM
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Originally Posted by Lsxford
In your second pic it looks like there is another hose on the side of the catch can, possibly going to the other side or the the valley cover? I may be seeing something else. I like to vent both valve covers to the catch can through 10an or 5/8 hose.

The driver side port is the "PCV valve" port. On youre valve cover it appears actually to just be a metered orifice instead of a valve. Thats the side that is hooked to manifold vacuum in the stock configuration.

You can plug them both, put filters on both, or put a filter on just 1 but none of them should be open. If the catch can is vented in 2 places i would plug them both. If it only has the 1 line from the passenger side i would try to vent the driver side also. Preferably by routing it to the catch can but a little filter will work just fine. You want it to be able to vent all the crankcase pressure. If its not venting enough it will usually just blow the dipstick out, but theres a chance it could blow out a crank seal or a valve cover gasket. With them being open dirt, dust, bugs etc can and will make its way inside the crankcase

Edit- The hose coming off the passenger side goes down and then back up. So moisture may build up in the hose creating a blockage and not let it vent. Think about a p-trap under your sink or inside a toilet. In plumbing the p-trap prevents gases from the sewer to come up from the drains. That hose may have the same effect. It really shouldn't go down and then back up. It may be fine like it is just trying to clarify what was said above.
The only thing into that catch can is the crankcase port/line, which runs into the oil cap line, only things I see capped are the manifild port next to the crankcase port and other side manifold/tb port. The port on the valve cover of both sides are left open/exposed in the pics
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Old Yesterday | 08:14 AM
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Pic below shop told me that Left hand is OEM evap, right sides OEM fuel pipe, leave them open to vent, and something about right side doesnt matter really not plugged into anything. So guess all of that was eliminated with the fore fuel system...no clue.


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Old Yesterday | 08:46 AM
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Depends on which Mighty Mouse can that is, some preserve PCV function and some do not and both are plumbed differently. That one looks like it might be the PCV type, so I'd add a small length of hose with a small filter on the end to the driver side valve cover vent and run it over to the fender area so it's out of the way then cap the passenger side. Under normal driving the intake will pull air in through the driver valve cover vent, through the engine, through the can and into the intake hence the PCV function. Under WOT there's a valve inside the catch can that will close and all the pressure gets vented through the large AN line, through the can and out the top of the can.
Something like this is what I used before.



Regarding the Fore fuel system, it probably uses the factory feed line as the return to tank, so the factory return line is no longer used. I don't like open lines just sticking out there so I'd cap them all, the tank has its own vent so that shouldn't need to be open anyway.
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Old Yesterday | 09:53 AM
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Originally Posted by Black_Sunshine_99
Depends on which Mighty Mouse can that is, some preserve PCV function and some do not and both are plumbed differently. That one looks like it might be the PCV type, so I'd add a small length of hose with a small filter on the end to the driver side valve cover vent and run it over to the fender area so it's out of the way then cap the passenger side. Under normal driving the intake will pull air in through the driver valve cover vent, through the engine, through the can and into the intake hence the PCV function. Under WOT there's a valve inside the catch can that will close and all the pressure gets vented through the large AN line, through the can and out the top of the can.
Something like this is what I used before.



Regarding the Fore fuel system, it probably uses the factory feed line as the return to tank, so the factory return line is no longer used. I don't like open lines just sticking out there so I'd cap them all, the tank has its own vent so that shouldn't need to be open anyway.
Its the dual inlet race can from mighty mouse
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Old Yesterday | 10:28 AM
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Then it should be plumbed as such according to their website, no PCV function on this model. If the shop opted to use the valley cover vent instead of the driver valve cover, then I'd make sure MM approves of that change. I'd also ask the shop why they opted to not follow the manufacturers recommended installation instructions and if there were any other items in which they opted to not follow the manufacturers recommended install instructions. Next thing you know you're having issues elsewhere because the shop took the path of least resistance.
MM mentions a "Cyclone" effect utilized and the orientation of the ports to a specific side of the engine to achieve this effect. Also, the routing of the large AN hose which is current drooping down will fill up with fluid and cause a venting issue according to their website. That large AN line is the main vent under WOT and if its full of oil when that occurs then the pressure will have a much harder time getting out.
I would message MM and ask them if the current routing is okay and fix the large AN line routing.



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Old Yesterday | 10:51 AM
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Originally Posted by Black_Sunshine_99
Then it should be plumbed as such according to their website, no PCV function on this model. If the shop opted to use the valley cover vent instead of the driver valve cover, then I'd make sure MM approves of that change. I'd also ask the shop why they opted to not follow the manufacturers recommended installation instructions and if there were any other items in which they opted to not follow the manufacturers recommended install instructions. Next thing you know you're having issues elsewhere because the shop took the path of least resistance.
MM mentions a "Cyclone" effect utilized and the orientation of the ports to a specific side of the engine to achieve this effect. Also, the routing of the large AN hose which is current drooping down will fill up with fluid and cause a venting issue according to their website. That large AN line is the main vent under WOT and if its full of oil when that occurs then the pressure will have a much harder time getting out.
I would message MM and ask them if the current routing is okay and fix the large AN line routing.

Well this one on their website says its for crancase only, they have the crankcase port/vent line in there and to the oil cap, unless im missing something here it says this can is only for crankcase venting. Below is the one im using. Also I dont have any oil even in there that dripped out bottom empty cap whatsoever so far after 100 miles or so



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Old Yesterday | 11:06 AM
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Originally Posted by zinsavage123
Well this one on their website says its for crancase only, they have the crankcase port/vent line in there and to the oil cap, unless im missing something here it says this can is only for crankcase venting. Below is the one im using. Also I dont have any oil even in there that dripped out bottom empty cap whatsoever so far after 100 miles or so

That's right, so at idle you'll see condensation coming out of the can which the smell can get inside the cabin which is why some folks go for the PCV can. Feel free to run it and see how it does, you may hardly ever need to empty it so the hose routing might not be an issue. Just depends on how much boost you're pushing and how worn the engine is. I've been running my car at 15 psi and higher for years and have yet to empty my can. You'll know when it becomes a problem, it'll either push the dipstick out, push a seal out or start leaking oil in random places.
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Old Yesterday | 07:37 PM
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I'm not using forced induction but I'd still try to utilize this type of setup to ventilate the crankcase.
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