Best way to route crankcase vent pics.


14 replies to this topic
  • Mikeanic

Posted March 21, 2006 - 10:01 PM

#1

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  • MotoRick

Posted March 21, 2006 - 10:15 PM

#2

I like the idea of the air break, but putting the tube in the carb boot is not so good. For one, it provides one more place to create a potential intake leak. For another, the air on that side of the filter is mostly positive vacuum under power. Under high vacuum you'd be pulling unfiltered air into the carb through that tube going under the bike. You could also be sucking the crankcase vapors right into the intake tract. While that might endear you to the EPA, it isn't the best for performance. Even with the air break, the path of least resistance would be into the carb boot. You'd be better off putting that part of the plumbing into a high spot in the airbox. Clean work, though.

  • Mikeanic

Posted March 21, 2006 - 11:20 PM

#3

I like the idea of the air break, but putting the tube in the carb boot is not so good. For one, it provides one more place to create a potential intake leak. For another, the air on that side of the filter is mostly positive vacuum under power. Under high vacuum you'd be pulling unfiltered air into the carb through that tube going under the bike. You could also be sucking the crankcase vapors right into the intake tract. While that might endear you to the EPA, it isn't the best for performance. Even with the air break, the path of least resistance would be into the carb boot. You'd be better off putting that part of the plumbing into a high spot in the airbox. Clean work, though.


I would like to clarify : The bottom hose is actually a drain and it is plugged at the bottom . It is there to accumulate excess oil/ moisture . The hose at the air boot is sealed very well . The air pressure is the same on both sides of the air filter , unless it is plugged , atmospheric pressure . If you could pull a significant vacuum on the filtered side , performance would suffer greatly .All modern performance cars and even the Honda CRF vent crankcase gasses into the intake tract . All it is , is air with possibly some hydrocarbons and moisture . I doubt that it will affect performance much . I rode it before and after the conversion and there was no noticeable difference in power . The bike rocks ! My main goal was to allow the crankcase to breath clean air and keep as much crud out of the air filtered side as possible . Dare I say that I got the idea from the crankcase vent system on the Honda CRF450 . :thumbsup:

  • Stevequest2000

Posted March 22, 2006 - 01:35 AM

#4

I remember on the older cars with the circular air filter that I owned, seeing the black spot on the air filter where the breather hose entered the the air cleaner assembly. It wasn't drenched with oil, but it was dirty enough that I would be worried of the possibility of getting something into a high performance motorcycle carb. A question I have is what happens when your bike is upside down on a hillside? Will oil seep through the breather hose from the motor?

  • cowboyona426

Posted March 22, 2006 - 09:08 AM

#5

Nice job, but it would have been 100 times easier just to run the tube into your airbox and put a small filter in the end of it :thumbsup:

  • grayracer513

Posted March 22, 2006 - 09:42 AM

#6

There is a vacuum on the clean air side of the filter, but it is very minor, amounting to barely 1-2 in/hg at high RPM, full throttle on a 450 with a dirty filter, and much less than that at less than full throttle. There is, however, a net outflow of gas through the breather under a load, so there will be crankcase gases entering the intake stream. With an engine in good health, the amount of those gases will not be enough to cause a problem, and there should be no concern about "stuff" coming from the crankcase that would be a danger to the top end.

There is a performance gain associated with pulling a vacuum in the crankcase for the same reason that the crankcase is vented in the first place. The air under the piston gets in the way, and if the crankcase pressure is lower, there's less air in the way than at higher pressures. This breather arrangement won't really accomplish much of that, but it won't hurt.

High performance, or for that matter, all cars vent crankcase gases into the intake manifold at low throttle positions, drawing fresh air into the crankcase through a small filter. At heavier throttle, the flow to the intake is shut off, and the crankcase gases are vented to the outside of the air filter, not the clean air side (in most cases), so that comparison doesn't really work.

The upside-down bike scenario represents a valid concern, but any such oil intrusion should be fairly minimal considering the fact that YZF's are dry sump, and the difficulty of moving oil past the baffling in the cam cover, etc. And, of course, the point about creating a possible leak in the air boot should not be brushed aside lightly. That could be trouble if the hose fell off.

Overall, I'd say you did an excellent job on this, but I'm going to have to agree with the Cowboy on this one; just run it into the air box, outside the engine air filter, and put a small filter on the end.

  • MotoRick

Posted March 22, 2006 - 10:37 AM

#7

High performance, or for that matter, all cars vent crankcase gases into the intake manifold at low throttle positions, drawing fresh air into the crankcase through a small filter. At heavier throttle, the flow to the intake is shut off, and the crankcase gases are vented to the outside of the air filter, not the clean air side (in most cases), so that comparison doesn't really work.

