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Tue Apr 08, 2014 6:19 pm

Anybody have any advice or know of any articles that describe the correct way to vent the crankcase? I have a 2332cc I am building and want to make sure this is right. Thanks to all and hope all is well.

Tue Apr 08, 2014 6:24 pm

Start with valve covers. If there's a problem add a case vent.

Tue Apr 08, 2014 7:13 pm

This is going to open up a can of worms.

My experience: I've never needed valve cover vents. On small CC engines (1915 and down) I vent through the fuel pump location and use the stock oil filler vent with the road draft tube. On larger CC engines, I've had issues with the valve cover vents and oil filling the breather box. I added a third vent to the case and the problems went away.

The way I see it, the case pressure is localized first in the case, so why not vent at the source?

Tue Apr 08, 2014 7:41 pm

bugguy1967 wrote: This is going to open up a can of worms.

My experience: I've never needed valve cover vents. On small CC engines (1915 and down) I vent through the fuel pump location and use the stock oil filler vent with the road draft tube. On larger CC engines, I've had issues with the valve cover vents and oil filling the breather box. I added a third vent to the case and the problems went away.

The way I see it, the case pressure is localized first in the case, so why not vent at the source?

Bingo, couldn't agree more.

I run a big 3/4" breather off the alternator stand on my race motors and eliminated all of my valve cover vents entirely. ALL of my oil blowby issues went away when I did that.

Crankcase pressure doesn't start in the valve covers, so why vent there first? Vent the source. The case.

Tue Apr 08, 2014 8:01 pm

I believe I've asked before, but could you please send me a link to that valve you have on your header to connect to an oil can?

I'm guessing the box has to be sealed and you need a sand seal as well, correct?

Tue Apr 08, 2014 8:03 pm

Is there such a thing as too much venting?

Tue Apr 08, 2014 8:07 pm

Quote: Is there such a thing as too much venting?

Good question!!!!

Tue Apr 08, 2014 8:15 pm

I don't think so as long as you're venting from the right areas. If the valve covers had a built-in baffle, I don't see why they couldn't be vented as well, but they typically don't.

A bit of vacuum actually works a lot better than just openings where the pressure can escape. Most would have a hard time NOT getting their rings to seal with an exhaust-driven vacuum source like Eaallred has, or had.

Edit: maybe even a baffle couldn't stop that tidalwave of oil coming in at high RPM. Add a drain for the oil to return to the sump, then a vent can be used properly.

Tue Apr 08, 2014 8:41 pm

Here's my 2 cents.

Crankcase fumes are corrosive to your engine's innards, so try to set up the crankcase ventilation so that it not only relieves crankcase pressure, but it also circulates, so that fresh air enters and fumes exit. You can use the stock entrance and exit (the unsealed pulley and the alternator stand) or make your own, pehaps putting a sand seal on the pulley and a filtered inlet on a valve cover.

IMO, if set up right there is no reason to vent fumes into the atmosphere. These fumes can be recirculated back into the intake to burn up any unburned fuel left in it. Plus the intake can help pull in these fumes and therefore help fresh air circulate inside the crankcase. This can be done with a PCV valve or just using the restriction caused be the air cleaner like stock, although most stock VW systems incorporated a flap on the air cleaner to provide the right amount of suction for proper circulation.

The crankcase is full of oil spray so it is likely that you will get oil in your crankcase "exhaust". Oil, of course, will increase the chances of detonation and foul the spark plugs. You can reduce oil spray by using a ventilation tower so that air flow slows down causing oil droplets to fall from suspention and collect in the bottom of the tower where the oil drains back into the crankcase. Again, you can use the stock alternator stand for this or make your own. Or just vent to the atmosphere.

It has been noted that the left valve cover tends to fill up with oil at high RPM, and venting this cover may make things worse. However, there may be ways to stop this problem and still vent the left valve cover.

I haven't heard of anyone doing this on a VW engine, but some hotrodders put a vacuum pump on the crankcase. This lowers the aerodynamic drag caused by the crank and rods and keeps the rings seated. The downside is that you lose some oiling advantages caused by swirling air in non vacuum crankcases meaning you may have to put oil spayers on everything not pressure fed.

http://www.vw-resource.com/air_cleaner.html#crankcase

Tue Apr 08, 2014 9:23 pm

There are plenty of vacuum pumps on VW engines; just not on street engines. I hear they pull oil away from the valve cover area in some sort of negative way and aren't suitable for street use. It seems to me that by slowing the pump down enough by swapping pulleys could work for the street.

