| The oil vapors from the sump are piped back to the air intake to be burned instead of being vented to the atmosphere as air polution. So it's illegal to run the device you're talking about.
The theory for the best crankcase ventilation says that you loose less horsepower through pumping losses if you vent to a large volume. That's why the aftermarket setups initially looks attractive. But if you vent to an airbox vacuum, there are fewer losses than if you vent to a larger volume at atmospheric pressure. This stock system has the added benefit of a collection/separation tank between the crankcase and the airbox.
The following is a post by BCM Ducati, a top Ducati tuner here in the States:
What is different about Ducati streetbike breathers in general is that the reed valve is mounted directly in the case. The breather box location and volume are good.
The reed valve location is good for emissions but not for engine power and crankcase breathing. What happens is that under certain conditions, under high rpm and light load, the oil doesn't run back because of the reed valve and it builds up in the tube above the reed.
The simplest solution is to hollow out the reed assembly and leave it internally open but still hitched to the volume bottle. This allows the volume of the breather bottle to perform its function and usually gives a slight horsepower increase also.
Then, use either a 748RS reed valve in the airbox at the end of the breather hose, OR, use a Ford diverter valve (in-line one way) just before the airbox.
Never use an external atmosphere vented breather. It's a horsepower loss and you're asking for trouble as even the little filters don't stop the dirt from getting back into your engine.
Removing the volume bottle hurts peak horsepower slightly and doesn't allow a place for the air and oil to separate so that the oil can run back into your engine.
Run the oil level smack in the middle of the sight glass and never any higher. If you look at most superbikes, no matter what manufacturer, their crankcase ventilation systems are similar to what I've described. Even the Ducati Corse bikes are setup this way, only the street bikes which have to meet strict emissions requirements, are setup the other way.
We have successfully run this setup on Ducatis up to 1100cc with no issues.
[Edited on 11-27-2004 by Shazaam!]  | 
Shazaam!
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