[smanders]

Updated: 9/26/2022 based on conversations below.

I'm looking to install a system on my car and started to realize there are a lot of different approaches to solving this problem that have come up over the years. I regularly HPDE my GT-R so that's the perspective I'm coming from. Recirculation options are more interesting for me due to the amount of time I'm under sustained boost.

I selected these four below as their approaches are all different. I'm sure some of these statements are inaccurate so I'm hoping others can help clarify. There are plenty of other options out there but most would overlap with one of these solutions or a subset of them. Thanks for any feedback.

The information below was gathered by myself looking through the installation manuals, GTR Factory Manuals, Forums threads, and deduced through my own logic.

• GT1R AOS ($750)
  • Pros
    • Closed System
    • Maintains Vacuum in Valve Cover
    • Cleaned air vented to the intake
    • Recirculation of separated oil via dipstick
  • Cons
    • Does not have the coolant interface to help reduce froth like in IAG's AOS system or Radium's AOS
  • Note: Seems to be the same principles of the AMS Catch Can ($613) - It is a matter of which one performs the Air/Oil Separation better
• BoostLogic Breather ($1248w/High Flow Fittings which is necessary)
  • Pros
    • Relieves more Crank Positive Pressure while on boost than other solutions due to the use of the filler neck
    • Removes more blowby while on boost
    • Recirculation option available via dipstick
      • Since the Valve Cover basically stays at atmosphere it should not be pulling oil in from the valve cover
      • With this design most if not all of the contents will be blowby which you do not want going back into the oil
  • Cons
    • Could have bad smells coming from engine bay
    • Valve Cover at atmospheric pressure? Bad or Good?
    • Vents significant amount of blowby to Atmosphere instead of Intake while on boost (good and bad)
    • In general I have read that if venting to the atmosphere that a 10AN fitting is best - BoostLogic's is 8AN to the filler neck
• Radium 3 Catch Can Setup ($610)
  • Pros
    • Closed System
    • Maintains Vacuum in Valve Cover
    • (2) Catch Cans for valve cover - one for each side for increased capacity
    • Cleaned air vented to the intake
    • (1) additional Catch Can captures PCV line when off boost
      • Partial Throttle, Idle, and Cruising
    • Stock PCV air return to intake manifold is maintained after going through the catch can
  • Cons
    • No recirculation option since it is a "Catch Can" system
    • Catch Cans could fill up quickly at Track Event
    • Does not relieve Crank Positive Pressure while on boost
• GotBoost Dual Catch Cans ($595)
  • Pros
    • Closed System
    • Maintains Vacuum in Valve Cover
    • Cleaned air vented to the intake
    • Relieve some Crank Positive Pressure while on boost since the inlet is always under a vacuum so essentially the PCV is always open
      • However I have heard that the vacuum at the inlet is minimal when at full boost but technically it is still a vacuum
  • Cons
    • No recirculation option
    • Catch Cans could fill up quickly at Track Event
    • Passenger Catch Can utilizes vacuum from one inlet to pull from both valve covers - vacuum in valve cover will not be as strong
    • Driver Catch Can utilizes vacuum to pull PCV air while not on boost
    • Intake Manifold is capped off - Good I guess but that Catch Can could fill up quickly?
    • There could be an imbalance of what is flowing into each inlet? Is that a problem or insignificant?

Summary: BoostLogic's filler neck tap is a great idea to relieve a bit more crank positive pressure while on boost. However it seems like the air it pulls should be sent through an AOS system and into the turbo inlets instead of vented to the atmosphere for Track applications. I also like GotBoost's solution utilizing one of the inlets to pull from both valves but is the amount of vacuum OK? Is the potential for imbalance on the turbo inlets with regards to fuel/oil a real issue? Is splicing into the PCV system really worth it like GotBoost and Radium do? If so, I think it would be better to let the manifold provide the vacuum instead of capping it off like in the GotBoost system. But the GotBoost solution does keep the PCV open while under boost, but would think the filler neck would relieve Crack Positive Pressure quicker...maybe?

 

[smanders]

The pressure differential evacuates the block under boost.

Hmm so I am trying to process that comment. I am under the impression that the PCV only opens when the pressure in the intake manifold is lower than the crankcase. When in the boost, the intake manifold pressure is much higher than the crankcase pressure, even when blowby is at its peak, so the PCV valve is closed. How else would the crank positive pressure be getting released? Its my understanding that in the GT-R the crankcase and value covers are separate spaces. Can someone comment on that?

 

[smanders]

This is an excellent write-up regarding Catch Cans in General from Radium.

Their diagram shows the crankcase and valve covers sharing connected spaces within the block. However I'm not sure the GT-R is set up that way. The PCV does not thread into each valve cover like a lot of inline cars. The PCV valve sits on top of the crankcase under the intake manifold and only feeds into the intake manifold.

Does anyone know if the crankcase and valve covers are connected and maintain the same pressure in the GT-R?

 

[smanders]

Thanks

They are all connected internally so whether you pull vacuum from the valve covers, oil filler cap, or pcv valve they will all evacuate the block. Off boost the intake manifold generates significant vacuum so it is a great source to evacuate the block and requires a stand alone catch can. Once on boost, the intake manifold PCV valve closes so the only ports on the engine still able to evacuate air are the valve covers. On boost the turbo inlets are generating a lower pressure (vacuum) vs the block pressure so this pressure differential pulls air out of the block.

They are most definitely connected via wide open internal passages. However - there are several internal baffles that serve to separate oil from the blowby gasses before it transits out via the PCV or valve cover outlets.

John-

Thanks for the info 240Z and JohnnyTSi. That is good to know. Yes, I will need to rethink and update my bullets in the first post.

Its interesting that Radium makes a generic AOS but does not create a kit utilizing it for the GT-R.

 

[smanders]

Just to wrap up my catch can project, I ended up going with the Radium Triple Catch Can solution. It seemed to retain the stock functionality and pressures while providing the most filtering. I also install the Radium petcock drain on the PCV catch can that goes in with brake booster. The petcock valve is near the bottom and zip-tided up just inside the under panel where it breaks from the front section.

I did need to reroute my vacuum line for my FI Exhaust. It still functioned but the Catch Can in the brake compartment was kinked a bit more than I wanted. So I re-routed that vacuum line through the same hole that was used for the catch can hoses.

 

[smanders]

What part(s) did you order for that?