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Buell Forum » Knowledge Vault (tech, parts, apparel, & accessories topics) » Engine » Breathers (crankcase breathing system) » José, Blake, and others discuss crankcase Breathers? « Previous Next »

The following was pulled from the "Quick Board: 2002 Buell engine speculation:" pages.

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José_Quiñones
Posted on Wednesday, May 02, 2001 - 09:34 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Actually, the push rod covers improve the engine breathing (to help minimize puking out the breather bolts).

Remember, when the piston goes down, the air underneath the pistons is pushed up the pushrod tubes to the umbrella valve, etc.

What's easier, to push this air up two small straws or up one that's larger than both combined?
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Blake
Posted on Wednesday, May 02, 2001 - 10:27 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Jose: Amigo, you ain't been listening...

Imagine in your mind's eye the following:

First stroke of the engine... pistons go down... pressure builds in crankcase... air is pushed out of breather... umbrella valves close.

Next, the pistons go up... now there's vaccum building in crankcase.

Next, the pistons go back down... with no blowby, no pressure in crankcase builds, so no breather "air" exhausts.

Breathers are for blowby during the power stroke same as for your car engine (PCV valve) that has constant crankcase volume. I learnt this from Mr. Dickey.

Butterfly valves = PCV valve?

Besides, there ain't that much breather exhaust to overtax the capacity of four pushrod tubes is there? After all, the breather exhaust line on my bike is only a 3/8" fuel line, and just one of the four pushrod tube's annular area likely exceeds that of the 3/8" fuel line.

Loki! Glad to see you back. Hope I get to Detroit some time so's I can take advantage of your hospitality. :)
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José_Quiñones
Posted on Thursday, May 03, 2001 - 07:15 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Blake, read this:
Crankcase Breathing System
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José_Quiñones
Posted on Thursday, May 03, 2001 - 07:19 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I'll re-type it in case you can't read it:

On piston downstroke, a mixture of crankcase air and oil mist is vented up the push rod covers(1) through and umbrella valve (3) in each middle rocker box spacer.

Boy this scanner sure has come in handy.....

The comment about the new covers improving internal engine breathing is from The Battle 2Win with the Blast on the Cover (Vol 3, issue 3 I think).
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José_Quiñones
Posted on Thursday, May 03, 2001 - 11:55 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Yes, I think that's your picture, Travis. I had scanned a closeup of the picture only, not including the text. Sorry.
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Blake
Posted on Thursday, May 03, 2001 - 06:11 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

José, I respectufully disagree with the text you posted. What exactly is "crankcase air" anyway? Yes, "blowby" gasses and any oil mist going along for the ride will be expelled from the crankcase during downstroke. My point was meant to convey that it's blowby, not fluctuation of crankcase volume, that mandates the existence of a breather system. Otherwise, car engines, having constant crankcase volumes, wouldn't need breathers, would they?

As to the Blast pushrod covers... I don't buy that fluf; even a big V8 uses pretty much the same size tubing for a breather line. Ever removed the oil filler cap from a V8 while it's running? It's surprising how much exhaust spews out.

My take is that the Blast covers were designed to be atypical/non-HD in form and also very cost effective. Improved engine breathing sounds good though don't it? Just my opinion, I could be totally wrong. I enjoy the discussion in any case. Even without any math :) .
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José_Quiñones
Posted on Thursday, May 03, 2001 - 09:55 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Blake,

So you are disagreeing with the people who wrote the FACTORY SERVICE MANUAL? The people who designed the motor? Ok.

Do you have a factory service manual handy?

Here's how it works. You see, the push rod covers actually serve two functions:

1. To vent out crankase air/oil up them to the breathers when the pistons go down. page 3-34

2. To allow oil that was sent up to the heads to lubricate the rocker arm shafts and bushings to go back down to the crankcase! Page 3-35.

You see what's happening here? Two opposite things are trying to happen in the pushrod tube at the same time:

1. You have all this rocker arm oil trying to get back DOWN to the crankcase

2. But the crankase air pushed by the downstroke is going UP the same PUSHROD TUBE, so what happens at high rpm is that the air keeps this oil in the heads, and it pukes out the breather holes!

The reason the Blast! is an improvement is that it provides more space/volume for these two opposing events to happen. So there should be less puking out of the breather valve of a Blast!, theoretically.

I'll quote the Service manual directly if to see if it explains it better.

Oil System page 3-35
Step

11. Oil flows up passages in the push rods to the rocker arm shafts and bushings.

12. The valve stems are lubricated by oil supplied through drilled oil holes in the rocker arms

13. Oil collected in the push rod areas of the cylinder heads flows down the push rod covers, through drain holes in the tappet blocks and into the gearcase.