Exactly right. The systems on cars use a PCV valve to control crankcase vent operation. There is no similar setup in this situation so the vent circuit is active all the time. Like I said, this was a clean mod, but my main concern is the attachment to the carb boot itself. A slipped hose, an aging fitting, soft, flexible rubber can all lead to an intake leak. It would have been much better to have vented it into the airbox, IMO. This is on an '04 WR450, but the process is fairly equal on any YZF/WR:
http://www.mcjournal...-0605_page3.jpg
http://www.mcjournal...-0605_page4.jpg
I'm not saying the way the OP did his is bad, but calling it the "best" way is a stretch. Because of the many different ways we ride, types of environments we ride in and the ways we wash our bikes, there probably isn't any one "best" way to do this mod. Seeing various methods and figuring out which is best for you is a good thing. :thumbsup:

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  • NYMXer

Posted March 22, 2006 - 12:19 PM

#8

I just ran mine into the airbox w/o a filter at the end. I'm afraid that the little filter bouncing around will tear my air filter while riding. :thumbsup:

  • MotoGoalie

Posted March 22, 2006 - 02:42 PM

#9

Overall, I'd say you did an excellent job on this, but I'm going to have to agree with the Cowboy on this one; just run it into the air box, outside the engine air filter, and put a small filter on the end.


WHAT? :bonk:

Like this. :thumbsup:

Posted Image

theres a little PVC filter on the end of it. :thumbsup:

  • black_n_blue_thumper

Posted March 22, 2006 - 10:35 PM

#10

It wasn't drenched with oil, but it was dirty enough that I would be worried of the possibility of getting something into a high performance motorcycle carb.

I wondered about this as well, until the last time I cleaned my air filter. It had a small spot of oil on the outside of the filter, but when I looked to the inside of the filter, nothing. All of the oil (actually very little oil) was getting trapped in the filter, not passing through. I am now alot more comfortable with this setup. :thumbsup:

  • lipskid

Posted March 23, 2006 - 07:18 AM

#11

I haven't re-routed, but did make a small, serviceable filter out of pvc fittings, screen, and PCV filter material. I did so after finding a few grains of sand in my oil filter. I have looked at Honda to see how they did it(I'm to lazy). VERY nice job Mike. Looks "factory". :thumbsup:

  • MotoRick

Posted March 23, 2006 - 10:33 AM

#12

I remember on the older cars with the circular air filter that I owned, seeing the black spot on the air filter where the breather hose entered the the air cleaner assembly. It wasn't drenched with oil, but it was dirty enough that I would be worried of the possibility of getting something into a high performance motorcycle carb.

Bad comparison. The air filter on a car has a paper element that's designed to be dry. Your bike's air filter is foam and designed to be wet with oil. Having a tiny amount of oil-laden crankcase vapors drip onto the outside of your bike's air filter will do absolutely no harm. It's already wet with oil to begin with. And if your bike were to be inverted, it would have to be that way for a considerable amount of time for what little bit of oil is in the top end to work its way into the breather hose to become a problem.

  • Stevequest2000

Posted March 23, 2006 - 07:25 PM

#13

I was not referring to routing it into the airbox outside the filter Motorick, you took that out of context. I was referring to routing it straight to the carb as the very first pictures in this thread showed. I have mine routed to the airbox. Most think that it's okay to route it straight to the carb and that may be fine. I was just playing it safe with my routing.

  • Stevequest2000

Posted March 23, 2006 - 11:11 PM

#14

By the way, I'm not sure how the dry sump system works or anything like that, but when I blow on the end of the breather hose, the air will come out of the drain holes, filler cap, or whatever motor orifice is open... I just figured that if I could blow into the oil supply, at some angles that oil could make it's way down the breather tube and into the clean air side(if that was where the breather tube was vented). I'd be concerned with wrecks where the bike is on hills or off cambers, upside down.

  • SureBlue

Posted March 24, 2006 - 01:49 AM

#15

By the way, I'm not sure how the dry sump system works or anything like that, but when I blow on the end of the breather hose, the air will come out of the drain holes, filler cap, or whatever motor orifice is open... I just figured that if I could blow into the oil supply, at some angles that oil could make it's way down the breather tube and into the clean air side(if that was where the breather tube was vented). I'd be concerned with wrecks where the bike is on hills or off cambers, upside down.


Steve, I don't think the oil finds its way easily to the breather hose in dry sump engines, UNLESS you have dramatically overfilled the engine with oil.
In any case, I find it better not to route the hose to the clean air side.





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