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Old 19-01-2011, 09:22 PM   #1
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Catch Tanks, & PCV Systems.

I felt the need to write this up due to people thinking that there is only the one way to plumb in and use a catch tank, first it may help some to have a read of this,
http://www.autoshop101.com/forms/h63.pdf
which will explain the basics to those that don't already know.

Now the whole reason that a lot of people fit a catch tank is to try and eliminate some of the oil that gets drawn
into the intake system and not only lowers the octane rating of the fuel, (which is undesirable on turbocharged
engines) but also gum up throttle bodies, IC pipes and idle valves etc.

Now the PCV system of most turbo engines consists of a part throttle breather which has a one way valve that
is open during idle and off boost conditions, so the vacuum of the engine can draw any oil vapor thats formed
through engine motion and combustion, into the inlet and is burnt in the combustion process.
This valve is usually plumbed into the plenum, and is vented from the cam covers.

Now as soon as there is positive intake pressure (boost) this valve closes to prevent loss of pressure, and a second breather which is also from the cam cover and has no valve, takes over the breathing, but this is
plumbed into the intake before the turbo, so there is useually only a sufficient depression when there is boost pressure
being made.

Hopefully this will give you the general idea of it function, so when it comes to fitting a catch tank, most just
block off the non return valve into the plenum, and then fit an extension pipe to the full throttle breather to the
catch tank, and then leave the other opening vented to atmosphere, which is fine in most cases, and will
achieve the desired effect, however some engines do play up when using this form of venting, but it gets a bit
more involved than i want to go into here.

But there is a second way of achieving the same effect, but still using the factory PCV system with a catch tank,
This basically consists of linking both the full and part throttle breathers together, and running them to the catch tank, then linking the second hose from the tank back to the turbo inlet piping, so the same vacuum is applied through the tank to the cam covers when there is sufficient depression, but in this case the oil vapor is still re emulsified into the tank instead of getting drawn into the intake system, ( it helps to fill the catch tank with stainless scouring pads) to aid oil drop out, and with this method you will tend to see less water accumulation too.

So you see there is more than one way to plumb and use a catch tank.

There is also a way of using the exhaust as a PCV system, which i can go into if anyone is interested.
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Old 19-01-2011, 09:52 PM   #2
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Good guide, but now im dead confused as just gonna fit mine within the next few weeks
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Old 19-01-2011, 10:11 PM   #3
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I will try and find some sutable pics that will show the details.
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Old 19-01-2011, 10:13 PM   #4
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That'd be a help mate it really would. Are you giving out advice where to plumb into for free also?? If ya dont ask you dont get
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Old 19-01-2011, 10:43 PM   #5
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Good write up Tricky!

Here is a pic showing one way to install a catch can.

My rocker covers and cam belt cover need to be painted
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Old 19-01-2011, 11:06 PM   #6
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Thanks! i have adapted your pic to show what i mean by the closed system, not to good with paint, but hopefully you get the idea. the tank in this pic is rather small and has a breather in place of a lid, and for large single turbo setups i would increase the size of the hoses and tank.
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Old 20-01-2011, 12:47 PM   #7
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i prefer open breathers.. means no oil vapour covering intercooler pipes. means no octane robbing oil gas in my mixture and a cleaner engine.

whats your views on this..

personally i block PCV
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Old 20-01-2011, 01:01 PM   #8
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I used open on one of my S14s, but i used the closed on my Supra, never had any oil coming back into the turbo intake, some engines like to have the PCV still running, as it avoids seals weeping etc.

I am currently running a closed system on my 350GT, the VQ engine seems to chuck a lot of oil through the breathing system on idle, it works very well, i would say it reduces the amount of vapor going into the plenum by 95%

You do need to fill or baffle the catch can more on a closed system, long pipework helps too, that way you will see very little oil, if any going back into the intake.
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Old 20-01-2011, 01:14 PM   #9
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has anyone used a 'proper' external crankcase breather on the RB (similar to the CA is what i mean) rather than just relying on the block breathing via the head oil drains (which I imagine is a contributing factor to oil starvation in the bottom end at high rpm).

most of the searching i've done just results in a thread saying "if it's breathing that hard, your engine is knackered" which isn't really an answer
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Old 20-01-2011, 01:55 PM   #10
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Originally Posted by alanjuggler View Post
has anyone used a 'proper' external crankcase breather on the RB (similar to the CA is what i mean) rather than just relying on the block breathing via the head oil drains (which I imagine is a contributing factor to oil starvation in the bottom end at high rpm).

most of the searching i've done just results in a thread saying "if it's breathing that hard, your engine is knackered" which isn't really an answer
Not sure what you mean by "proper" its a long time since i saw a CA engine so can't remember, i know the SR has an external equalization to the sump from the head, which IMO is why it gets on so well with running an open breather system.
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Old 20-01-2011, 02:22 PM   #11
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same thing - it's a baffled takeoff from the crankcase itself that goes to the head externally and then to the PCV/intake.

it just seems to be a bit pants to drain the head and have the engine breathing through the same space.
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Old 20-01-2011, 03:52 PM   #12
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Guess it depends on the available space within the engine design, as to whether an external breather tube is needed, i don't think its necessarily a better design, just a case of needs must.
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Old 20-01-2011, 04:44 PM   #13
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how about the GTR then its setup different to GTSt
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Old 20-01-2011, 04:58 PM   #14
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how about the GTR then its setup different to GTSt
In what way does it differ? other than in layout, it still has cam covers vented, and uses the usual part throttle, and full throttle PCV system, so it can be treated the same, its only when higher boost is run from larger turbo/s that its sometimes a good idea to enlarge the std fittings and pipe size.
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Old 20-01-2011, 05:33 PM   #15
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Quote:
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In what way does it differ? other than in layout, it still has cam covers vented, and uses the usual part throttle, and full throttle PCV system, so it can be treated the same, its only when higher boost is run from larger turbo/s that its sometimes a good idea to enlarge the std fittings and pipe size.
on the GTR it has one from turbo to cam cover then one linking cam cover together then one from cam cover back to engine ( above injectors )


so which would be the best way on this engine
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