Crankcase vent vacuum setup removal = bad

[junior varsity]

pods is fo' looks, certainly not for performance

[ducatiz]

pods is fo' looks, certainly not for performance

necessary for short manifolds.  looks?  ok.

[junior varsity]

not necessary!




and from Jako's Super-Due:

[ducatiz]

not necessary!




and from Jako's Super-Due:

interesting, they made tubes to extend the throat.

[junior varsity]

on the top two.

the bottom one he molded his own carbon fiber airbox that goes around the split singles and really benefits from still having 'tuned' (length chosen for particular power curves) velocity stacks and a big volume.

[koko64]

The air velocity in the 2V airbox is not that high.  If you open up a few holes on the cover, the flow is in the order of less than  16 MPH at 9K RPM.  If the airbox velocity is less than air velocity around the bike when it is moving, using it as a source of vacuum may be silly.  You may be better off using a venturi with the faster airflow down the sides of the bike.

You must do two things, vent the excess pressure from the crankcase (or your bike will turn into a Triumph, and no offense intended), and not allow any oil to leak into the rear tire.  Anything else is gravy, driven by practical considerations.

If you do not want to carry the canister, don't.   I have a long hose from the crankcase reed valve to the rear of the bike, capped with a low pressure one way check valve.  The check valve allows the positive crankcase pressure to vent to a low pressure area.  I don't use a filter, gas flows out.  The long hose helps some of the oil vapors to condense and fall back through the drain hole in the reed valve.  Haven't checked to see if the hose holds a slight negative during piston rise, but it probably is better than the stock setup.  Some superbikes do something similar, gutted the reed from the crankcase and connected the hose to a second one way valve and then that to the airbox.



 

Hmmm.. Food for thought. Did you measure this?
So an open air box negates to some extent the vacuum draw on the crankcase?
Is it still worth using the stock breathing system with an open air box, as far as applying vacuum scavenging to the crankcase goes?
What about the system you describe with a hose to the rear of the bike from the stock 'baffle box'?

[scott_araujo]

interesting, they made tubes to extend the throat.

You mean the orange velocity stacks in the air box?  These are really important and effective for minimizing turbulence in the airflow.  Even these relatively short ones can change the airflow drastically.  If you look in the stock airbox it has velocity stacks molded in.

As a side note, it's often much better if they have a fat, rounded lip rather than the relatively sharp edge created by just pressing metal into a horn shape.  Again, turbulence is greater over the sharper edge.

Scott

[junior varsity]

You mean the orange velocity stacks in the air box?  These are really important and effective for minimizing turbulence in the airflow.  Even these relatively short ones can change the airflow drastically.  If you look in the stock airbox it has velocity stacks molded in.

As a side note, it's often much better if they have a fat, rounded lip rather than the relatively sharp edge created by just pressing metal into a horn shape.  Again, turbulence is greater over the sharper edge.

Scott

No, the adapters from the carburettors to the airbox itself - the u-bend is on the side closest to the airbox so that the carbs can still be on short manifolds to the head.

[koko64]

You mean the orange velocity stacks in the air box?  These are really important and effective for minimizing turbulence in the airflow.  Even these relatively short ones can change the airflow drastically.  If you look in the stock airbox it has velocity stacks molded in.

As a side note, it's often much better if they have a fat, rounded lip rather than the relatively sharp edge created by just pressing metal into a horn shape.  Again, turbulence is greater over the sharper edge.

Scott

I have a set of shortened stock rubber stacks from a carbed Monster. I haven't tested them as yet. They have about the same shape and radius as the stockers, but the trumpet sits flush with the base of the air box. The expected advantage is that they sit further from the air filter element and help hold the torque peak for longer, but we will see if the shortened length has any drawbacks with the power curve and turbulence.

[koko64]

I had a look (again) at some of the info from the Nichols site and went over some of the links from threads here.

Came to the conclusion that venting to as large a cavity as possible at less than atmospheric pressure is still the best way to go. The bigger the cavity on the crankcase side of the filter medium protecting it from the atmosphere the better.
Since the air box adds to the overall volume in addition to the breather box/oil separator, this helps to add to the crankcase volume to reduce pumping losses.
Also, even slightly lower than atmospheric pressure in the airbox is of some help.

