crank case pressure question

Post by **Bwana** » Tue May 19, 2009 5:01 am

I'm going to go ahead and respond here with some practical findings regarding exhaust evacuated pcv systems.

I installed one on my rb25 powered coupe a few months ago. The car has a gt3076r on it, external wg w/ screamer pipe and a custom 3" dp w/o cat going into a apex-i gt ss exhaust. This = absolute minimal restriction. I have the pcv routed in near the back of the dp. The system seems to work well under MOST circumstances (though I haven't tested it with gauges or anything) but I do know for a fact that has caused pretty significant smoking on deceleration which has influenced me to change it back.

Post by **r34 gtr** » Tue May 19, 2009 6:40 am

Bwana wrote:aused pretty significant smoking on deceleration

I mean, I would just assume that if one was to dump oily fumes in the hot part of the exhaust that it would smoke. Correct me if I am wrong.

Post by **Bwana** » Tue May 19, 2009 7:30 am

I think it would, but on decel I think the problem is there's insufficient exhaust flow to create the necessary vacuum to evac the crankcase so the high cylinder vacuum is pulling oil past the rings, resulting in foul smelling and unsightly smoke billowing out of the exhaust...

Quite undesirable.

Post by **r34 gtr** » Tue May 19, 2009 1:10 pm

I don't know about that, as I was just running my Exh side breather into the intake side, and then into the intake manifold, and it never smoked much at all, if any.

Post by **bentvalves** » Tue May 19, 2009 3:32 pm

yea thats the line Jbsuper- remove that metal pipe that tapers down there under the plenum as you wont be able to plumb the lines proper.

this setup is an awsome solution if you are filing catch cans during hard driving.

Post by **dash** » Wed May 20, 2009 5:37 am

any pictures with this 'sr20' can installed/routed ?iirc, blockage in "metal pipe that tapers down there under the plenum" is the major source of the CA18 breathing problems ?

last entry of the 12.2sec fwd pulsar only had one puny filter venting his cam cover.Said that was a "fresh" motor he was flogging tho - lol Amazing what some CAs get away with

Post by **bentvalves** » Wed May 20, 2009 6:54 am

I think all high boost CA's suffer from blowby, and I believe that metal pipe under the plenum that tapers in a hard 90* bend was nissans simple solution to trying to keep oil down in the case. The 90* bend simply made it a bit moe difficult for oil to get up into the head.

I can get some pics up of the SR can behind the intake manifold of a CA for reference if anybody is truly interested. Slight fabrication is needed to orient the inlet/outlet properly, please bear this in mind.

Post by **sjbsuperman1425** » Wed May 20, 2009 10:43 am

definately interested.

also, could the KA can/box be used?

i guess im still kind of confused on how this helps or whats going on with the metal pipe, oil, and breathing problems..maybe im just reading something wrong

Post by **bentvalves** » Thu May 21, 2009 3:45 pm

the box on the side of the KA block behind the alternator?? nah dont use that, wont suffice. Heres some pics, my finger in the pictures shows where I will relocate the inlet/outlet.

I currently fill catch can during hard driving without this box, but have it draining back to pan. I have to be standing on revlimiter for like 30 seconds at a time to get it to puke out the cans breather cause it cant drain back quick enough via a -8.

Post by **bentvalves** » Thu May 21, 2009 3:47 pm

holy balls those pics are huge, I dont know how to downsize them though.

Post by **The_Chosen_One** » Thu May 21, 2009 3:52 pm

I can powder coat that bish.

Post by **bentvalves** » Thu May 21, 2009 6:41 pm

lol iiii knooowz you can Julian : )

Post by **sjbsuperman1425** » Fri May 22, 2009 3:31 pm

ok, i understand the SR20 can is to help it breath, but what is it doing to make the engine breath better? what is the SR20 can doing that the dual catch cans up top are not doign? i just want to understand whats going on.

Post by **bentvalves** » Fri May 22, 2009 6:31 pm

ca's are notorious for puking blowby gasses/oil through the breathers wherever you have them routed. Since you apparantly are not filling catch cans with oil, or puking massive amounts of blowby into your turbos inlet, the sr20 can is not a route you need to be worried about.

the can keeps oil down in the crankcase, and lets the head breathe air not oil.

Post by **sjbsuperman1425** » Sat May 23, 2009 1:08 am

ic ic..i must have not read everything good enough lol thanks for clearing that up ks

Post by **sjbsuperman1425** » Wed Jul 15, 2009 5:53 am

ok, woke up thinking about this.

Is there a difference between putting a regular oil catch can vs the SR20 can in that spot?

Post by **Ca_Silvia** » Wed Jul 15, 2009 6:04 am

No, therory behind the 2 are the same. You will simply have to empty the catch can when its full.

Post by **bentvalves** » Wed Jul 15, 2009 9:20 am

the sr20 can is not a catch tank, but an "equalizer" so to speak. You would still use a catch can in conjuction with the air/oil equalizer, or just as the SR does OEM, run a breather pre turbo.

