Crankcase vent vacuum setup removal = bad

[Ddan]

All well and good, but when tuners like BCM, Jon Nichols and MBP line up against removing the breather apparatus, you have an uphill issue of proof.

I started this thread with "prove it wrong."  Lots of opinions and no one's offered another tuner on par with BCM or the others who says otherwise.

I attended a couple of maintenance seminars at BCM.  Bruce did say that there was a theoretical gain to be had by increasing the vacuum in the crankcase, but he qualified it also by saying that you'd not notice the difference in our bikes.   

[Capo]

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.

Are you suggesting that the vacuum in the airbox is 1-2bar? This (2bar) equates to over six FEET of water or 200,000 pascals (incidentally bar is not typically used as a unit of measure for vacuum), if this was the case, what would the vacuum be below the throttle bodies?
also, a flow meter measures flow, a pressure gauge measures pressure, compound gauges measure vacuum and pressure, the preferred (and more accurate) instrument is a manometer.

The volume in the crankcase varies, as does the conditions for leakage past the rings.

The 'breather box' or 'reservoir' is actually a inertial separator that serves to reduce the velocity and cause a change in direction of the gas, this will remove most of any oil entrained within the gas stream, the removed oil collects in the bottom of the separator and drains back into the engine when conditions permit.

May I suggest that you run your tests again, only this time use the correct instrumentation, simultaneously measuring crankcase pressure, the pressure at the separator, the vacuum in the airbox and the vacuum below the throttle body, do this at 1000rpm increments from idle to max. This may give you the proof you seek.

[ducatiz]

Are you suggesting that the vacuum in the airbox is 1-2bar? This (2bar) equates to over six FEET of water or 200,000 pascals (incidentally bar is not typically used as a unit of measure for vacuum), if this was the case, what would the vacuum be below the throttle bodies?
also, a flow meter measures flow, a pressure gauge measures pressure, compound gauges measure vacuum and pressure, the preferred (and more accurate) instrument is a manometer.

The volume in the crankcase varies, as does the conditions for leakage past the rings.

The 'breather box' or 'reservoir' is actually a inertial separator that serves to reduce the velocity and cause a change in direction of the gas, this will remove most of any oil entrained within the gas stream, the removed oil collects in the bottom of the separator and drains back into the engine when conditions permit.

May I suggest that you run your tests again, only this time use the correct instrumentation, simultaneously measuring crankcase pressure, the pressure at the separator, the vacuum in the airbox and the vacuum below the throttle body, do this at 1000rpm increments from idle to max. This may give you the proof you seek.

1-2 mbar vacuum at the airbox and 2-3 bar pressure at the crankcase at 4500 rpm.  Manometer on the airbox and flow meter on the crankcase.  Was typing while multitasking.

[Bill in OKC]

On Mine I have the STM Crank case breather with the reed valve.
The reed valve makes a little flapping noise in there but it definietly lets pressure out.
I removed the intermediate breather box under the tail and routed some clear plastic hose directly to the airbox, via under the tank.
It cleans things up some and I know where the vapors go.

The flapping noise is the valve snapping shut when the pistons rise on the exhaust and compression strokes.  It creates a kind of a ?pre-evacuation? or temporary vacuum on the compression and exhaust strokes to get ready for the next intake/power/blowby stroke.  It is a really ingenious little performance trick.  Most meters that I am familiar with will give you an average reading - not the instantaneous readings that would be needed to see the difference in crankcase pressure between a power stroke and a compression stroke - a reed valve is very sensitive to these changes.

[MendoDave]

Now on the compression & exhaust stokes the other piston is in the middle of doing something else. Is it 90 degrees different on the 2v engines? or 180?

[mitt]

Now on the compression & exhaust stokes the other piston is in the middle of doing something else. Is it 90 degrees different on the 2v engines? or 180?

90 degrees - common pin.

when the vertical cylinder piston is at TDC (zero veloicty), then the horizontal cylinder is close to its maximum velocity (half way between TDC and BDC).

mitt

[MendoDave]

So if one Piston is making vaccum on the compression stroke then the other one is starting to make pressure...










(I could sure use spell check)

[RB]

So if one Piston is making vaccum on the compression stroke then the other one is starting to make pressure...

Correct,  Ducati V-twins fire every 450°. (this is easier thought of in terms of 180°, while one cylinder fires, the other is compressing the exhaust stroke.)
i can't say that i have the experience of BCM or Nichols and wish i could comment on the positive/negative affect of the breather debate. I find this thread fasinating.

