Catch can routing and hose size

[robbbc]

I'm pretty much lost when it comes to the pcv system. Im not sure which is "dirty side" or "clean side". Is there a minimum size hose to run for my catch can? I currently have a 3/8 hose from passenger and driver side valve cover merging into a single 1/2 inch hose going into the can. From the can, I have a 3/8 line going to my intake. I have a 3/8 hose from the valley plate to the intake tube in between the maf sensor and throttle body. Does the routing sound ok or is there a better way to route it?

Engine is ls7 converted to wet sump with around 600hp. Mighty Mouse catch can with breather top. It used to spew oil out of the valve cover until I added the second line. It has since stopped spewing from the valve cover but I am getting more oil in the can than I would like. The motor is a new build with 4400 miles on it. Should I increase the size of the 3/8 hoses and if so, what are you guys using for fittings? Any info you guys could provide would be greatly appreciated.

Thanks!

[TANKMASTERJ]

I'm running your same LS7 convert to wet sump. Big cam, ported heads. I didn't get hardly any oil in catch can at 2000 miles. But maybe a couple of pop caps full with mixture of oil condensate water. Bjt I didn't want any of that sucked back down my intake so I run two cans, both nuke performance, one for valve covers, one for valley.
Works great. No smell under hood or in car. No slobber, very little oil in can. I don't think there will be enough to even drain any until 10k miles because at 2500 almost none. The valve cover can I have both Valve covers T into one -10 and into can. Can has a vent kindig like your mouse can but different. I also have the output of that can a hose to below the car. Again no slobber no fumes out of it. So it can breath out when your on the throttle, and it can breathe in when you let off and create vacuum. So in other words it pukes air when it needs to and breathes in when it needs to. Because the valve covers are really a separate unit as far as air flow from the intake system no tuning issues be are realized from any fresh air sucked in.
My other can is valley to can input and can return to intake suction. Both cans have a dipstick to check. Valve covers is all -10 fittings and hose. Valley can is all -6 fittings and hose.
No adverse effects on my tuning. I can jab throttle, dog it,get off whatever all is good. Remove intake tube and it's very clean.

[robbbc]

Tank- how would that need to be set up if it utilized only 1 catch can like in my scenario?

[TANKMASTERJ]

I'm definitely no expert but chase bays has a setup for an LS7 with one can. You can Google them and check the diagram.
I would think you just T the valve covers and valley into can. However you do need fresh air coming in to the valve cover. So if you T it you need fresh air from right behind your maf sensor feeding one valve cover. That way your not sucking in in metered air. At least that's my understanding.
In metered air isn't an issue on mine because valve covers are separate and don't affect intake air much.
I'm sure some other guys on here probably have better advice. But check out Chase Bays diagram

[streetk14]

You have your can setup backwards; at least compared with how the factory PCV is usually setup (and how I have mine). The “clean” side is the fresh air the system draws in. This is from the air intake tube after the MAF to the valve cover. The “dirty” side would be the line between the valley plate and intake manifold. This is how a factory wet sump LS3 is set up. You want your catch can inline on the dirty side; valley plate to catch can — catch can to intake manifold.

[robbbc]

Thank you! Since my original post, I have swapped hose routing and added a 5/8" hose as a test and am well pleased with the outcome so far. i will look at the routing tomorrow and hook it up as you say and see if it helps.

[robbbc]

Streetk14, thanks for the explanation. I just confirmed that I now have it set up as you said. 3 times i emailed and sent pictures to mighty mouse and 3 times i was told to hook it up as i had it. It was pulling so much oil into the can that i started to think there was a mechanical issue. I could only drive an hour and have 6-8oz in the can. I drove for 3 hours, spirited and casual and got maybe .5-1oz. i will be increasing the size of the system to either half inch or 5/8 hose in the near future and suspect that the amounts in the can will continue to decline.

[streetk14]

Thank you! Since my original post, I have swapped hose routing and added a 5/8" hose as a test and am well pleased with the outcome so far. i will look at the routing tomorrow and hook it up as you say and see if it helps.


The valley plate connection always goes to the intake manifold barb behind the throttle body on factory setups, so that’s definitely how you want it.

As far as the clean air side, I’ve just ran the stock configuration of one 3/8” hose from the intake tube to the passenger side valve cover barb on several builds. I ran it this way on a 730 whp supercharged LS3, and never had any crankcase venting issues. I don’t think you’ll see any benefit from the two hoses connecting both valve covers when everything else is connected like it should be. I guess it won’t hurt anything to do it that way though.

[robbbc]

Good to know. I could experiment with the hose size now that the routing is correct. Just the routing itself has made a dramatic difference and has eased my mind alot!

[robbbc]

Just wanting to close this out. I went with 8an hose size and different routing and reduced the amount of oil in the catch-can SUBSTANTIALLY!