Catch can confusion

[Dblock]

Hi Guy,

 

When Im next free Im going to open up my plenum and clean the inside as my car is racking the miles now. So once I've cleaned that and the throttle body I'l want to install a catch can. Now most guides show two ports on the side of the engine but my car has a little pipe the plugs into the inlet pipe and Im pretty sure thats where the oil is coming from. So once a catch can is installed does the little pipe in the intake do nothing or do I have to connect that pipe somehow to the catch can?

 

Thanks

 

[GT4 Zed]

You can install your OCC on either the breather vent(small tube on driver side engune bank going into the plenum) or on the PCV side coming from the passenger side bank into the underside of the zed/intake tube.

As you have pointed out most oil vapours comes from the breather side while the PCV blowby is predominantly fuel fumes and very small amount oil vapours.

 

You should connect the pipe from the vent(breather or PCV) into the OCC inlet and another from the OCC outlet to the intake or plenum. So in essence you OCC "catches" the oil vapour and lets cleaner fuel vapour to go into the intake.

You can cap the intake or plenum ports and vent to air via a filter but for a non-race car this is extreme and could mess up your engine smooth running as it confuse the already metered air read through the MAF.

The single most important thing is to buy a baffled oil catch can which effectly traps and condenses the oil vapour and let the fuel vapour through and it's thus oil you have to drain from time to time. The common hollow OCC which is a majority even branded are hollow a do precious F all!! The vent vapours just go through it with very little catch!

 

I have been looking for a baffled OCC myself for sometime and the ARC would have been perfect but too expensive and rare. Get custom stuff made in the UK is also too rich but I have found a company in the states who do this and are renowned worldwide. I am putting an order for Wasso and me once I get the measurements of the various tube diameters.

Pm if interested for details.

[GT4 Zed]

The other question some may ask is why do you need an OCC?

Simple reason is to maintain a high quality intake air for optimum combustion and power.

The recirculated vapours from the vents effectively reduces your A/F mixture from burning well so the ECU retards timing giving you less power. Almost like running 95 RONinstead of 99.

The other reason is keeping the intake path, butterfly valves, intake valves clean as these become gunked up with oil or tarry stuff from burning oil and affects performance of these.

Finally you may say why does Nissan not do it OEM. Comes down to cost, emissions and the end user!

Cost is obvious as its one more item to add on the production cost.

Emission; it's easier just to route the vented air in the intake so it's burnt and "cleaned than adding OCCs or other complex cleaning or catching systems just for the sake of a very small loss in performance!

End user; how many of us will like to maintain an OCC. ie checking/draining it considering it will have no regular filling pattern unlike a service schedule!

It's for these reasons alot of stuff on modern cars are compromised to fit rules/regs, different climates, fuels and the variety of the end user expectations.

[evilscorp]

Nice post GT4 Zed, never knew that most catch cans were hollow. Might invest in one after your wise words

[Wasso]

I have the Cusco catch and it's just an empty can basically.

 

Baffled FTW!

[Dblock]

I'm wanting the catch can to keep my intake cleaner and oil vapours reduce Ron rating as you have said.

 

I thought all of them where baffeled! I was actually thinking of making one from air compressor parts . Just like a water trap as such.

 

So do I need two catch cans?

 

Could you show me where they go on a picture also?

 

Your advice is very much appreciated.

[Michael robinson]

Could you adapt the occ to drain the catched oil back into the system some how so you wouldn't have to keep draining it or is this a no no due to contaminates ???

[GT4 Zed]

I'm wanting the catch can to keep my intake cleaner and oil vapours reduce Ron rating as you have said.

 

I thought all of them where baffeled! I was actually thinking of making one from air compressor parts . Just like a water trap as such.

You can put some wire wool in a cheap OCC to provide a substrate on which the oil vapour will condense if you want to save money But it means you have to find one that you can open to put the wool in. You have to make sure the intake is below the wool and the outlet pick up is above the wool so it sucks out only the fuel vapours. I have seen a few OCC on ebay that can be adapted to do this. eg http://www.ebay.co.uk/itm/Black-Alloy-O ... 53ec0d29d2

The only isues is that it will not catch 100% but will be way better than the hollow OCC.

 

So do I need two catch cans?

Not necessarily. The most important one to have is on the breather side as most of the oil vapour comes from this The PCV side is not too bad unless if your rings are good and you have excessive blowby I will go for a custom dual can as there is not alot of room

 

Could you show me where they go on a picture also?

I'll take some pic tomoz but if you seach here Ian had a guide to sho where they go

 

Your advice is very much appreciated.

 

 

Could you adapt the occ to drain the catched oil back into the system some how so you wouldn't have to keep draining it or is this a no no due to contaminates ???

