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Airbox here, one of my bikes didn't (ran to a catch can) when I got it and it was a mess, oil everywhere in the tail.
 

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Discussion Starter · #4 ·
Do you think there's any performance to be gained by not having it go to the airbox? Some of the crankcase pressure is probably blow-by, and that portion of the gas contains no oxygen, which means it can't be used for combustion. So why suck CO2 blow-by into the intake?

Or, if there is performance to be gained, do you think it's only a negligible gain for an engine that's running well?
 

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it's only a negligible gain for an engine that's running well?
If you meant creating a vacuum in the crankcase for performance benifits here is an example of how race engines for cars use vacuum pumps for the crankcase vacuum to increase efficiency.
http://newyork.craigslist.org/mnh/mcy/3218513728.html

but where the crankcase vents to the airbox there should not be any significant vacuum and the blow-by will not help combustion a second time
 

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You can put on an aftermarket tube filter if you really want to take it out the air box, some look fairly cool, depends on how it's done and where you locate it..
 

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Airbox...you would gain nothing doing anything else and probably weigh more doing it....
 

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Catch can with a foam breather....... Show me one pro racebike where they route the crankcase fumes into the airbox. Those fumes are taking the place of oxygen. Less oxygen = less power. Not to mention throwing another variable into your air/fuel ratio. And you have to have a catch can anyway so mine did actually weigh less than the stock configuration.
 

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FYI (at least on the gen1) the small box attached to the larger airbox is exatly what TGold mentioned....only thing it has elsewise is the gasketed port to the airbox

(I use a stock one for the superbike per one Zoran as the best way to work with flatslides)
 

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Discussion Starter · #12 ·
Catch can with a foam breather....... Show me one pro racebike where they route the crankcase fumes into the airbox. Those fumes are taking the place of oxygen. Less oxygen = less power.
Well that's exactly what I was thinking (blow-by fumes replacing oxygen), but apparently a lot of people think it's negligible.... who knows until you try it i guess.
 

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The one neg I figured out.... when I blew my motor last weekend - lots of oil into the airbox/filter/tb's.....
 

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but apparently a lot of people think it's negligible.... who knows until you try it i guess.
Most people are running really old street motors that have also been raced 5 seasons without a refresh.
The .5 horse increase isn't helping them(at least not enough to matter).
 

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Most people are running really old street motors that have also been raced 5 seasons without a refresh.
The .5 horse increase isn't helping them(at least not enough to matter).
Agreed, but there are some people who like to pay attention to little details (especially if the cost is low) ;)
 

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I ran the crank breathers into the PAIR valve intakes on top of the heads hoping to create some type of vacuum. Didn't do anything and my oil seemed to get dirty faster so I put them back into the airbox.
 

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Bringing this thread back, I am re-configuring the catch can for my race bike (sorry Timm ;))

The problem I have with the existing catch can is every time I lowside the can dumps oil all over the bike. Now I know the easy answer is to stop crashing but given my track record it's going to happen again at some point.

So, basically what I plan on doing is mounting some nalgene bottles to the fairing stay and running new breather hoses from the crankcase to the bottles. The bottles will have lids that have been fitted with a barbed connector so the hoses will have a tight fit. This way if I ever do crash the oil will stay inside the can and will not leak out.

Will I have any problems mounting the catch cans this way? Once oil actually gets into the can it will not be able to drain back into the crankcase. The way I envision it the cans will be air tight is that a problem? Also the way I am going to run the lines is have one coming off each cylinder where they will connect to a y-type fitting then have one line running to the catch can.

Edit - This is a picture similar to what I plan on doing:

 

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Yeah that's what I was afraid of, will wind up figuring out a way to vent the catch cans.

Edit - So since this is the first time I am dealing with a crankcase vent I figured I would ask people that know more about this stuff than me. Can I use something like an MX bike gas tank vent tube like this:



or will I need to use a larger vent? I'm not sure how much air gets pushed into the catch can, hence the question.
 
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