Hi all, i've read through all the informative Catch Can solutions, particularly for the Twins setup. Every few years a novel idea arrives, here's my attempt, hopefully it's not DOA, and leads to some discussion.

TL;DR, use:

• Improved Racing DCV-06 Dual-Source Check Valve
• Improved Racing CCS Venturi Catch Can (single in/out) or any single in/out, Radium, eBay, Mishimoto, etc.

if i understand correctly, the 2025 'secret sauce' is the DCV-06 (Dual Check Valve). Connect two vacuum sources — the intake manifold (UIM) and the turbo inlet (pre-compressor) — to one crankcase outlet, and DCV-06 automatically selects the strongest vacuum source while blocking boost. So:

• At idle/cruise, DCV-06 uses manifold vacuum.
• Under boost, DCV-06 switches to the turbo inlet.
• According to specs, DCV-06 can handle 300 psi and has a 0.04 psi cracking pressure.

No T-fittings, no “dual catch can”, no venting to atmosphere.

Well, let me know, maybe this idea has already been hashed out. thanks!
-Ed

Rudimentary diagram:

Cutaway view from IR site.

 

This is very similar to what I did with two separate high end check valves with low cracking pressures. I would add the M/E Wagner PCV valve (two stage PCV) or some other type of control to adjust the amount of vacuum used to ventilate the crankcase from the UIM. You don't want to have a larger vacuum leak by using an uncontrolled larger diameter hose from the UIM. The whole system works very well. I didn't know about the dual check valve you are using at the time I did mine. It looks great. I used both filler neck bungs to get cross flow through the filler neck to remove condensation buildup and fumes constantly.

Here is the thread from about one year ago where it was discussed. My post is #35.

Vacuum with oil catch can? - Page 2 - RX7Club.com - Mazda RX7 Forum

Mike

 

Hi Mike,

Yeah, great setup you have going over there, looks like you found the Improved Racing PCVs too! I did consider that or a similar style as well, using their "Dual inlet / Dual Outlet" Catch can here: https://www.improvedracing.com/high-...-can-12an.html (the dual outlet is an optional add-on),

then going with high rated PCVs too. But then, kept digging through the site, and found the DCV-06.

Just about to order the components, it'll be a while for the install, but i'll drop a pic once completed!

-Ed

 

Any reason not to vent to atmosphere?

Also to correct a misconception - the pre-turbo inlet has NO VACUUM. It's atmospheric pressure. Yes, air is getting sucked in but the amount of vacuum if any is VERY small.

I've run a simple Jaz catch can for years - zero issues. There's a whole different world of catch cans if you do track time, but for street use and even driving the Dragon my catch can setup has been perfect. No mess in the intake tract, no smell, no smoke, easy and foolproof.

Dale

 

I was wondering the same thing. Unless you spend some serious track time with sticky tires pulling some serious lateral G-forces, a simple open air vented catch can will work just fine. I'm running a single turbo, so I'm running a smallish vented can (maybe a pint capacity?) similar to Dale's that is plumbed to the oil filler via a -8AN hose (1/2" ID) & matching fitting on the filler neck. Works well on the street and on light track/Dragon use duty (i.e., street tires, sane G-forces). With this setup I find very little oil/liquid will accumulate, maybe an ounce or two every six months or so, and no oily brown crud accumulation on the bottom side of the oil filler cap. That's how I know the sump is breathing well and crankcase gasses are being vented out & moisture is being evaporated out properly. The key I think is having a large enough ID size line to your can so it doesn't clog with liquid oil/moisture and allows vapors to easily pass thru.

 

I believe a vented catch can works ok, but you limit the actual intent of the pcv valve. If you vent the system, you decrease the effect of the uim vacuum due to the venting. In my setup under vacuum, you are constantly sucking fumes and moisture out of the oil filler neck and therefore adding to the crankcase ventilation in addition to the typical pressure relief. In a vented catch can, the flow is very limited since it is an open circuit, but it does relieve any pressure. Under boost, the uim path is stopped by the check valve and the pressure goes through the catch can catch and oil and is vented at the turbo inlet. Indeed, as Dale and others have said the amount of vacuum at the turbo inlet is minimal. Once off boost and back in vacuum, my setup causes rapid evacuation of any blow by in the crankcase due to the closed circuit under vacuum. If an open vented system, this would be much less effective.

Theoretically, my setup will help the oil remain fresher since potential moisture and fuel fumes are constantly being removed from the oil filler neck/crankcase when under vacuum.

