I'm interested to see this dual catch can system. I'd also like to know how much it would cost to buy all the parts for it.
I 'm currently running Prodigy's catch can on the breather side of the system only. The PCV side is still connected through a check valve to the intake manifold. I'm not concerned about any unburnt fuel, water, etc draining back to the oil pan because it will evaporate again and get sucked out through the PCV hose when I'm not on boost.
How much oil are you actually catching on the PCV side? I assumed that I shouldn't need to worry about catching oil on that side because the engine should already have a decent oil separator prior to the PCV valve. Air will only flow through that side of the system when not on boost, so it shouldn't really be any different than stock as far as how much oil passes through and how bad it is for the engine.
Have you noticed any improvements in off-boost driveability after adding the catch can on the PCV side?
The check valve is necessary to avoid exposing the PCV valve to boost. The PCV valve was not designed to act as a check valve against boost, and it may even leak boost into the crankcase.
Check out part #7775K13 in the McMaster-Carr catalog (in the "Quick-Opening Brass Check Valves" section): http://www.mcmaster.com/#catalog/120/506/=vsmsyx
It should be a direct replacement for the check valve originally provided by Prodigy (same thread size, etc.), but it cracks open at lower pressure (0.3 psi vs 1 psi). This check valve should allow the PCV system to work more closely to the way it was designed to work.
Because of the pressure drop across the intercooler. The intercooler becomes more restrictive (more pressure drop) as airflow increases (higher engine speeds). If your boost source is before the intercooler, boost at the intake manifold will taper off quite a bit at higher rpms. A boost source after the intercooler will work the turbo harder at higher engine speeds to try to maintain more steady boost all the way up to redline (more high rpm power!)
More about this here: http://www.miataturbo.net/diy-turbo-...eed-ebc-47532/
And this post explains why you shouldn't use the intake manifold as the boost source: http://www.miataturbo.net/diy-turbo-...32/#post574757
The results can vary based on whether the engine is warmed up or not. My incorrect BOV spring allows the BOV to crack open at about 15" vacuum. When I first start my engine when it is completely cold, it initially idles at high RPM for a few seconds with less than 15" vacuum, and the BOV is fully closed. As the idle speed drops down over the next several seconds, vacuum increases and the BOV partially opens. It seems to idle at slightly higher than normal RPM for quite a while until the engine completely warms up. At this point I see about 18.9" vacuum. Once it is fully warmed up, I see about 19.8-20.1" vacuum, and the BOV is fully open.
I've determined I have the "WHITE" BOV spring (spring chart: http://www.tialsport.com/documents/w3_tial_qqr_sp.pdf). I have talked with tech support and concluded that the "YELLOW" spring will most likely be just a bit too much and cause some compressor surge. The "PLAIN" spring is a bit too weak and may allow the BOV to crack open at idle when the engine is fully warmed up, but it will respond quickly and avoid compressor surge. My plan is to install the "PLAIN" spring and fine-tine it with a couple washers to shim/pre-load the spring enough to keep the BOV completely closed at idle.
If you want to find out what spring is in your BOV, you don't have to open it up to find out. There's a serial number on the top of the BOV. I was able to read it with a small mirror without removing any parts from the vehicle. It starts with the letters "SN", so that will help you identify it and calibrate your breain to read the numbers backward in the mirror . You can send the serial number in an email to tech@tialsport.com and ask them which spring they put in it.
BTW - Prodigy confirmed that they order BOVs with the "PLAIN" spring. Not sure how I ended up with the wrong spring.
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