So that's what happening, you got oil trying to get down the push rod tubes, and at the same time you got crancase air trying to go up the same tube. No wonder these bikes puke!
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Blake
Posted on Thursday, May 03, 2001 - 11:20 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

José: See, I said I could be wrong. :) I was wrong!... About the blast breather design. I'll stick to my point about blowby though; it ain't anything close to being "air."

Not sure who wrote the service manual; not likely it was the same person(s) who designed the engine though.

I had no idea oil was trying to dribble back down the pushrod tubes. I guess the few bikes I've seen with no pushrod tubes have some other return path for that oil. Guess that answers your question about my service manual. It's on order though, and I have a PDF of the old S1 manual (thanks tripper, it'll be online soon).

Thanks for setting me straight.

Blake (still has lots more to learn too)

PS: Wait one second... if, per Randell Hendricks, simply drilling out the drain hole in each rockerbox solves all oil pukage problems; what does that say about needing bigger pushrod covers? Maybe I ain't so wrong after all?
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José_Quiñones
Posted on Friday, May 04, 2001 - 07:47 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Boy this would make excellent FAQ material!

Q. Why does my Sportster/Buell Puke oil into the Air Cleaner?

A. Study the following diagram from the Service Manual:

Oil System Circulation Diagram, page 3-35

Follow the steps:

11. Oil flows up passages in the push rods to the rocker arm shafts and bushings.

12. The valve stems are lubricated by oil supplied through drilled oil holes in the rocker arms

13. Oil collected in the push rod areas of the cylinder heads flows down the push rod covers, through drain holes in the tappet blocks and into the gearcase.

14. Feed oil to the rocker area is returned to the crankase through a passage in the head and cylinder.

At the same time, look at the diagram and read the following from page 3-34:

On piston downstroke, a mixture of crankcase air and oil mist is vented up the push rod covers(1) through and umbrella valve (3) in each middle rocker box spacer.

You see what's happening? You have oil trying to get down the push rod tubes, and at the same time you got crancase air trying to go up the same tube to vent out the breather bolts. No wonder these bikes puke!
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José_Quiñones
Posted on Friday, May 04, 2001 - 08:08 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

breather setup closeup for the FAQ

Blake,

Drilling the hole larger simply allows the oil to drain faster. I don't think it eliminates it completely, but it certainly helps.

Define Blowby.

Is this blowby below the rings? That goes into the crankase to get vented out.

Or is it oil blowby from the crankase across the rings into the heads? That stuff ends up going out the exhaust valve to the pipes. If you have ever seen inside a set of headers from a bike with bad valve seals or worn rings, you'll see what a mess is in there.
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Blake
Posted on Saturday, May 05, 2001 - 05:13 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

José: The blowby I'm referring to is exhaust that (under combustion pressures that can exceed 1,000 psi) makes it's way from the combustion chamber, past the rings and into the crankcase. This blowby occurs increasingly with power/throttle level, just like in your car. Your car most likely has a constant volume crankcase (the sum of crankcase volumetric change due to piston motion is zero). So the only thing pushing crankcase exhaust spewage through the breather/PCV (pukage control valve :)) is the blowby itself.

As you point out, you can also get blowby (really "suckby"? :) ) in the reverse sense. Suckby can show up as a brief very light puff of smoke at your tailpipe, but this should only happen under high rpm engine braking/deceleration. It's initiated during the intake stroke when, with a closed throttle, the vaccum created inside the combustion chamber sucks oil and (okay, I'll say it) crankcase "air" (grrr) up past the rings where it next gets ignited, burned, and sent on it's way out the tail pipe. It happens more in a hot/loose aircooled engine. You can often see this at the completion of a dyno run when the operator let's the throttle snap closed.

I have seen how oil in the exhaust can make a real mess, kinda like some piston domes and head chambers I've seen where the breather was left in stock configuration allowing oil mist to contaminate the combustion chamber. Here's a "thinking outside the box" idea... leave the breather spewing into the airbox, but use a two stroke oil? Heheheh.

That closeup is great, but palease, don't post that dang blurry little pic again! There must be a dozen of those floating around the board.

This brings up a little trick that Vik/eeeeek may not even have figured out. If you want to include an existing board pic in your post you can fool the BBS software as follows:

Copy the filename (no extension) of the pic of interest (in MSIE simply right click and pick "Properties" then highlight and copy only the filename portion of the URL, the part that follows last "/"). This will look like (in the case of José's pic above) "6415". Then, instead of posting a new copy of the same old existing pic using the

\image{text descripton here} command

use the following formatting command...

If the pic is in the same main topic (one of those shown on the main tipics page) where you want to repost it then...

for a GIF use...

\image_alreadyuploaded{filename, text description}

For José's pic above you would post...

\image_alreadyuploaded{6415, Breather Circuit}

You get this...

