Crankcase vent vacuum setup removal = bad

[scduc]

This may be off topic, but I was sceptical after reading the first couple of pages on this topic ( even though I posted on page 9). I went ahead and did the whole plumbing removal and installed pod filters and the crankcase breather. I personally think the bike has never ran better. My only issue is when its cold, it revs low and I have to give the throttle a little blip at every stop. This is due to the stepper motor. I dont wheelie so I'm not expecting the oil spewing to the rear wheel. I really cant tell if there is power loss, but the weight savings and the clean look out-weights the possible -1hp. I ran my 750 with the crankcase breather fot 10k miles and never had oil come out of the filter. It also appears that many of you are looking to get the absolute most out of the engine as possible. That case I suppose the pressure boxes will play an important role. For the street, I really don't see it as a big deal.

[junior varsity]

While I "perceive" that mine runs well w/out the system, a goal for removing mine was the same as for removing the EGR system from my truck: only clean air is going in, no oily mist from the crankcase, nor bits of carbon build up from the exhaust emissions. If that comes w a slight adverse effect on performance, it is outweighed by cleanliness and related long-term performance/longevity. (mostly referring to the automobile EGR setup, but in a small way, I think the same is true for carbs + crankcase vacuum)

[koko64]

While I "perceive" that mine runs well w/out the system, a goal for removing mine was the same as for removing the EGR system from my truck: only clean air is going in, no oily mist from the crankcase, nor bits of carbon build up from the exhaust emissions. If that comes w a slight adverse effect on performance, it is outweighed by cleanliness and related long-term performance/longevity. (mostly referring to the automobile EGR setup, but in a small way, I think the same is true for carbs + crankcase vacuum)

During recent dyno tests I saw the EGA readings go up at idle by 0.4-0.5 leaner when the breather hose was detached from the air box (and blocked off of course). DP wasn't surprised by this and I suppose I shouldn't have been, but it bears out what you are saying. I had to richen things up with clean air going in! Just illustrates the effect of that oil mist on the A/F ratio. I agree it's better to keep things clean after seeing that.

[MonsterHPD]

Since this thread is so long, I have not read all of it, but I found the discussion at the beginning concerning crankcase vacuum (or not) quite interesting.
Many years ago (unfortunately …), I had a Yam XS650 / 860 twin (capacity increase by use of  bevel-900 SS pistons and liners, by the way) where I had some problems with the crankcase ventilation. In the end I had a setup consisting of  an approx 25 mm hose from the oil filler hole, in-line Ducati reed-valve stopping backflow into the engine as the (parallell)twin pistons rose together, potentially pumping 860 cc of air into the crankcases each revoulution, and an approx 20 mm hose leading into a catch bottle. This catch bottle was then vented to the atmosphere.
The hose leading into the bottle ended just above the bottom of the bottle, with the intention of keeping  inflow into the bottle as far away from the vent opening at the top as possible. After a few 100 km some oil would collect in the bottle, eventually submerging the end of the hose coming from the crankcase.

With this setup, I noted that after the engine was stopped, oil would slowly get sucked back up into the crankcase vent hose, rising maybe 20mm to 30 mm above the bottle oil level, and staying there quite long before sinking back.

My conclusion was that the venting was good enough to get any blowby as well as the 860cc geometrical compression in the crankcase on the piston downstroke out of the crankcase, and the reed-valve set-up was tight enough to allow the pistons to draw a slight vacuum in the cases on the upstroke, resulting in a sub-atmospheric pressure in the cases.

Of course, it's not below athmospheric all the time, if it were no oil would have ended up in the catch bottle, but it's my belief that  with a set-up like this, and possibly due to the parallell-twin layout, you can have crankcase pressures that are below athmospheric during part of the working cycle.
I suppose maybe the engine is most likely to stop with the pistons shortly before TDC on the upstroke, this beeing the most likely position to create a slight vacuum in the cases to suck oil back up the vent hose.

[koko64]

Building a motor like that is a good test bed for the theory. Very interesting.
Cheers.

[ducatiz]

start watching at 1:24

[koko64]

Do you think it is a small version of the vacuum pump used on drag racers, or at least similar in concept?

[ducatiz]

Do you think it is a small version of the vacuum pump used on drag racers, or at least similar in concept?

that's pretty much what he says.. i'll be interested to see it in the parts manual when its published --- God knows I can't buy a new bike right now lol

[koko64]

Spose those massively oversquare bores are allowing such high revs, pumping losses have become a real issue. No surprise as the bore to stroke ratio sets a record for a twin. 
I hope the gear cam drive makes it to the rest of the models.