Crankcase Vent Air Filters

[SoCalManche]

So I've seen a few guys on here throw on a mini air filter on their aluminum valve covers after doing that swap. Can someone give me a little more info on why you would install one? Which filters are you using?

[gogmorgo]

The way the crankcase vent system works is the one vent is attached plumbed to the intake manifold, behind the throttle, and the other end is plumbed to the intake ducting, pre-throttle but post-filter. The higher vacuum of the intake manifold draws out crankcase gasses, which then get replaced by clean air from the air filter.

If you’ve got an issue with the vent system, combustion gasses and oil vapour can get pushed back into the air box, gumming up the filter, throttle body, etc., and the condition is aggravated by excessive blow-by. Putting a filter directly on the valve cover separates it from the intake, but doesn’t address the problem with the vent system (or the blow-by).

 

On the other hand, if the vent system is working but you’ve installed an aftermarket air cleaner that doesn’t have a convenient location to attach the vent hose, you’ll want to find an alternative way to get a supply of clean, filtered air into the crankcase. Hence the filter on the valve cover.

 

Pressure needs to be vented from the crankcase. It can be left essentially open, any attachment to the intake blocked off, although the oil vapour will make a mess in the engine bay. A catch can addresses that issue, but will need periodically emptied. Depending on your local emissions regulations, it may also be difficult to pass if you choose that route. Burning combustion waste gasses and oil vapours in the engine is better than releasing them straight to atmosphere.
But you do need some form of crankcase vent. There will always be some amount of blowby even on the newest engine, not to mention pressure changes in the crankcase due to changing temperatures, and if you don’t allow it a path to vent, it will find its own. It’s also not good to introduce unfiltered air to the crankcase, and it will always get pulled in from outside as the engine cools. 

[Pete M]

my little filter kept getting soaked in oil.    just something to keep an eye out for.

[ghetdjc320]

I also work a lot on jet skis and we use a small catch can with a tiny air filter on it. Those are only on supercharged skis though. In a stock or even stroker 4.0 I’d  just reconnect the vent system back to factory specs. It works well that way. Just make sure the baffles in your valve cover don’t get plugged up with junk. 

[gogmorgo]

Cruiser54.com

There’s a tip about valve cover baffles. 

[SoCalManche]

Yeah, I already did the valve cover mod for the baffles. I was just curious as to if the air filter on the valve cover itself had any real upside/downside. My system is setup in factory style. Thanks for the info!

[jubalb]

I was just randomly reading through some threads.  Years ago I had a real bad blow bye/blowback problem with my Comanche 4.0.  Oil was going straight into the air filter housing.  So I made a catch for it, I had to check it often.  After redoing the head and a lot of work to the truck blowback basically stopped.  Then I ended up putting a little air filter coming off the valve cover.  You can pick them up at any auto parts store.

[Pete M]

7 hours ago, jubalb said:

I was just randomly reading through some threads.  Years ago I had a real bad blow bye/blowback problem with my Comanche 4.0.  Oil was going straight into the air filter housing.  So I made a catch for it, I had to check it often.  After redoing the head and a lot of work to the truck blowback basically stopped.  Then I ended up putting a little air filter coming off the valve cover.  You can pick them up at any auto parts store.

 

I had a little filter for a while and I can say for certain that it's important to fix that blowby first like you did.    I just saturated the filter in like a week and leaked oil all over.