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On the street both sides vented is fine. On the track people were getting excessive oil out of the intake side so it is common practice to cap that side and run just one -10 hose off of the exhaust side to a vented catch can.
I'm adding Radium catch cans in line with each of my crankcase vent lines in anticipation of possible blow-by with boost. Figuring out all of the lines/fittings/etc. now and was pondering how I wanted to do the PCV line; specifically, since factory PCV valves often do not properly/completely seal when the intake manifold sees boost I was planning to add an in-line check valve between PCV valve and IM to prevent back-flow on that line. Then I saw Radium recently added a fancy PCV valve that mounts to their catch cans and that's supposed to be specifically designed to handle reverse-pressure under boost: PCV Valve, 10AN ORB to 3/8" Barb Radium's stuff is generally very good but this valve is an unknown to me.
If it performs as they say this would eliminate the need for a separate in-line check valve, and it can flow a larger volume of air than the factory PCV which is notoriously under-sized.
On the topic of boost, PCV and check valves, my built MSM is running 20psi on the street, 14psi on the track. I want to keep the PCV valve as I do a fair bit of street driving but I am also aware the PCV side is known to puke pure oil on track so will run a mishimoto compact can inline. What small sized check valve are people using? Will a generic brake booster valve be fine? (prefer something metal, not plastic). All I can find is fuel line one way valves and they look huge.
The 1.6 L and 1.8 L B series blocks were developed for Mazda's front wheel drive rally car entries, and homologated by selling in the 323 GT turbo, and later in the Ford Capri turbo.
They prepared for the high boost in the rally cars with crank case ventilation from the side of the block and an oil return to the FWD oil pan. On street cars they still placed the fittings, but just capped them off. The early short nose Miata engines still have those ports in place, while the later engines and the BP have the landings on the block, but where not machined open.
Their design has an advantage that the over pressure does not have to pass up the return oil galleys (and the returning oil from the head) in order to be vented, which should reduce some of the air/oil aerosol formation. original Mazda crank case vent beside oil filter . . The Mazda-made hole viewed from the inside in an empty block. Oil return to FWD pan sump
I ice race a 1.6 L turbo and had a lot of trouble with blow by at about 10 psi boost. The vent from the head (not the PCV side) spewed about 1 L per 15 minute race into the catch can. I had the engine professionally rebuilt and it still did it. I re-ringed another block and it still did it. So I decided to use the original Mazda approach, took the caps off, and attached a Moroso air oil separator/breather vented to atmosphere. It works very well. I now collect about 100 mL per race from the head catch can, and it is such a frothy mess I would not want to return it to the sump, or to the intake manifold. (The passage in the head is filled up with steel wool, but it does not seem to change all that much.) Pay no attention to the necklace on the separator! It is dryer vent to shield it from ice and snow.
I am refreshing a new engine, from a JDM 1999 Miata 1.6 L. It has the lands on the block, but the ports were not opened up. So last weekend I took the block to my friend (and competitor) who owns a machine shop and he drilled and tapped a 3/4 " hole and I put in a -8/-10 AN adaptor to connect to the catch can. A bit scary but it turned out well. The next step on a Miata would be to port the oil pan below the oil level, but I am putting the FWD oil pan on, which already has the port.
drilled and tapped, great care was taken to collect the fragments of steel. -8 AN o-ring fitting, with -10 AN thread for hose
I have started on building a turbo Miata 1.8 L, and plan to get the same machining done on that block when the time comes to race it. The ice race engine will be the test on the AN fitting and how clean we managed to be in the drilling!
Icedawg, I follow the part about the block vent, but not the part about the oil return. Return from where?
The Moroso oil separator catch can has a return drain to send back to the sump. You can see the brass fittings for the return at the bottom of the catch can picture.
Oh. The head (valve cover) catch can you do not return. A separate catch can from the block, you return to the sump. Is that correct?
DNM
Yes the crank case ventilation goes to the Moroso air/oil separator, and the oil returns from it to the sump.
I have a separate catch can on the vent off the head, and that simply catches anything that still makes it through, and collects it in a catch can. The stuff off the head is frothy, and smells more of exhaust and gas than oil.
Funny, I had a similar idea of venting front the valve cover's driver side to a catch can which has a second port connected to the intake pre-turbo. A third port at the bottom returns the oil to a Y fitting in the 10AN turbo oil drain.
On the topic of boost, PCV and check valves, my built MSM is running 20psi on the street, 14psi on the track. I want to keep the PCV valve as I do a fair bit of street driving but I am also aware the PCV side is known to puke pure oil on track so will run a mishimoto compact can inline. What small sized check valve are people using? Will a generic brake booster valve be fine? (prefer something metal, not plastic). All I can find is fuel line one way valves and they look huge.
The generic brake booster valve (in my case off a honda) works well. I tested one with the air compressor at 40 psi, it held the pressure, so I've been running one a little over a year.
Funny, I had a similar idea of venting front the valve cover's driver side to a catch can which has a second port connected to the intake pre-turbo. A third port at the bottom returns the oil to a Y fitting in the 10AN turbo oil drain.
That is similar, and using the turbo return line is an interesting idea.
The oil return from a vented catch can is supposed to be below the top of the oil in the sump. If it is above, the return instead acts as a second vent port to atmosphere, and pushes the returning oil back up towards the can.
Your arrangement would have that problem, except the oil returning from the turbo is being pumped, so should flow against the blow by pressure and into the sump anyhow.
Then the returning oil from your catch can is probably entrained in the turbo oil flow, and is not forced back up either.
With the setup where both vents are connected to a vented catch can.
Do you have to change the PCV one way valve into a normal fitting instead? (and you have to tap a new AN fitting to it?)
Since without manifold vacuum，the one way valve could act differently?
But I guess if the pcv is vented to the atmosphere(catch can), it would be similar to WOT, where intake manifold would be at almost atmospheric? and the PCV valve would open fully?
The rush of gasses upward through your proposed "drain" will blast oil into your catch can.
MSMs had a similar problem when modded on fast/hard corners.
Oil would actually find its way into being recirculated into the intake, through the intercooler, TB and intake manifold (easy to see by removing the coldside intercooler pipe connected to the intercooler barb and finding a pool of oil in it).
FM sell a one-way check valve to prevent this: MSM CHECK VALVE KIT
08-07-2019, 05:20 PM
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