Crankcase vent vacuum setup removal = bad

[koko64]

I suppose it's all a balance between competing tuning principles.

Keeping the intake charge clean Vs vacuum assist to crankcase breathing.
Strong air box vacuum Vs open air box and maximum air flow.
Resonance mangement Vs Strong air box vacuum.
Creating crankcase volume Vs constraints with space.
Crankcase venting and pumping losses Vs emissions and noise laws (if you care).
Etc, etc.

Given the constraints of the long manifold carb motor and it's compromised air box, the above issues have to be dealt with in terms of their tuning potential.

The testing I am doing is to prioritise the tuning effort.
Any advice that could save me dyno time$$ is welcome.

[koko64]

i've always understood those boxes were meant to catch oil.  sort of a centrifugal nautilus design..  like the old VW oil bath air filters -- the oil never gets sucked into the vacuum because it has to go past several right angles, against gravity. 

Very true, but they are also cavities that provide for virtual crankcase volume increases. This includes things like the Corsa breather box, the air box and oil seperators. They all add up to increased crankcase volume. What I have trouble understanding is if you can get away without vacuum assistance then why not vent to the atmosphere? I know some racing regulations stipulate enclosed breathing systems for safety in case of of an oil puke (like EPA), but some race tuners vent to the atmosphere but with an oil catch bottle.

Maybe it's the V-twin's pumping losses compared to the inline four, apples and oranges.

[Bill in OKC]

Isn't that the race set up that has been mentioned?

I mean with no reed valve venting into a huge breather/oil seperator box and then back to the air box via a auto type one way valve? The breather box gives the extra volume and often sits in the tail section.

That link explained it well, the Corsa set up.

The race setup does have a remote reed valve when the full system is used.  I have seen a few use the race breather without the remote reed, not the complete system, which I suspect reduces power.

[koko64]

Thanks guys for going over this with me after the mother of all threads.I appreciate the responses.

I have only seen pictures of the Corsa system, I've only eyeballed in line four race set ups. That would be cool to run on anything big bore or racing I reckon. Could probably run it on a Superlight. I'll probably rig something up near the steering head under the pods on the Monster if I don't get lazy and slap a mini K&N on the oil seperator box.

Just couldn't find a loss on the dyno with the breather hose detached from the air box with the stock set up. Wasn't racing though or holding it flat out for too long, just enough for the EGA to clear the accelerator pump.

Just 'guestimating'; little filter on the breather probably a power loss and oil leak/crash risk, seperator box to atmosphere or air box not much difference. I'm saying that the Monster system is a very poor man's copy of the Corsa system and don't do much due to constraints on packaging. Small oil seperator box, whimpy air box, reed valve for emissions more than power. It's beter than nothing and keeps the EPA happy though.

Does that ring true to you?
(Kind of thing to discuss over a few beers, but I'm across the Pacific).

[Raux]

I've read about 50% of the pages.

For the system with the tube going into the airbox, especially a pressurized airbox, I think it would not help the system and may even hurt at speed. No test on a Dyno would show this.
If the crankcase is pushing 3 bar and the airbox is pressurized say to 4 bar, there would be no venting and in fact it would stop venting thereby increasing pressure in the crankcase.

the old TT bikes had a box under the seat with the crankcase venting to that where the oil and air were separated and then vented to the air. which would allow the positive pressure of the crankcase to self regulate.

I would suspect even with the stock Monster airboxes there is some pressurization going on at speed to keep up wiht the increased demand of the motor at higher RPM. again no way for test equipment on a dyno to show this.

[koko64]

Thanks Raux, food for thought.
The system you described is what I will try with the pods. Adding further volume  is something I will consider with an extra breather cavity. I will try to use the largest filter I can fit off the oil seperator, to minimise any restriction.

Air box resonance or pressurization affecting crankcase breathing is something I want to avoid. I suppose thats unlikely with pods.

I like the idea of keeping the intake charge pure.

[Bill in OKC]

I'm saying that the Monster system is a very poor man's copy of the Corsa system and don't do much due to constraints on packaging. Small oil seperator box, whimpy air box, reed valve for emissions more than power. It's beter than nothing and keeps the EPA happy though.

Does that ring true to you?
(Kind of thing to discuss over a few beers, but I'm across the Pacific).

I agree that the system is a poor-copy of the Corse system, but you have it a little twisted.  The reed valve is in the Corse setup - doesn't that mean it is more for power than emissions?  The hose to the airbox is not on the Corse system - and you have proven it does not change horsepower - that kind of indicates it is an emissions thing for a Duc motor.  A dyno without the reeds would tell the tale.

[junior varsity]

The Corsa system goes like:

From Crankcase to Box:
    Crankase 'breather' (no valve) - hose - underseat breather box.

From Box to Airbox:
     Underseat breather box - hose - airbox.... with valve...

[koko64]

That's what I understood j v.

Just been looking at Ian Falloon's desmoquatro book and you can see the hoses to the breather box and back to the air box on the '93 888 Corsa.  On the 888 and 996 Corsa bikes you can see just how substantial the breather boxes are. A lot of volume there.

Also been looking at Neil Spaldings book Moto GP Technology, a picture of the WCM bike shows a hose going to breather cavity (cylindrical tank) in the tail, but a hose out the back of the cavity to the big wide world!

[junior varsity]

Yep, that's the setup on the 748RS and the rest. The size of the undertail breather box varied with the subframe/computer model and whether it was a race-only model (RS) or a street version with DP setup.  The difference, as I understand it, is achieved from moving the valve to after the breather box, by the airbox, thereby increasing the available crankcase volume itself.  The crankcase volume is not increased by anything after the valve, so on the stock setup with the valve inside the crankcase breather, there's no additional volume gained from the breather box, it serves only as an oil collector tank where the oil can then slowly drain back into the motor at the crankcase breather.

[koko64]

Thanks j v.
That is illuminating indeed and settles things in my mind. The most important information so far..
The valve location changes everything. It of course explains the valve location on the race bikes.

I take it's therefore only worth adding extra cavity volume if I'm going to move the valve to the end of the system.
I can remove the reed valve and bung a race type valve in a hose after the seperator box? That effectively adds crankcase volume without adding an extra cavity by shuffling the order of components. It utilizes the existing cavity.

After seeing the WCM system I'm feeling better about not venting to the air box. Real old school. The real reason they got disqualified !

Cheers

[junior varsity]

Post a picture of that one if you can.


if you were going to fab up your own - using the existing two front tabs where the fusebox attaches, and the aft two holes by the tail light / seat latch, you'd want to go "in" at the bottom of your box closest to the engine, and 'out' (to the airbox or otherwise) at the aft section, at the 'face'. 

Here's the "BIG" volume underseat breather box for the 748-916-996-998:



And what I am trying to describe in action on an 888 Corse:




















And there's always the hall-of-wisdom article you might gleam some nuggets of wisdom from: http://www.ducati.ms/forums/80-hall-wisdom/36038-crankcase-ventilation-system.html


The one Oronero is selling through his blog looks like this:

[koko64]

Some classy carbon cavities there.
Nice to see some close ups of what I've seen in books.

[koko64]

A major fail on transfering the photo of a photo to my computer. The best I can do is text it to you straight from the phone. PM me if that's cool.
The hose out of the back of the WCM bikes breather tank looks like it was purchased from the local hardware store. I love it coz it looks like something I would do.

[Bill in OKC]

My understanding is you want to remote the valve to the DP box and put a filter on the outlet so you don't pressurize it.  (some bikes having a pressurized airbox)