crankcase ventilation

[digger]

Thanks for this. and appreciate the explanation. I am still learning about this level of engine detail, so forgive my ignorance - I may have misspoke. Now I understand that crankcase = slight positive pressure (can create blowby), valve cover vent = slight negative pressure (?).

The positive pressure is caused by the blowby entering the crankcase and not being able to escaping without significant resistance plus some action caused by the piston pumping action inside a "closed" system.

Venting the crankcase using the valvecover using appropriate mean will reduce the pressure buildup and can achieve negative/vacuum depending on the details how it is done.

I was told by the crew that tuned my car that a catch can will make the engine "run healthier" and eliminate the vapors. But they didn't go into detail about the installation.

Compared to simply venting to atmosphere adding the catch can that vents to atmosphere will not change how the engine runs but will reduce the mess as the majority of the liquids get captured and stored in the can and mostly gases escape from the catch can but they are not perfectly efficient.





You can also TIG/braze a nipple to the dipstick tube or splice in a steel tee instead of using AN but you want to maximise the bore sizes of the nipple and any hoses to match the separator size

[zaq123]

Thanks for this. and appreciate the explanation. I am still learning about this level of engine detail, so forgive my ignorance - I may have misspoke. Now I understand that crankcase = slight positive pressure (can create blowby), valve cover vent = slight negative pressure (?).

I was told by the crew that tuned my car that a catch can will make the engine "run healthier" and eliminate the vapors. But they didn't go into detail about the installation.

Right now, I have the valve cover with a filtered vent (see pic), but it constantly seeps oil and smells strongly of oil vapor. So my first course of action is to run that to a catch can and move the vent to the catch can (vent to atmosphere). I already bought the catch can so that should be an easy, temporary install. I do like what you did to close off that loop entirely and drain any blowby back into the crankcase.

I have no idea how much blowby i am getting, as i don't think there is any way to see evidence of that?

My goal is to allow my engine to "run healthier". Seeping oil and vapors is not acceptable long term. I think your setup is the cleanest. I can CAD model most things in Fusion360 and have access to all kinds of 3D printers and high-temp materials, so maybe there is a 3D printed solution.

M20 really had no good vacuum source for the crankcase by design, primitive PCV system. Bitch tube is just basically a crank case vent to the head /valve cover, similar to what's happening in the timing case in the chain driven engines. Valve cover vent is routed to the throttle body before the throttle plate. So like nothing that creates any significant vacuum in the crank case really.

You definitely want to something different there. If you gonna use a catch can, you'd need to add it to the maintenance items when you do your oil changes. Avoid long lines and aluminum cans. You want to keep those vapors as hot as they are when leaving the valve cover. Otherwise your catch can will be working as a condenser and creating all kinds of mess. So Id look into plastic catch can and place it somewhere where it's warm in the engine bay, close to the motor. If driving in cold climate, maybe even insulate it. Look into Provent by mann+hummel. Probably best catch cans out there.

The compression test is a quick way to see if your rings aren't sealing and creating excessive blow by

[zaq123]

You can also TIG/braze a nipple to the dipstick tube or splice in a steel tee instead of using AN but you want to maximise the bore sizes of the nipple and any hoses to match the separator size

that would be the easiest way indeed. I had no access to brazing equipment or TIG hence AN which was cheap.

[zaq123]

This is cool as hell. Stupid question, but do you think running just metric barb fittings would also be feasible instead of AN lines? I know AN has advantages, but I like keeping my car all metric and not needing the special wrenches, and do you think this would still work out and fit on the stock single-TB setup? I'm thinking I might be able to drill out a hole on a dipstick tube, have a guy I know weld a nut on there as I imagine it's too thin for tapping, screw in a threaded barb fitting to the nut, and run a hose that way up to a catch can.

Also, Tark, who made that neat little 2.8 plaque that mounts to where your intake was? That's a really slick detail.

Anything will work. AN is not needed there for what it was designed, there is no significant pressure there in the dipstick for AN to seal as it was designed to seal. I used AN because it was the easiest/cheapest way for me. Dipstick isn't like a maintenace item, I never plan to take that fitting apart ever again.

[zaq123]

zaq123 i am completely missing what you refer to as an “airbox”. do you mean a plenum?

yes plenum.

[digger]

can someone remind me if there an o-ring in the block where tube slides in? if so what is the size?

[hasa]

BMW

11151714390

27×2,8mm

[zaq123]

dipstick tube? No oring, slip fit. I use Curil K2 or T2 there to keep things sealed and not rusted/stuck together.

[digger]

BMW

11151714390

27×2,8mm

looks like the bitch tube o-rings not the dipstick

[zaq123]

no o-ring there