 Breather Cicuit
notice my text description is different.

for a JPG use...

\jpeg_alreadyuploaded{filename, text description}

Like this for one of José's previous pic posts...

 Tilley's Racing Buell

For pics resident within other main topics, simply add the portion of the pic's URL that follows ".../messages" and preceeds the filename. Then tack a ".." in front. For my dyno chart pic on the dyno chart page the formatting would look like...

\jpeg_alreadyuploaded{../3842/6323, my stockish '00 M2}

And you get...
 my stockish '00 M2

This will be most appreciated as it will save on valuable disk space and bandwidth.

Blake (not riding cause I got no Bike in NJ... yet!)
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José_Quiñones
Posted on Sunday, May 06, 2001 - 08:08 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I actually tried to do that with the blurry Breather picture, it's 6402, I think. It didn't work in my original post because I didn't know about jpeg_alreadyuploaded, so that's why I reposted it. That is a great tip, thanks.

The reason that breather pic is blurry is because it was the only way I could get it around 30k. I'll try to scan it again and see if I can get a better quality pic.

_________________________________________________

Yes, the blowby you are talking about goes into the crankcase and is vented out the breathers. But I don't think it is a major component of the crankcase air.

So the only thing pushing crankcase exhaust spewage through the breather/PCV (pukage control valve ) is the blowby itself.

No, the pistons moving down move the air up the pushrod covers to get vented out the breathers.

If all that air coming out the breathers was only caused by blowby, you would have no compression!

A Buell engine is not different from a car engine, it is also a constant volume crankcase.

So it's just regular air in there. Otherwise you would have a vacumm

So this air, plus any blowby, needs to go somewhere, so when both pistons are moving down, the air goes up the pushrod covers to get vented out the breather bolts. But at the same time, as you now know, oil is trying to return through these pushrod covers back into the crankcase, but at high rpms it is actually being puked out of the breathers. Moving air, at that speed, can move anything, especially a liquid (waves on the ocean)

Those pushrod covers do get a work out
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José_Quiñones
Posted on Sunday, May 06, 2001 - 09:56 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

here's a better one

Breather Diagram
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Aaron
Posted on Sunday, May 06, 2001 - 10:30 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Jose', you're a sharp cookie and I really enjoy your posts, I've learned a thing or two from them. But I think Blake is right on this one.

In most cars, for every downward piston movement there's another piston moving up at the same point in it's cycle. Hence the volume of the crankcase doesn't change.

Not so in a 45 degree common crankpin motor. There's 90 degrees out of 360 where one piston is moving down and the other piston is moving up (45 at bdc and 45 at tdc). The other 270 degrees, they're moving the same direction. No? So the volume of the crankcase is constantly changing.

Then they stick these one-way valves on the breathers. So when the volume of the crankcase is at it's minimum level, and moves towards it's maximum, it pulls a vacuum.

Seems to me that beyond the first pass through minimum crankcase volume, what's coming out the breathers is just blow-by. Assuming the umbrella valves are working of course.

Does this make any sense?

AW
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Chuck
Posted on Sunday, May 06, 2001 - 02:03 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Let's ask Erik
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Blake
Posted on Sunday, May 06, 2001 - 08:09 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

José, what Aaron said!

Aaron, check's in the mail.

Chuck, Erik just called, said he would completely and honestly answer any one question that I had. He said Aaron was correct. (Sorry Rocket)

Blake (picturing the lightbulb beginning to glimmer over José's head) :)
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José_Quiñones
Posted on Monday, May 07, 2001 - 07:25 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Aaron,

The other 270 degrees, they're moving the same direction. No? So the volume of the crankcase is constantly changing.

I agree.

What I meant by quoting Blake with the Constant Crankcase Volume is probably more accurately described as, constant engine volume, ie the volume in the cylinders + crankase remains equal.

But if you don't vent the crankcase you would presurize the crankcase. So this air has to go somewhere when the pistons go down, so they vent out the push rod covers to the heads.

I think it's pretty well established that the puke oil is the oil that was trying to get back into the crankcase from the heads through the push rod covers that is getting blown out by the venting air trying to leave through the same push rod covers.

Where I don't agree with Blake is that the blowby is the only air that you feel coming out of the breather hoses. What you feel is the crankcase air (including some blowby) displaced by the downstroke of the pistons.

While idling I can feel the breather hose flow reverse, it blows out then stops/inhales then blows out again.

The umbrella valve doesn't seal completely, and besides the valve you have the DRAIN hole, which is small, but it is still a hole.

