Crankcase vent vacuum setup removal = bad

[truckinduc]

I like reviving old debate threads.

I am planning on building an aluminum catch can of sorts for my breather. Most likely it will be around 1-1.5 quatrs.  I cant remember how big the stock setup is.

[JimE]

Interesting thread.

I think the crankcase reed valve is a good idea. At some point the case must experience both a positive pressure and a vacuum. Hence the need for a reed valve. I think I'll trust the designers on this and leave that be.

My only guess for the pass through box by the shock is to reduce the pulsations that may be created under positive crankcase pressure to the airbox. Possibly to cool the oil vapor and drain some back to the sump but not likely. It's behind the motor and not very cool. If this were the case it would be up front. I can think of no better way to reduce pulsations to the airbox than to not have it go there at all. The atmosphere around me would be fine.

Having the crankcase oil vapor go to the airbox is a neat way to make sure an otherwise possibly messy situation stays clean. Also to satisfy smog. A good filter with proper maintenance should take care of this nicely (the mess that is, screw the smog stuff).

I'm not reclaiming any oil or anything by having it go to the airbox. That gets burned. So I'm taking oil vapor and mixing it in with my fresh air, thereby richening the mixture, but not in a good way. The oil is hard to burn, doesn't flash well. Flame propogation sucks. Little droplets get trapped at the edges of the combustion area causing dead spots. Worse yet, they interfere with the fuel burning. So I think if I plug that hole in the box I'm going to lean it out. It'll probably be minor and can be corrected with a jetting adjustment, which I'll do when I put the FCR 41's on there.

So at the end of the day I think I'll wind up with the aftermarket reed valve and a K&N on a bracket where the current little box by the shock is.

Interesting thread though. Lots of opinions on this topic.

[ducatiz]

I'm not reclaiming any oil or anything by having it go to the airbox. That gets burned. So I'm taking oil vapor and mixing it in with my fresh air, thereby richening the mixture, but not in a good way. The oil is hard to burn, doesn't flash well. Flame propogation sucks. Little droplets get trapped at the edges of the combustion area causing dead spots. Worse yet, they interfere with the fuel burning. So I think if I plug that hole in the box I'm going to lean it out. It'll probably be minor and can be corrected with a jetting adjustment, which I'll do when I put the FCR 41's on there.

So at the end of the day I think I'll wind up with the aftermarket reed valve and a K&N on a bracket where the current little box by the shock is.

Interesting thread though. Lots of opinions on this topic.

yes, lots of opinions.. all the builders who don't sell a kit to remove it are saying leave it on, whereas the guys who sell a kit are saying to remove it!  Having BCM, et al, say it is better to leave it on pretty much does it for me.  they don't get anything for offering that opinion.  if they wanted to make a kit and sell it, you can bet ppl would line up for it if they recommended it.

the amount of oil vapor that ends up in the airbox is nil or practically nil.  check it for yourself.  the way the stock system is set up, the oil vapor cools and liquifies before it reaches the airbox (which is why there are multiple chambers in the system).  airbox provides vacuum, pulls the crank air.  oil vapor travels up the tube and begins too cool immediately, by the time the air reaches the second chamber of the first breather box (look under the seat, it is bifurcated), all the oil has pretty much liquified and stays there.  if you remove that hose, the oil droplets will come out. 

when the reed is under pressure (i.e. case pressure or vacuum) , the outside expands and prevents liquid from reentering, but when the engine is off and there is no moving air, the outside relaxes and the oil can reenter.. pretty neat setup.

[Howie]

Your Duc engine always has positive pressure.  This is due to piston size as compared to  crankcase volume.  This is why you have a one way valve out and no way for air to enter your crankcase like you do on your car.  The breather box is a rather large area with some negative pressure to help relieve crankcase pressure and store the vapors until they can be burned by the engine.  Removal of this box makes your system a little less efficient.  The only reason to remove this box, IMO, is to allow other modifications.

[battlecry]

I looked at the breather box a while back and didn't like the location or size.  I also didn't like the hose constriction, as the crankcase flow starts on a .75" hose and gets to the airbox on a smaller hose.  Actually built a fiberglass breather box to fit on the area under the cowling but the two .75" hoses made the thing ungainly. 

Ended up with a Nichols breather and a .75" hose going to the rear and a second one way valve on the hose by the beer tray, with the hose venting at the rear.  The reed valve in the breather is not a full one way valve, as it must let the condensed or expelled oil back into the crankcase.  On my bike some of the oil vapor/mist collects on the hose and drains back into the crankcase through the Nichols breather.  The second one way valve at the rear handles mostly vented gas.  I wish there was more air volume capacity on the hose but like all else on my bike, it is a compromise.  The location on the original breather box was replaced by a better voltage regulator mount.     