It can be done so far as you draind back into a low pressure area but i think it will be a major engineering exersice and you will be better off just emptying the can every now nd then. Its not like you have aliter coming out of it. more like 5mls per 1000 miles

[Tricky-Ricky]

Seems to me there is a little confusion over how the PCV system works, both the drivers side that comes from the cam cover to the plenum, and the passenger side that also comes from the cam cover to the intake are both part of the PCV system, but they work in different ways.

 

The drivers side is whats known as the idle/low throttle breather, in that this is the one that will cause the unwanted oil reside in the plenum and to a degree in the throttle body, as the VQ draws a lot of oil vapor from the cam cover/engine due to the high vacuum at idle/low throttle, this has a non return valve in between.

 

The passenger side is what is known as the full throttle breather, and works by the vacuum generated by the intake airflow across the tube fitted at right angles to the intake, this one does not require a non return valve, and also generates less vacuum than the other.

 

If you fit a catch tank, the best and most efficient option is to just fit it between the drivers side cam cover and the plenum leaving the non return valve in place, the length of the pipework and the tank should be enough to cause all the oil vapor to drop out before returning to the plenum, but as mentioned you can if it doesn't do the job due to say a worn engine etc, fill the can with stainless scourer's, but its important that the tank i 100% sealed or you will have idle problems.

 

Linking the drivers side and the passenger side to the same catch can can cause idle problems too, unless the passenger side is jetted to reduce the amount of air thats drawn in.

 

I have run a breather on just the drivers side for nearly tow years now and both my throttle body and plenum are spotless.

 

PS Just a note on the effects of oil vapor affecting AFRs, it will actually have no effect on the actual AFRs and in any case the ECU will compensate if the lambda feedback will deal with fueling trim if needed, unless there is a considerable amount of oil going in, and it goes beyond its limits.

Yes it true that a lot of oil vapor can lower the combusted fuel octane, which can lead to detonation, but this although can happen in extreme cases, is not a problem with N/A engines (with the exception of race engines)

It can however be a problem with FI engines, as the combination of critical fueling and timing needed to ensure detonation doesn't take place with pressurised induction can be effected by amounts of oil vapor decreasing the knock rating of the fuel.

[Dblock]

so leave the one that connects to the intake and just catch can the plenum ones?

[Tricky-Ricky]

so leave the one that connects to the intake and just catch can the plenum ones?

 

If your engine is healthy, thats all you really need, but like i said make sure you get one that seals, or can be made to seal OK, mine is just an ebay copy, i just added a silicone seal to the top and bottom joints.

[Dblock]

so leave the one that connects to the intake and just catch can the plenum ones?

 

If your engine is healthy, thats all you really need, but like i said make sure you get one that seals, or can be made to seal OK, mine is just an ebay copy, i just added a silicone seal to the top and bottom joints.

 

My car seems to run ok, anyway I could tell its not super healthy?

 

I take it the little connectors with jubilee clips wont make a great seal?

 

Silicone sealent? like the stuff you use in your kitchen?

[Tricky-Ricky]

so leave the one that connects to the intake and just catch can the plenum ones?

 

If your engine is healthy, thats all you really need, but like i said make sure you get one that seals, or can be made to seal OK, mine is just an ebay copy, i just added a silicone seal to the top and bottom joints.

 

My car seems to run ok, anyway I could tell its not super healthy?

 

I take it the little connectors with jubilee clips wont make a great seal?

 

Silicone sealent? like the stuff you use in your kitchen?

 

 

The right sized jubilee clips will be fine for pipework, and yes you can use kitchen type silicone sealant for the can but it does break down eventually as its not designed to be used with oil, there are silicones that are intended for motors though.

[Dblock]

thanks

[GT4 Zed]

Thanks for more input to this threads TR but you may have overread into bits of my explanations which is for sake of simplicity describing the PCV system as two entities one on each side.

Secondly Oil vapour does reduces the ignitability of the A/F mixture in the combustion chamber and hence would act like decreasing the RON value just like adding meth will increase it. This has nothing to do with AFR and I did not suggest that either.

I do agree that FI cars are more susceptible but you loose a very small amout of ponies venting blowby to the intake as per OEM setup which is standard on both FI and NA engines.

 

Dblock here with a schematic on how you can naffed a cheap eBay can or what a good can should be designed as.

 

I will be getting my dual can from him and for clarity It just two can adjacent to each other with no communication.

[Dblock]

So after much searching I'm going to follow this guide here

 

I couldnt find a decent baffled catch can for a decent amount of money.

 

This is taken from another forum but most do this

 

 

Also whats the point of the breather sometimes attached to the top of the OCC?