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Catch Cans? whats the deal

dabigbolf
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Steve Grand Master

Steve

Posted
Posted

PCV is there to stop blow by pressurising the crank case. the reason I believe it would be better to put it through a filter first is that the contaminants in the crank case fumes can be somewhat removed by the process of filtration - so a catch can would be better than just plumbing those gases straight into the plenum. Any contaminents in the gases would effect the combustion process and therefore reduce power and economy - very slightly though, but none the less, would be detrimental. Unfortunatley it is not legal to vent these gasses to atmoshpere, so you would have to plumb them back somewhere.

I do know what you mean about coolers getting coated. I noticed on mine when I fitted a front mount that the intake side was black from oil and contamination - hardly helpful to the cooling process.

All of this would be from when driving on boost, as when not on boost the gases plumb directly into the plenum. The problem is the oil/contaminates that gets suspended in the gas from the crankcase, coat the cooler. Thus the creation of the catch can, or breather if you want to vent to atmo.

A good catch can will remove this contamination, therefore making the only downside to recirculating burnt gasses that there is no oxygen, but at least all the nasty rubbish isnt going directly into the plenum, so combustion would be effected to a lesser extent than if the gasses were plumbed directly into the plenum.

So, in summary, the amount of oil and contamination should be well within the capability of any decent catch can, as it is moving at low velocity, and isnt of a sufficient quantity to have a negative effect on the cooler - this only may happen if the catch can isnt particularly well designed, and when on boost, not when at idle/cruise conditions.

Basically, everything to gain and nothing to loose.

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DennisRB30 Community Regular

DennisRB30

Posted
Posted

By the sounds of it you basically agree with me then (?) You no longer think its a good idea to get rid of the line to the plenum?

Just a few things though.

"PCV is there to stop blow by pressurising the crank case."

The two rocker cover outlets alone would stop this as any pressure could easily escape through them.

"All of this (crap inside the cooler) would be from when driving on boost, as when not on boost the gases plumb directly into the plenum."

True, but only when you leave the PCV system intact like how I discribe, otherwise the crap will go through the cooler at all times (albeit filtered with a catch can)

Look at brownies last drwing or my drawings, the PCV system is still there AND it still filters the gasses that go into the plenum! (the only differance between mine and his, is that mine uses active crankcase scavenging)

In either of our systems you get the benefits of filtering the gasses at ALL times AND you have the benefit of the gasses only going through the cooler sometimes.

Surely thats a good thing, right? I mean, why not do it that way if you can? Thats my gripe.

"Basically, everything to gain and nothing to loose."

Heres a dodgy scenario with figures plucked directy from my arse. I will choose figures that make it easier to understand and might not necissarily be what would happen but the will do to show the point.

(A) Blocked PCV with catch can fitted. Catch can filters 90% of the oil out. But the gasses go through the cooler 100% of the time.

(B) Dead standard system with no mods at all. It leaves 100% of the oil vapour in the gas. But 90% of the time the gasses go straight into the plenum and NOT through the cooler.

In that scenario the potential for clogging the cooler is the SAME for the catchcan system with blocked PCV line, and the standard system. The contaminents in the vapor are much less with the catch can system, but they flow through the cooler much more often. The benefits tend to cancel eachother out somwhat no matter what figures you use.

The catch can system is still better than stock because, the OVERALL amount of contaminents that reaches the ENGINE will still be 90% less than stock. But the amount of contaminents that will reach the COOLER will be similar.

© Catch can fitted with PCV intact, see brownies last pic or my pics. You still get ALL the benefits of (A), and you get ALL the benefits of (B). Would you agree that in that case there realy is everything to gain and nothing to loose?

Steve Grand Master

Steve

Posted
Posted

Agreed filtering all the gasses would be ideal, (well nearly, venting them to atmo would be ideal, but illegal) and have them go through the plenum when not boosting, instead of the cooler, is better than having all the gasses go through the cooler all the time.

Just think that for the work involved, as the amount of contamination of the cooler from cruise idle blow by would be miniscule, versus blocking the line from the rocker cover to the plenum - just not too sure it would be worth the extra buggerising around and the extra hoses 'untidying':) the engine bay. For me anyways. I like to keep things neat.

Wouldnt it be easier to have two catch cans, one before the air intake, one between the rocker cover and plenum? - would be alot neater ;)

  • 1 month later...
MM2death Grand Master

MM2death

Posted
Posted

Thanks guys...

Paul,

The catch can you are talking about. Is it one line in, and one line out (back to intake) and this line carrys just air not vapour. Correct?

The can i showed in my beautiful diagram was two lines in...and then just a breather at the top. But yeah like Steve said only one line really needed.

Dennis,

it only looks like i'm banned. :)

Thanks again,

Scott

  • 1 month later...
Guest MrEscortCosworth

Guest MrEscortCosworth

Posted
Posted

oil/air seperater are legal if they do recirculate, and not vent to the air.

if your a smartassss to the cops they will pick on you and most of us dont know the law that well so they get away with a bit. i was under the impression that they are not allowed to look under the bonnet but hey, whats gonna be illegal, just make sure it all looks good and recirculate your bov, cos thats the main thing...

regards Anthony

  • 1 year later...

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