The can is simply keeping massive amounts of oil getting up into the head in the first place. Boost pushes its way past piston rings, down into crankcase, and pukes oil up into the head via the block breather ontop of the oil filter housing.

This is where the SR breather box steps in and keeps oil down in the crankcase.

Post by **D_Stirls** » Wed Jul 15, 2009 11:16 pm

IMO the problem with the CA crank case pressure is caused by the fact that the pressure return pipe that runs from the crank case to the head is too small. It starts off at a good diameter but then reduces to a -8 size after the 90 degree bend and causes a restriction. To get around this when i rebuild my engine i'm going to double can it; there will be one can for the crank case that will run a -12 line and have a big filter that will vent the pressure without causing a restriction, this can will be mounted under the intake manifold and won't be seen unless your looking for it. The second can will be the same as what i'm running at the moment. This isn't legal interm of emissions but to make it legal (if i ever need to get it inspected) i will just remove both the filters and run lines to the intake. But i have a lot of other defect/compliance problems that will have to be changed as well.

Post by **bentvalves** » Thu Jul 16, 2009 2:36 am

if the "pressure return pipe" as you have called it was any bigger in size than it currently is, than the amount of blowby gasses/oil making it to the head would be even greater.

Post by **D_Stirls** » Thu Jul 16, 2009 3:12 am

What do you think that pipe is for? It isn't an oil drain, they are internal.The gasses have to go to the head, the only way for the engine to release excess pressure that is produced is through either the PCV when the plenum is in vacuum or through the exhaust side breather when the plenum is under pressure. So for the pressure to get to the head is has to go through the equalisation pipe that runs from the crank case to the head.

Post by **Ca_Silvia** » Thu Jul 16, 2009 5:01 am

D_Stirls, did you just block off the PCV? Any smoking at idle, decel or boost?

Post by **D_Stirls** » Thu Jul 16, 2009 5:05 am

yep just unscrewed it and screwed in a blanking plug. No smoking but the compression figures for the engine are very good (165psi across the board), this doesn't help on decell' though but i have never had any smoking problems.

Post by **bentvalves** » Thu Jul 16, 2009 8:30 am

correct, it is not an oil drain. Hence me saying if you made the diameter larger, more amounts of blowby (oil) will have an easier journey TO the head. Boost pressure as I stated before makes its way past the piston rings, down into the crankcase resulting in blowby gasess/oil being puked back into the head via the pipe with the hard 90 on it.

Post by **niscort** » Thu Jul 16, 2009 12:11 pm

ks13 wrote: Hence me saying if you made the diameter larger, more amounts of blowby (oil) will have an easier journey TO the head. Boost pressure as I stated before makes its way past the piston rings, down into the crankcase resulting in blowby gasess/oil being puked back into the head via the pipe with the hard 90 on it.

Easier journey to the head? So by restricting this 'path', you figure you can reduce blowby? The only thing this a restriction will do is create a greater pressure in the crankcase, which is what crankcase breathers are designed to alleviate in the fisrt place.

Blowby is blowby, if youve got it... fix the cause not the side effects. you cant reduce or restrict it.

other comments... I see no point what so ever in removing the PCV from a boosted setup. The PCV is there to serve a purpose, which is to flush the crankcase with 'fresh' air.

Draining any oil from blowby/vapour back into the sump is also not a good idea.

Post by **sjbsuperman1425** » Thu Jul 16, 2009 2:27 pm

i just got a Top Fuel oil catch can from my friend and am going to fill it with steel wool and route it like the setup with the SR20 air/oil separator. hopefully everything turns out ok?

Post by **bentvalves** » Thu Jul 16, 2009 4:33 pm

agreed on PCV sentiments.

draining catch tank back to oil pan isnt the best idea, but I change my oil frequently enough and for now that setup will have to do untill I get the SR air/oil equalizer plumbed properly on my next motor.

Post by **sjbsuperman1425** » Sat Jul 18, 2009 6:40 am

installed the oil catch can yesterday on the turbo side only (got lazy). everything runs great, but i noticed when taking off the stock hose, that there was some sort of check valve in it up by the valve cover, but now i dont have one. should i get one, or am i ok?

Post by **BQ.05.TD** » Sat Jul 18, 2009 3:43 pm

so say i want to use one of those crankcase evacuation system on my street car with a muffler and a cat, how well would the 1 way valve work you think? beeing that it will be driven on the street every day. i dont care about the legalities of it. just want to know is this would work on a street car and not just a race car

and could you put one of the lines directly to the block breather and the other one from the pcv line then just a little filter on the exhaust side to draw in fresh air?

Post by **float_6969** » Sun Jul 19, 2009 6:40 pm

sjbsuperman1425 wrote:installed the oil catch can yesterday on the turbo side only (got lazy). everything runs great, but i noticed when taking off the stock hose, that there was some sort of check valve in it up by the valve cover, but now i dont have one. should i get one, or am i ok?

It's not a check valve, just a restrictor. You're fine w/o it.

crank case pressure question

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