Anyway, I'll stick to my guns on this one till Erik/Gary Valine/Henry Duga/R chime in.
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Rickie
Posted on Monday, May 07, 2001 - 12:06 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Jose,

If it makes any difference in your hypothesis, there are four crankcase breather/oil return passages in each head. Two are the ones you refer to, and the others are in each valve spring pocket. The service manual references them as # 14 in the diagram you posted from page 3-34.
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Blake
Posted on Monday, May 07, 2001 - 12:21 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

José:

I guess Ron Dickey of Axtell lied to me and/or doesn't know what he is talking about (YAH! RIGHT!). Believe whatever makes you happy.
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José_Quiñones
Posted on Monday, May 07, 2001 - 01:02 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

MikeJ

Gary Valine is pretty much responsible for the current Thunderstorm motors. He works for Buell as an engine development & testing engineer.
_________________________________________________

Rickie,

Yes, that is the other path for the oil to return to the crankcase. The oil that tries to go down the pushrod tubes is the one that has to fight the crankcase venting and ends up getting puked out at high RPM.

_________________________________________________

Blake

I'm happy if you are happy.

I don't think we are that far apart. I agree that blowby is part of what is being vented out. I just think that it is also regular crankcase air along with it. If it turns out that it is ONLY blowby air, then so be it. I can admit being wrong.

Someone on Sacborg ask Reg Kitrelle to ask Kip Woodring about this.
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Aaron
Posted on Monday, May 07, 2001 - 02:31 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Jose': I agree, the point really being debated is pretty damn subtle.

Here's some more food for thought ... I have a bike, won't say which one, but it will literally suck oil OUT of the primary, into the crankcase. I'm not kidding.

It has exceptional ring seal.

I've had to jump through hoops to keep it from wet sumping. It really has a hard time scavenging.

AW
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Blake
Posted on Monday, May 07, 2001 - 02:34 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

José: I am unconscionably happy right now!!! :) YEEEEEHAWWWW!!!

Question though: How would the "regular crankcase air" in any crankase get replenished other than from blowby? From where is the crankcase drawing this "air".

Again, start your car, let it warm up, remove the oil filler cap. Briefly sniff the gaseous vapor spewing forth; okay that's enough! Air?... Or exhaust fumage? Replace filler cap. Same stuff now spews out breather. Why do you think it's called a pollution control valve (PCV)?

Umbrella valves = PCV

Blake (stubborn jackass sometimes)
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Rickie
Posted on Monday, May 07, 2001 - 03:33 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Jose,

Compare the orifice that the oil return and crankcase venting share on the side of the head that you emphasize to the OTHER PATH.

Now put a garden hose and a straw in your mouth and try to breathe through them. Which is the path of least resistance and passes the most volume of air? Of course it is the garden hose, well that is the overlooked other path.
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Aaron
Posted on Monday, May 07, 2001 - 03:38 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

PCV = Positive Crankcase Ventilation
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Ron
Posted on Friday, June 29, 2001 - 09:09 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Other than going with external oil return lines, would it be possible to increase the size of the oil returns in the valve spring pockets and realize less oil puking?
This problem drives me nuts. I like to use my S-3T for long distance. I use Over the factory ordained quart per thousand yet no fix from them. So finding a remedy for this would be great! And I may just see about the external oil lines this winter. Any thoughts on that?
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Blake
Posted on Saturday, June 30, 2001 - 12:58 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Drilling out the return hole in each rockerbox reportedly greatly reduces, even eliminates puking. I cannot recall what diameter, 1/8th inch rings a bell though.
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José_Quiñones
Posted on Saturday, June 30, 2001 - 08:04 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Do what Blake said and route your lines out of the airbox and your problem will be greatly diminished.

Check out what I did in the S3 Files
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José_Quiñones
Posted on Saturday, June 30, 2001 - 08:30 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Here is probably the best solution to this problem, courtesy of Brian Nallin's Dirt Tracker:

Breather hoses go into the exhaust pipes

Notice where the breather lines go......
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Blake
Posted on Saturday, June 30, 2001 - 05:43 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

José: I thought the same thing. Unfortunately Brian advised me AGAINST a header mounted scavenging breather setup for street bikes. It's a race only configuration. Why? Brian told me that under normal riding, and especially with a muffler, that you can actually see higher than atmospheric pressure rather than a slight vaccuum. Apparently a venturi with enough efficiency to work under normal street riding conditions would need to protrude into the header too much, and the negative effect on exhaust flow then far outweighs the benefits of the breather scavenging. Plus, and more importantly, he mentioned that the inevitable oil spewage can eventually goo up the inside of a muffler and result in a tarry drippage seeping out of your exhaust and it's connections.

But if you've got a Force Streetfighter, or a KT and constantly ride balls to the wall WOT, it might be a good idea.

Great pics!
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José_Quiñones
Posted on Saturday, June 30, 2001 - 10:46 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Yes, that makes sense. Thanks for the correction.
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