Replace the filter on your catch can with a hose going to the check valve/slash tube in the exhaust. It needs to be sealed in order to pull a vacuum on your crank case.

I have both the stock ports in the valve cover plus a vent port in the side of the block going to my baffled catch can.

I also have a drain back from the catch can that goes to the very bottom of the sump below the oil level. I think Id rather change my oil more often to keep contaminants from building up than worry about draining the catch can all the time. The water and fuel in the oil should be more volatile so I’m hoping much of it gets sucked out as vapor leaving mostly condensed oil behind.

Bob

Agree on the dubiousness of the claim that an additional few psi of pressure differential between the top and bottom of the pistons on top of the compression and power stroke pressure would make much of a difference.

Having said that, even if the crankcase absolute pressure were dropped by say 2 psi (in the case of the slash cut on the Honda), that's about a 15% reduction and a 15% reduction in internal aero drag which may be what, <2% of the total output?

OK that makes sense. So what about this:

valve cover to catch can
catch can drain to sump
catch can also vents to slash and check valve

Yea, thats true! The magnitude is just off here. I can see a few horsepower, not 50 though. If that much energy was going into turbulence/heat or blow by your oil would be on fire :X

I think it would be worth maybe 5, if the suction was very good!

I was off on my numbers I think 16 hp out of 270. ~6% increase in power my friend recorded on his civic. It made a measurable difference in power.

Bob

Even if the gains are as little as a few hp it still sounds worth it. My biggest concern is interference and possible damage to the WB downstream.

Did he do 2 consecutive pulls with and without the suction connected?

This is true I could care less about a few HP. I’m just looking for a setup that doesn’t put oil back through the intake into the cylinders, I don’t have to worry about the catch can filling up and spewing everywhere, and also not be concerned that I might turn all my engine oil into mocha cappuccino causing engine wear.

I will be putting the fitting in the exhaust after the Wide band so I’m not worried about that.

Bob

I do not know.

Bob

post pics when you get it done!

My understanding of PCV is not very good, but I'm close to Bob in that I'm mostly interested in keeping oil vapors out of my intake tract, and out of my cylinders.
For my last setup, I did as many here seem to, put a breather filter on the cam cover, stock PCV in place. That kept my intake dry for over a year, but over time the filter saturated with oil, leaked, and otherwise put a nice film of oil in a lot of places in the bay.

On my current setup, I'm thinking of doing something different - run a hose from the valve cover breather to one port of a catch can, and put a breather on the other port of the can. Thought being it would trap the vapors in the can and stop the breather clogging. If anyone thinks that's dumb, let me know. This being mturbo I don't really need to ask I guess.

This exhaust vacuum source seems like a cure for turbo oil drain/ring sealing under boost, I'd imagine there was no need for a pcv at that point?

Unfortunately I'd rather not run without a cat. The air pump idea would solve that, but cost, weight, packaging, and complexity make that less appealing.

Place the slashcut post-cat.

Will you get a solid vacuum that far downstream?

doesn't look like that works per cupcar.

If this were doable then installing this is a no brainer for me. But as m2 said it needs to be further upstream to generate good vac. Since I'm running no cat I'd like to have it at least behind my sensor. Anyone think I'd get good enough vac behind my sensor?

Split's old DP which I'm using:

http://sphotos.ak.fbcdn.net/hphotos-...5_840639_n.jpg

Yes you will get fucking good vac there, shesssh,

if you are worried about the crude getting on the cat put a catch can between the Valve cover and the exhaust pipe to catch the crude buildup

The whole point of the catch can system was to keep the crude from being pushed back into the intake system imo, normally manufactures use the engines own vacuum to pull vacuum in the crankcase and for emission reasons to reburn the crap that comes out of the crankcase.

What I don't get is why people put on a catch can, vent to atmo, why not help the engine breath easier as well, put a vacuum into the crankcase, worried about oil going though exhaust? put the catch can on it than, thats why people used

Pulling a vacuum has been going on for few decades now, various ways to do it as well, exhaust, vacuum pump ( elec \ belt ), engine itself, etc

once my miata is running again ( timing belt ) I will grab a video with a boost ( vacuum+pressure) gauge attached to the line and drive it about tad showing it.

My catch can system.

-8 lines to the valve cover vents. Holes have been enlarged in the baffles in the valve cover.

Exhaust side valve cover vent goes into a small manifold that tees into a -10 line going to a port put in the block venting the lower crank case before going to the catch can.

-8 line going from PCV port to catch can.

Catch can is baffled with and a pot scrubber is used. Blow-by has to go down through the pot scrubbers then back up the central tube to get out.

-10 line return drain goes to very bottom of the oil pan.

The filter breather will be replaced with a -10 line going to a check valve and slash tube in the exhaust pulling a slight vacuum on the system.

Bob

Do you have a picture of said port?

Correction: FWIW here's my 1/4 NPT port, for 1/2" hose. Ignore the black hose, it's not part of the system.

https://www.miataturbo.net/attachmen...1&d=1294676439

I enlarged the tiny internal blowby hole. Described here
https://www.miataturbo.net/engine-performance-56/cam-cover-blowby-flow-crankcase-pressure-tiny-hole-modification-54742/

That must be 1/4" NPT. 1/2" NPT is much bigger on the threads. I had issues getting a 90 degree pipe thread to work getting it oriented right when it was tight half the time would crack the valve cover if you weren’t real careful because the wall around the threads gets thin.

Bob