This is how my car's catch can came routed. The upper nipple us connected to the catch can, which is vented to atmosphere. The lower hose goes straight into the intake before the turbo.
This leads to a managable but annoying amount of oil getting into air filter, the intake piping, etc.

Is there some reason I couldn't cap off the bottom nipple and run a hose back from the catch can to the pipe going into the intake?

Or would a single stock nipple (hooked to an 6 mm ID hose) simply not be enough crankcase ventilation?

I only have two 6m ID (9 mm OD) nipples on the catch can, so doubling up hoses to the catch can wouldn't work without changing the catch can.
Unless I replace the current nipples with much bigger ones (9 mm ID should suffice), and then use a Y-fitting. Then I could just eliminate the hose to the intake entirely.
That wouldn't be a very elegant solution, though.

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I suppose I could also buy a used oil filler cap, chop off the stock nipples, and thread in a much larger hose fitting, and then run that to a more substantial vented catch can.

 

funny, I was just thinking about my filler neck today, particularly trying to get more 'flow' out of the breather. Without replacing the entire neck with a pricey aftermarket one, has anyone tried drilling and tapping the square boss that the upper filler fitting is attached to, and perhaps getting a 1/2" NPT port in there?

edit: sorry just saw your last line under the pic. so is cutting and tapping like you suggested a somewhat common modification?

I was also considering just leaving the two ports uncapped and open to atmosphere because I'm just grubby like that

 

I don’t know if anyone has done this. I was just looking at a picture of the stock neck and wondered if it was possible.

I’ve seen pictures of cars that had a big hose fitting straight through the filler cap, which would work but isn’t very elegant.

I don’t recommend venting them directly to atmosphere!

 

that second hose, the lower one that goes right to the front of the turbo is essentially how Mazda did it.

 

Right, my question is essentially do you need the full ~56 mm2 of ventilation (2x 6mm nipples) or would half that suffice. I’ve seen pictures of people who capped off the lower nipple, but it doesn’t mean it’s necessarily a good idea.

 

You don't need both. Just the one is fine. You can leave the lower one just vent if you wanted. You just need to cap it or something when pouring oil in but you don't need to run a vacuum line off it to anywhere

 

Fellow here put his catch can in series in the venting hose to the front turbo intake.

He then overfilled his oil and ended up with his intercooler half full of oil.

But he reported the catch can was dry.

Our guess was that: if the oil overflowed into the catch can it then got vacuumed out into the front turbo.

 

can someone educate me on why the PCV is routed the way it is?
so the upper nipple on the oil filler goes to the plenum via check valve, presumably it sees vacuum when off boost
then the lower nipple is connected to the inlet pre-turbo. so it sees a vacuum under all driving conditions
so the 'crankcase' is being vented via two ports when off boost, but when on boost, only via the pre-turbo pipe.... why?

 

should hook the oil filler vents to the charcoal cannister return line... free premix

 

Errrrr...wromg type of oil. But you know that.

 

Presumably, the intake provides fresh air to the crankcase when there is full vacuum in the manifold, and it provides vacuum to evacuate the crank case when the manifold is under boost.

I think a slight vacuum in the crankcase is considered ideal.

 

I bought a generic catch can with a brass filter and a baffle from Aliexpress that will fit in the same location as the original.
I'm going to just plumb it in series, but with the breather instead of a closed system. This should reduce the amount of blowby that ends up in the intake.
I figure the worst case scenario is that the dipstick pops out. In that case, I will look into a installing bigger lines and fittings.

 

First off, if you are street driving, maybe some trips to the Dragon, you don't need to go nuts on a catch can setup IMHO. I've had the same catch can setup for probably 15 years and have had zero problems - it doesn't fill up super quick, everything works perfectly, zero issues.

I have a catch can with a breather (it's an old Jaz catch can that I don't think is made any more) and it has 2 nipples, I have both of the stock oil fill nipples running to it. That's it. Zero issues. I clean out the catch can on an oil change and there's usually a bit of junk at the bottom but not much.

If you routinely do track days that's a whole different story - doing sustained very high G forces in turns can do weird things to oil. Besides that, my setup will be just fine.

There is no reason to use the stock PCV valve or vent anything to the turbo inlet.

Dale

 

Personally, I’ve only had my catch can fill up on track days when my oil was overfilled.

 

What Dale said. If you're not doing track days on R-compound tires, don't sweat it. The little JAZ breather hooked to a stock filler neck as Dale outlines is all you need (they still make it):

https://www.jazproducts.com/store/1-pint-mini-breather

I'd suggest the "natural" vs the black, so you can easily see what's in it.

 

He is doing track days though

 

Well, I re-routed mine recently, and I'll get some track results on Friday. It's the larger 1qt. JAZ can. I had a custom neck made, one -12 (to the JAZ can), and two -10's, (one from the rear turbo drain, and one with a PCV to the UIM). Stay tuned.

 

I just saw this today https://www.radiumauto.com/products/...azda-rx-7-fd3s

 

On super-200s, rather than r-compounds, though.
Things might be different if I went to some A050s.

 

It's really interesting, but I don't get where excess oil would go once full (which would happen quickly). Does it go in the brake booster? It also doesn't vent to atmosphere, so where is it venting while the car is in boost?

 

The instructions made no mention of capping off the lower of the two nipples on the oil filler neck, so I guess it's still got a little vacuum pulling on the system even under boost?

Presumably, there is a check valve between the intake manifold and the catch can. There would be a LOT of boost going into the catch can otherwise.

You can buy a dozen catch cans from Alibaba for the cost of this kit. lol.

 

In the Radium can, there is a float ball that closes the inlet if the can becomes full. Also there is a check-valve so the can only sees vacuum. My understanding is that the other nipple on the filler neck should still be routed to the air filter or another can.

 

At only 7oz fluid capacity, I think you're putting a lot of fluid in wherever that overflow is going to. Especially as this doesn't enlarge lines or really "breathe" the crank case out at all. Will be interesting to see if anyone installs it.

 

I ended up buying one after looking at it. Ill post pictures when it comes in.