Tue Apr 08, 2014 9:27 pm

Well that is a pretty far-out theory... I would add a pine tree air freshener to the crankcase air inlet. :wink:

Tue Apr 08, 2014 10:12 pm

You can't vent a case to much. But you can pull to much vacuum on an engine and starve the rings and wrist pins of oil. A typical vacuum pump system has a relief valve to limit the amount of vacuum.

I run a vacuum pump on the street car, limited to 12" vacuum. A couple solenoids control the system to make the system act like a regular breather and drain the catch tank below a set rpm and throttle position.

The rail runs a typical crank case evac system since space is limited.

I tried a pair of 3/4" drain lines to the sump from the valve cover which didn't do a lot to fix the oil issues i was having at the track. Eliminating the valve cover vents and venting the case did.

As of 5-6 years ago you will never see a valve cover vents on any vw of mine.

Tue Apr 08, 2014 10:56 pm

A guy could try an electric air pump and get circulation and a mild 3" hg of vacuum.
http://www.turbo-mopar.com/forums/showthread.php?27978-Electric-crankcase-evacuation-pump

I wouldn't draw off the valve covers, but I do believe if you hook up filtered intake air there it would be benificial as long as you have something pulling out the fumes elsewhere. But what do I know?

Wed Apr 09, 2014 3:24 am

I think the venting of valve covers is a "monkey see, monkey do" - guys have seen a return to valve covers and incorrectly assumed it was being vented from there. Unless you have really bad exhaust valve guides the valve covers should have negative pressure, as the main blowby is past the rings into the case.

Wed Apr 09, 2014 4:52 am

I have a different opinion. I feel the valve covers need to be vented so oil can return to the case much quicker. Where you install vents on the valve cover is important and looking in the picture gallery many people install vents in the wrong place. They need to be on the top at the front of the engine. On my 2276 that sees 7000 RPM I vent both valve covers, fuel pump location and oil filler tower. I use the cheap $30 Bugpack breather box and not a drop of oil comes out the top.

The left 3/4 valve cover Filling with oil can be reduced if you follow all the Bob Hoover HVX mods.

You should never vent to the air cleaners.

Wed Apr 09, 2014 4:59 am

Dave. As long as you go in a straight line that works. if the same set up was to be used on an engine that takes high G impacts it would fill the breather in no time flat.

I concur with the crank case breathing. The pressure in the valve cover area HELPS send oil back to the case faster than with vents on. IF one needs to vent the valve vovers for what ever reason, one of the tricks to make it work properly is to reduce the hose to 1/4" and then connect it to the center beather box.

T

Wed Apr 09, 2014 5:02 am

Type 5 Joe wrote: Well that is a pretty far-out theory... I would add a pine tree air freshener to the crankcase air inlet. :wink:

Best response ever on this hot topic, Lol!

Wed Apr 09, 2014 5:45 am

Venting a valve cover has no benefit to aiding in oil draining back down to the case. In fact it makes it worse.

With no venting at the cover, there is no air flow up the pushrod tubes so oil can drain back without resistance. With a vent in place you now have a path for air flow. Now crank case pressure is flowing up the tubes to the valve cover area. This adds resistance to oil flowing back down to the case as well as contributes to flowing more oil mist and windage up to the valve cover area.

Wed Apr 09, 2014 5:57 am

If your case is vented correctly there is no reason for valve cover vents .. my 1 cent

Wed Apr 09, 2014 7:42 am

Extra crank-case venting is really only required in circumstances of excessive blow-by due to worn rings or poor engine machining/assembly. If your rig is straight and rings sealing correctly, you should have little more blow-by than a stocker... so the stocko VW system is a simple and inexpensive place to start.

Some track/comp classes require a breather box... which is why I have one of the $20 Bugpack widgets on my 1916 comp donk.

Venting from the fuel pump location is not ideal as oil flung from the cam gear gets cast straight up the vent tube...or so I have been told. I have never experienced it as I have never a breather to that location

Hope this helps