M35 Wot Smoke, Pcv And Catch Can Setup

[Equilibrise]

So lately i've been researching crankcase ventilation and as there is not much posted about M35's I thought i might start a discussion about it.

As long as i can remember, i have had a bit of a cloud of smoke when ever i dump it when the rpm is in the higher range. I have found that the cause of this is inadequate crankcase ventilation and evacuation.

The stock system is probably ok for a stock car but once the car is a bit modified and power is increased and especially if boost pressure is increased, then the stock system cant keep up. So here is how the stock system works:

ALL engines produce some amount of "blow-by" (which is basically a mixture of oil, oil vapour, unburnt fuel and hydrocarbons - or exhaust fumes) which is 'blown by' the piston rings and end up in the crankcase. As this continues happening as the engine runs, it builds pressure in the crankcase. This horrible mixture then makes its way up to the heads. Originally and even in some cases now people vent it to the atmosphere through a "breather" filter, however it is now not emissions legal and it stinks and it doesn't create a vacuum to suck the blow-by out of the head.

For it to be emisions legal it must be recirculated through the intake and re-burnt. It also actually lowers the octane of fuel, but depending on how much blow-by your engine creates depends how much octane is reduced. The stock setup does this via a PCV (positive crankcase ventilation) valve which is basically a oneway or check valve with a spring in it so that it opens differently to different amounts of vacuum. Under strong vacuum (eg, idle) it is slightly open, under medium vacuum (eg, throttle open but not boosting) it is completely open, and under pressure (eg, boosting) it is completely closed. It is located on the front of the right rocker cover and has a vacuum line running to the manifold. Even with a stock setup this should and is meant to be replaced every 100,000kms, as if it blocks, spring stretches, gets sticky or fails completely then the motor suffers and you can end up blowing seals, smokey exhaust, poor fuel economy and much more.

Before the blow-by evacuates through the PCV it passes through a series of baffles in the rocker covers in an attempt to separate air from oil. As the PCV is not open all the time and even at the most important times (eg, under hard acceleration) the motor must vent the pressure somewhere. On the VQ25DET there is a vacuum line running from the back of the left rocker cover to the intake before the turbo but after the air flow meter (MAF). This line also has a oneway/check valve in it to only let pressure out. The intake before the turbo is always under vacuum which assists in evacuating the heads building pressure. The only time fresh air is taken in is when the intake manifold is in light vacuum.

There are many ways to evacuate or relieve the pressure. Some are expensive and some are cheap. Most use an oil catch can which is made as an oil/air separator to catch the funky mixture so that it doesn't re-enter the engine and can be drained and discarded.

Another point to consider is that it is apparently better for the crankcase to be under vacuum, rather than pressure, as it supposedly helps seat the piston rings better providing a better seal and therefore less blow-by and better combustion.

So, below is a pic of how i have done mine. I have a small filter on the intake line for the head, so this does actually introduce unmetered fresh air into the intake, but only on idle (which i don't mind). I have drilled out the PCV, removed the check valve at the back of the motor and introduced new check valves (which you can see in the lines - they are silver). I have also installed baffles in the catch can so that it actually works as a catch can. So the check valves allow vacuum from the manifold but close when its in positive pressure when vacuum is then introduced from the pre-turbo intake. I'm not saying everyone should do it like this and i'm sure there are probably better ways, i just thought i would put out some more info. The end result is that it works! No smoke out the back at any time and the car runs a little better.

Just my 0.02c. What do you guys think? More input from more experienced m35ers?

[Equilibrise]

And please don't laugh at my engine bay. I can only afford what works, rather than what is pretty...at the moment.

[PN-Mad]

Thankfully it's much easier on a vq35, as mine just adds a catch can between the PCV and the return to the manifold.

Often overlooked is whether the can actually contains anything! Lots of the cheap cans have no baffling nor contents inside. Meaning, it's basically useless. I have a fairly large can, and it's stuffed with about 5 expanded stainless steel pot scrubbers! This provides the scrubbing action to remove oil from the normal crankcase gasses. Works really well. The crap doesn't build up in the manifold or the back of the throttle plate anymore.

[Ben C34]

On all cars you can simply add a catch can (seperator) onto the line returning to the pre turbo inlet. And leave everything else alone.

The blowby doesn't go into the manifold through the pcv, as it's shut when under decent load, and under low load there should be very little blowby to worry about.

[PN-Mad]

Then you should have a look under the plenum of a high km vq35....

It's not nice. There is lots of oil in the gallery's that lead to the runners, and it covers everything in there.

[Lakes101]

Equilibrise what catch can is that your running?

[Ben C34]

Then you should have a look under the plenum of a high km vq35....

It's not nice. There is lots of oil in the gallery's that lead to the runners, and it covers everything in there.

That typically doesn't come through the pcv. A catch can on its own would sort it

[Equilibrise]

Yeah i stuffed mine with stainless wool too Alex.

Nathan, it is an Auto one cheapo. The catch cans that work (ie with baffling) are rather expensive.

Thats right Ben, but a catch can on its own wouldn't create continual vacuum, which is what i was after. I had a catch can on its own but still experienced the WOT smoke.

[Equilibrise]

I had a catch can in Ben's suggested location on my R33 and had no troubles what so ever. It worked well which is why i did the same on the M35 - didn't work well. I'm guessing the combination of high compression and high km's (wear) is what makes the VQ25DET want to ''breath'' more

[Equilibrise]

Also, catch cans should fill up on any car. If it doesn't fill up, then it is not installed properly or doesn't have baffling to separate the vapour. If it fills up too quickely then you have other problems to worry about.

[scotty nm35]

My catch can only ever has moisture and ethanol fumes, hardly any oil. I guess it has nothing to do with power or boost and more to do with bore wear.

It did always blow a little smoke each morning, just oil from the pcv leaking down inside the plenum and sitting on an intake valve overnight.

[dRey]

why in your photo actuator closed all time? or perhaps you use boost controller.

[scotty nm35]

Boost controller I suspect. The stock solenoid is best left plugged in electrically, then remove the bleed T and insert the controller.

As the wastegate actuator is only 7psi it may be hard to hold any decent boost in the top end without getting a stiffer spring for the actuator, to hold the wastegate puck shut better.

[iamhe77]

For what it's worth, I ran two catch cans on my VQ25det Stagea. One on each bank of course.

The intake side never required changing as there was never really anything in there.

The driver side (PCV if my memory serves me) however, caught quite a bit of oil.

[Reprieve]

Sorry for digging up an old post, but just curious as to how this setup doing after almost a year?

[scotty nm35]

I wouldn't bother with catch cans, my engine never spewed oil, even at 8000 revs and 40psi at the track. Emptying it is just another thing to worry about when servicing, let the moisture and vapours burn I say.

[m35stagea]

Only turbo car i have had that nothing comes out havnt even had moisture personally.

I dont think its worth theeffort required on a vq.

[Lakes101]

I got about 200ml of oil out if my catch can last time I emptied it, it was a good 4 months that It had been since but still seems like a fair bit of oil for four months of running it. I have put a new pcv valve in about 1 month ago see how it goes with that till next empty