RB

[erik822]

"Crankcase vent vacuum setup removal = bad" because it makes my head hurt.

[TAftonomos]

If you can vent the crankcase, contain any oil that is spewed out, and have it drain back into the case, that would be the simplest solution.  You could get fancier and add a vac bung to the exhaust and actually use the exhaust to pull a vac on the crankcase.  We used to do this all the time on high-po import motors (2.1l's spinning to 12k rpm and making over 270whp) and it was worth about 12 hp off the top of my head.  Potential problems include backfires into the case/block (eliminated with a check valve) and sucking oil out of the case/block (obviously bad). 

The stock system on the 999 has a large breather box to increase the volume and also to keep (or attempt to) oil from finding it's way up the vac hose into the airbox.  Never has on my bike, but I've heard/seen it happen to others.  Simple setup I've used many times on auto's is to fab up a catch can, vent the case/block to the can, and a hose goes from the can to a vac source before the TB (airbox).  Fill the can with steel wool to trap/keep any vapors.  We'd actually tap the block and run another line from the bottom of the catch can back into the block to allow another vent/oil drain path.  Now it auto-drains and it almost maintenance free.

Like BCM, without some testing I'd be suprised to see if a constant vac system would be a benefit to our motors.  Might make a horse or 3, but if it did you'ld see it used in WSBK.  Probably the benefits (a pony or 3) arn't large enough to outweight the drawbacks (more complication...and most importantly...weight).

Hows that for a first post?

Thank god there is alternative to VS now

[ducatiz]

Hows that for a first post?

Thank god there is alternative to VS now

Excellent 

[TAftonomos]

One thing I didn't remember to put is the reason you don't want oil/oil vapor in the airbox.  On a normalcompression bike or stock one, it shouldn't/won't matter.  Raise the compression and you might see a difference in the amount of timing you can/can't run.

Explanation - Oil vapor LOWERS the octane rating of the gas you buy.  It will cause the mixture to burn faster (lower octane), possibly causing pinging/detonation.  To counter this, less timing will be run, potentially robbing the midrange of some power and the "snap throttle" drive ability all twin guys like.  Soggy would be a better way to describe it.

All of the above will also be affected by combustion chamber shape, piston shape, squish area, and the like.  Until its a built motor and it pings, you should be fine with the stock system.  Another trick I've seen is mounting a corsa reed valve in the airbox, removing the reed in the breather assembly, and running the hose in that way.  Lots of ways to skin a cat that may or may not need skinning if you catch my drift.

I'm out....off to ride a s2 and a s4 and see which one I like better

[printman]

Been reading this, because:

A: The hose between my canistor/seperator box (under the seat) broke off. So I plugged it and have an open hole at the canister now, filled with a filament material from work.

B: Have thought about going to the K&N assy mounted up high, but was talked out of it by a reliable source.

Currently using the STM breather assy, does it offer or change my options?




A side note: If your bike (not mine) has a forced air induction. Does that not pressurize the airbox? And if the airbox is pressurized, how would the hose assy for the crankcase pull vacuum unless it is located where a venturi effect could take place? Confused on that one. More of a gearhead, than being able to understand the airflow aspects of it. 

[ducatiz]

Been reading this, because:

A: The hose between my canistor/seperator box (under the seat) broke off. So I plugged it and have an open hole at the canister now, filled with a filament material from work.

B: Have thought about going to the K&N assy mounted up high, but was talked out of it by a reliable source.

Currently using the STM breather assy, does it offer or change my options?

No, the STM breather is just a high-quality, bling version of stock.  Same reed setup and better sealing at the base.

A side note: If your bike (not mine) has a forced air induction. Does that not pressurize the airbox? And if the airbox is pressurized, how would the hose assy for the crankcase pull vacuum unless it is located where a venturi effect could take place? Confused on that one. More of a gearhead, than being able to understand the airflow aspects of it. 

Depends on the type of system, but generally you would have a compltely different setup.

[TAftonomos]

A side note: If your bike (not mine) has a forced air induction. Does that not pressurize the airbox? And if the airbox is pressurized, how would the hose assy for the crankcase pull vacuum unless it is located where a venturi effect could take place? Confused on that one. More of a gearhead, than being able to understand the airflow aspects of it. 

You would then take vac from the turbo inlet, as you stated correctly that the airbox would be pressurized.