Catch Can Info and Plumbing

[curtisgoodman]

Hey everyone I just picked up mishimoto's new catch can design and I have some questions regarding plumbing... I've seen many many installation pictures and mounting options, searched and read some info regarding the subject but a couple questions I have are:

I see most people run 2 separate lines to the catch can is this necessary or can you Tee off the "C" hose that connects both valve covers and run a single line to the catch can?

Does the drivers side valve cover hose lead to a PCV valve? and if so is it okay to block that off?



My catch can only has one intake port and one exit port so I'm trying to make 1 hose from the valve cover breathers to the can... is this possible and how would you do it?

I'll also be running the vapour from the catch can to the turbo side stock location to burn it so i dont have to smell it.

Any thoughts or ideas?

Thanks,

Curt

[Skym]

Into intake (vacuum source) for road use due to emissions laws.

On racecars they have one hose from each camcover to catch can and usually vents to atmosphere via a vacuum hose from catchcan that's vented just behind engine (air running under car becomes the vacuum source). Also they block off the camcover to intake side ribbed nipple, hole on intake just after MAF piping and remove PCV valve, block the hole where PCV was located on intake manifold with a screw in bung (provided with some catchcan kits).

On some catch cans they have a filter on top, so one hose to catchcan from each cam cover, block off the camcover to intake side ribbed nipple, hole on intake just after MAF piping and remove PCV valve, block the hole where the PCV was located on intake manifold with a bung. But the filter can become blocked and causes breathing problems with the engine and there's no vacuum source, thus catchcan can fill after a couple of laps.

From what I understand, the PCV on intake is used at idle to help stop too much blowby entering intake and making the burn too dirty, thus causing idle problems. The PCV closes when intake is under boost and all the blowby goes out the exhaust side camcover vent hose to intake piping just behind MAF.

[curtisgoodman]

alright so blocking off the intake manifold side is ok thats good to hear (I've just capped it off)... since i only have 1 port on my catch can to plump into from the valve covers I'm either going to Tee off the hose connecting both sides and run 1 line to the can or I'll run 2 line one from each valve cover then Y them into the single port. On the turbo side I'll be using the stock hole just after the MAF to push the fumes back through the engine... I have a catch can that has a 40 micron filter on the top so i believe I wont be polluting my fuel to badly or at least less then i have been since i havent had a catch can yet...

Link to catch can

http://www.mishimoto.com/mishimoto-baffled-oil-catch-can.html

Thanks for the reply Skym, it seems very few are on here anymore to help which is a bummer i remember many many people back in 2008-2010 on here trying to help members...

[Skym]

That catchcan is designed to be on the exhaust side only (inbetween exhaust camcover breather / vent and intake piping to just behind MAF), hence one in and one out ports on the catchcan. Keep the stock PCV setup off the intake camcover.

Also size of catchcan is important, as it needs to be at least 2 litres for over 2000 cc capacity engine (look at local motorsport rules). For road use, can get away with 1 litre, but at least 2 litres is recommended.

With turbocharged engines you note the capacity of the engine and x 1.7 to get the real capacity of the engine.

[curtisgoodman]

wow 2 liters eh... I dont think the one i have is even close to that amount... sigh... and after all that reading i still didnt know what you just posted... ask questions first and purchase parts second lol...

Alright so now if i understand correctly I will retain the stock intake side to pcv connection and on the exhaust side i will run it to the catch can and from the catch can to the intake piping behind the maf... now do i keep the valve cover vents connected together with the middle hose or block them off and keep them separate? Also since u said i need to have 2L minimum will my catch can not work at all or will i just need to empty it more often... i have a drain kit coming for it so i could just setup a sealed container below my catch can to allow for more volume.

[Skym]

What you have would work ok for street use, around stock boost levels. On racetrack it fills up quickly, then oil enters intake, hence have to pit after a few laps to empty the catch can. Some people use a drain back to sump catch can setup on racetrack, so don't have to drain the catch can.

If want a factory solution, Nismo sell a drain back to sump version (smaller version of what they run on the Group-A engines).

Stock PCV setup goes like this on GTS RB engine (a PCV setup that's visable and easy to understand, but GTR engine is the same, except mounted at rear of engine and I think longer piping involved).

Intake manifold > PCV > vacuum hose > intake cam cover breather > vacuum hose inbetween cam covers > exhaust cam cover breather > vacuum hose > hardpiping > rubber intake pipe just behind MAF.

You fit that catch can inbetween exhaust camcover breather and hard piping with the supplied vacuum hose. The oil travels that way under boost (if higher than stock boost level).

[curtisgoodman]

thanks for the help again Skym, I'll plan a route back into the sump or I'll find a larger container for the catch can to empty into... I can't see how I would be going through that much oil if i've never had a catch can before and my oil level doesn't change between oil changes... in bc i was running 28psi, I'm running a little less here in Ontario cause of the lower octane fuel but i dont have a pool of oil in my intercooler but i can tell there has been oil thats travelled through the pipes because they all had a film on the inside...

[curtisgoodman]

anyways awesome info and i know what i must try and do now... thank you very much

[Skym]

You're welcome. What I mean by stock boost levels is someone on here had their GTR on the racetrack and dropping back to stock boost level reduced the amount of oil exiting the engine. It's constant high rpm, high boost levels on racetrack or even motorway in a lower gear, not a rev every once and a while like with street use.

The high pressure / blowby in the sump builds up and stops oil draining back to sump through the internal oil drains, so relieving the sump pressure via a hose to catchcan and then into intake bypasses the too small internal oil galleries in the engine. From what I understand, this is done via the multi stage dry sump pump, bottle with vent on it, hence why dry sump is best if running very high boost levels on RB engines for drag or track use.

Some use what they think is a head drain at back of head, but what that does is moves the blowby / pressure from sump to head (equalises the pressure in sump, head) to allow the oil to drain back to sump from the head through the internal oil drains.

At idle is where the blowby / pressure is higher, hence the need for a stronger vacuum source (direct to intake manifold), PCV to regulate the amount of blowby. That's why the intake side is not modified for street use. Too much pressure and it blows the turbo oil seal (has happened to some Skyline owners), etc. With racecars they are constantly moving, and at higher rpm, so the PCV is not needed and is just another thing to fail on the racetrack.

[curtisgoodman]

Alright lots of good info here, I do have a twin head drain back modification so that's a plus... I'll be taking your advice on hooking up my oil catch can for sure... I'll post some pictures

twin drain back mod... done this way because its lower than the frost plug to be more efficient...

[Skym]

With oil restrictors inserted into the oil galleries, the oil galleries become smaller, so the pressure / blowby builds up (I believe worse than factory). That's why bypassing to catchcan helps to relieve this pressure / blowby in the sump.

Some have found that running more than one hose to catchcan allows more pressure to be moved from the sump and it's not a good idea to put it into head, as still has to make it's way out the camcover breathers and into the intake.

The downside of putting blowby / pressure into intake is it spoils the burn in the cylinders (less oxygen) so results in less hp. That's why extractors help on higher hp engines, as they draw the dirty gas out of the cylinders which results in the engine running leaner (more oxygen is allowed into the cylinders vs same amount of fuel) and results in more hp (leaner A/F ratio) at a lower boost level.

That's why on racecars they run the catchcan to atmosphere, just behind engine via vacuum hose, as they need every last bit of hp and the air running under car is the vacuum source. But for street use it wouldn't pass emissions testing and lower road speeds, hence why car manufacturers put it back into intake.