So three things to consider besides aesthetics, venting to large cavities that extend crankcase volume, having some vacuum assistance to bring cavity pressure to below atmospheric pressure, and venting safely in the event of oil spillage.
I'll stick with the stock system (although the plumbing annoys me).

[koko64]

Just out of interest, I'm looking at page 36 in Ian Falloon's book "Desmoquatro Superbikes".

There is a picture of an 1993 888 Corsa with the body work off. It has a large volume hose from the crankcase breather running to that Corsa style breather cavity that people have mentioned. The cavity is over a foot long. The cavity nearly runs the length of the rear guard under the tail area. It has another hose running back to the air box.

I don't know if the factory was using full ram air by then or fresh air to an open airbox.

[booger]

OK so lightly skimming the entirety of this thread, I'm left with the understanding that removing the breather box is a detrimental endeavour. A diminished return.
I've been playing with the idea of buying a Hypermotard for a couple of years now. I love those bikes, fun fun fun. However the big problem with the HMs is the fuel capacity. ~90 miles a fillup, bad bad bad. I'm the type of person who would be out having fun fun fun then run out of gas because motorcycles don't tend to have fuel guages, just low fuel warning lights. Keeping an eye on the trip odo is easier said than done, and inaccurate when you're out doing wheelies and other hooning activities out in the middle of nowhere. Since I like to ride out in the sticks to stay away from grosse traffique this could end up in a situation where I'd have to push the bike which would not be a happy day. Just like doing everything I can to avoid crashing, I'd like to also do everything I can to avoid being stuck on the side of the road. Some say it's an inevitable side effect of riding, I say screw that I don't ever want it to happen to me.
There seems to be a solution - the CA Cycleworks Hi-Cap fuel tank. Chris is quite a crafty problem solver. But this requires going to pod filters in lieu of the stock airbox and deleting the breather box as well to provide the space for the high capacity fuel cell.
So what now? Carry a jerrycan on the back of the Hyper?

[hunduc]

i'm still not sure how detrimental it is. what, you lose a couple horses? i doubt we ride our bikes to the limit - not even close. if you are worried about spitting oil on the back wheel, just move the filter higher or to the side. so many people did this mod, and we have a couple who don't like it.

what's wrong with a jerrycan, btw? or maybe you could use those backpacks which are for hydration for cyclists, just put gas in it.    

[koko64]

I reckon you should consider the TPO kit as it has velocity stacks in the pods, and run them under Chris' tank. I hope they fit because that's what I would do. The most important thing is to have a well designed velocity stack/trumpet inside the filter whether it be a pod or panel filter in an airbox.

There is also the issue of whether you could run a well designed velocity stack within a cut down air box. No harm enquiring with TPO. If the airbox has to be removed completely for a bigger gas tank then run pods. It's all about compromise. It's what gives the best net performance gain on a practical street bike. I've seen the film "Deliverance" and I wouldn't want to run out of gas in the middle of nowhere!

I'm guessing that you would gain more from that set up than you would lose from venting the crankcase to the atmosphere. With the right fueling you might gain 5-10hp from the TPO Beast set up and lose one from the crankcase set up. You are still ahead by a mile. The main thing is to not get oil on your back tyre or have engine leaks. I would still run the vacuum hose to an oil separator box or racing style catch tank to add to crankcase volume and protect your rear tyre from oil when you wheelie. It wouldn't be connected to an airbox but it would vent to the atmosphere via another cavity.

I only run the airbox because that 1 hp is important to me as I don't have many to spare! Come to think of it I'm going to do a dyno run with and without the crankcase hose connected to the airbox to see exactly how much difference it makes.

I am in the process of organising a dyno test for a carbed M900 which compares pods to airbox, and airbox with short rubber stacks verses stock rubber stacks. When I test the pods I will of course run the crankcase breather from the cavity under the seat to the atmosphere. I will still have the extra volume of the oil separator box cavity.

If pods or airbox give better performance then I will convert my bike and my friend's bikes to the 'winning' set up. Then I will do the same for customer bikes once I know the truth. The testing I am going to do relates more specifically to carbed bikes so I look forward to seeing what you choose to do and how it works. For my money Ungehuer is running WASP velocity stacks and pods with modified fuelling and his bike sounds like it is very, very strong. Hopefully we will test it also. I think the TPO set up is similar and if I had an 1100 or 1000DS I would try it.

[He Man]

pods dont hurt if you have a velocity stack. If properly sized, its almost unnoticeable.