[scott_araujo]

I'd like to remount my regulator for better cooling but don't want a Nichols or similar with the breather filter element.  Maybe routing the hose a little further as mentioned above is an option.  I'll have to take a look and consider that.  I think the only reason the stock breather box is so big is to fit a little maze inside.  Fumes escape to the air box but liquid oil droplets hit a vane of some sort and drip back to the case.

Scott

[Langanobob]

I am not sure how much vaccum the ducati airbox can create to help evacuate the crankcase...

I think the hose is routed up to the box foremost as an EPA dump for oil blown out the crank, then it is burned instead of dumped on the ground.

mitt

Reply from Shyster:

based on my flowmeter, about 1-2 bar.  the connection is below the filter so it actually gets "preference"  combine that with the 2-3 bar pressure from the crankcase and it does what you say.

most of what gets sucked in is combustion gases and gasoline fume, only a little oil since the reservoir condenses the oil and it drips back in.

Shyster, this is a good thread and I'm glad it got revived.  In re-reading it I think it's time for some definitions and basic physics, especially since you corrected someone else for misusing the term 'blowby'.  First, flowmeters measure flow, either mass or volume flow, as in pounds per hour or say liters per minute.  Pressure gauges measure pressure as in psig or psia.  If you actually had a pressure gauge rather than a flowmeter hooked up to your airbox and measured 1-2 bar of vacuum something is wrong.  A bar is about 14.5 psi and a perfect vacuum at sea level is about 14.7 psi.  No way to get to 2 bar of vacuum or even measurably above one bar and specialized vacuum pumps take a long time to pump even a small sealed container down to near to absolute vacuum.   My point is not necessarily to be critical, just to point out that if you are to challenge others to prove you wrong, you at least need to get your ducks in a row with basic terms and numbers correct. 

[ducatiz]

Reply from Shyster:

i didn't do it myself -- well, all alone that is.  i'll see if i can get Todd to come on here and explain it or at least post his actual method and measurements he got off my bike (a '95 900SP with lots of mods).  i helped.  ran it up on the dyno, and sat on the bike while he hooked it all up and spun it up myself.  it was actually his idea because we had been talking about blowby and the effects of positive crank ventilation.  we are both engineering nerds, except that i went into law after college and he stayed in engineering.   tune in again later...

[TAftonomos]

Saw this, and might have some pictures to add in the next week or so.  I'm making a new breather box out of composite to fit under the solo DP seat.  I will use a corsa reed valve mounted in the airbox, and a billet breather where the stock one goes with the reeds removed.  This will allow oil to drain back out of the catch can much easier, and allow a larger breather box to be used.  The stock breather box won't really work with my new subframe, which is why I ended up needing to fab a new one.

[JimE]

Thinking of this, I just did it. Got a nice little stainless filter for the end of the breather hose, used a plastic radiator drain plug at the airbox hose fitting, then fabbed a little bracket to support the filter, attached it to the end of the hose, attached the bracket to the forward bolt hole from the old box, and safety wired the filter to it.

Works like a charm. About 500 miles and nary a drop of oil out of it. Np performance difference I can tell. My bike does a lot of starting and stopping and lot of around town with bursts of freeway and twisties in between. I'm on the throttle a lot and starting from cold a lot. Cost about $18 in parts with my account.

So I dunno what you guys are talking about. Works fine for me.

Cheers,
Jim

[ducatiz]

So I dunno what you guys are talking about. Works fine for me.

Cheers,
Jim

Sure, and a car will run fine with water in the crankcase for a while... 

Volvo Cash for Clunkers Engine Disabling

[ducpainter]

That's a clunker?

[ducatiz]

That's a clunker?

<OT>

YEP.

Plenty of vids on youtube showing awesome looking cars being trashed.

[Langanobob]

i'll see if i can get Todd to come on here and explain it or at least post his actual method and measurements he got off my bike (a '95 900SP with lots of mods).

Thinking about it later, I probably got confused over the term "bar" which is a well defined engineering pressure unit.  He may have meant the scribed lines or "bars" on the scale on a manometer or something else.   Hope I didn't sound critical, sometimes there's a thin line between confused and critical. 

[pennyrobber]

This thread surfacing again got me thinking. The pic below shows traces of the vertical cylinder in blue, horizontal in green and combined volume in red (based on 992cc). S is spark, C is compression stroke, P is power stroke, E is exhast stroke and I is intake stroke. The combined volume basically indicates the approximate volume (con-rods and so forth not considered) in the cyclinders on the crankcase side during an engine cycle (duc motor). You can see that the total volume under the pistons fluxuates by about 650cc. One thing to note is that the intake strokes take place mostly during the period when crankcase volume is being decrease by piston motion. This would suggest that connecting the crank breather to the airbox would lead to the assistance, by intake "suction", in evacuating the pressurized crankcase gas created by decreasing the volume of the crankcase.