There is one problem with my setup, in that you could cause too much vacuum in the crankcase (the closed circuit again), which might affect the seals over time, and that's why I added the Wagner M/E pcv valve, a two-stage fully adjustable pcv valve to limit the vacuum to about 8-10 in HG at idle. Just off boost it will be much higher due the two-stage pcv. This would significantly help relieve any boost pressure buildup before the engine returns to idle.

Mike

 

Likely to coat your engine bay with oil slick unless you have a very good filtration and cooling medium on a vented can. I'd much rather an exhaust spike to avoid coating the intake or engine bay.

 

Yeah, similar thoughts as Mike, looking forward to Active Scavenging with vent to engine(VTE) vs. Passive Scavenging with vent to atmosphere (VTA)

VTE vs. VTA debate reminds me of the synthetic vs. non-synthetic oil, or OMP vs. pre-mix, great stuff from both angles!

Briefly, i'm a fan of VTE, especially with the DCV-6 setup plumbed to both UIM & turbo inlet. My understanding, this setup keeps constant crankcase evacuation, lending to strong manifold vacuum during idle/cruise, and steady suction from the inlet under boost. Potentially, always “breathing out,” never letting pressure build.

VTA relies entirely on passive crankcase pressure to push gases out. It works, especially on cars that experience aggressive driving or track duty, *and* it fully isolates the intake tract ensures zero recirc of oil vapor. But for a street or dual-use setup, I like having the active vacuum to maintain stable crankcase pressure and consistent evacuation across all load conditions.

-Ed

 

Out of curiosity, where is everyone mounting there catch cans? Mine is mounted where the air pump used to be. I am not crazy about the location and want to move it. I have an HKS V mount.

 

I mounted my mini Mishimoto on the side of the silver-colored insulator covering the ABS on my LHD. Just drilled two small holes and bolted the bracket to it. It fit perfect with the hoses going behind the engine and along the firewall. Still have plenty of clearance to the UIM.
Mike

 

Finished install with the @ImprovedRacing DCV-06 and their CCS Catch Can.🎉 Also, finally installed the ReacTiV Fabrication titanium oil fill neck, needed the -10AN port for the vent.
Oh yeah, and the @JP3 Motorsports Catch Can mount is a perfect fit, super stable, and very easy to route the lines, I'd probably still be trying to figure out a mount solution, thanks JP3!!

A few pics first, scattered parts:


Oil Neck side by side:


Overview of DCV-06 placement, outlined in the green box. Coils are relocated and the emissions delete (simplified sequential?) performed to give a bit more room under UIM.




Overview of completed install all buttoned up.

 

Wow, thanks for calling out the M/E Wagner PCV valve, finished the install without it and quickly realized what you were alluding to; without a vacuum limiter, FD was hunting for an idle. I placed the OEM PCV between the DCV-06 and the UIM vacuum port (same place as you it looks like), and the idle hunting went away. Already have a tracking number in hand for the M/E Wagner Dual Flow valve w/inline adapter. Any tips, or pretty straight forward to tune it out? I do have a vacuum gauge as the manual suggests to assist.

Initial impressions...well the first night went for a ~75 minute drive, before adding the stock PCV -- mixture of boost, idling around, and street (to Harbor Freight, where else!? )

Took a peek and found:


Went for a 2nd drive the next day with stock PCV in place, took another peek after 60 minute drive, and the Catch Can, caught much less, barely anything. Yeah, the stock PCV appears to limit flow/vacuum very well -- it will be interesting to see the difference with M/E Wagner installed, like Mike mentioned, can tune vacuum based on either idle or cruise.

Another difference, without PCV, the oil fill cap is completely dry, looks good, no residue. After placing the PCV back, oil fill cap was no longer dry, but had a familiar residue on the roof of the inside cap.

Overall, fun experience, the JP3 Catch Can mount was key for the quick completion!
-Ed

edit, setup with M/E Wagner Dual Flow PCV now looks like:

M/E Wagner Dual Flow PCV placement

 

I use the small port on the M/E Wagner to attach your vacuum gauge. Run the engine at idle and adjust the first stage Allen set screw to have just a slight loss of vacuum as compared to completely off. I think I did around .25-.35 inHG or so of difference. This will allow some evacuation of the crankcase at idle but no significant vacuum loss or no significant negative pressure in the crankcase. Set the second stage to open just like the instructions that come with the valve say to set it. Works like a charm. IMHO, the best way to set up a catch can and still retain a PCV setup. Best of all worlds.
Mike