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Buell Forum » Knowledge Vault (tech, parts, apparel, & accessories topics) » Engine » Breathers (crankcase breathing system) » Breather Routing Question « Previous Next »

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Posted on Sunday, November 22, 2009 - 11:21 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I am another FNG here (picked up my 08 Uly a week ago) and have read a LOT of impressive info here I still have one lingering question. While this was going to be THE bike I wasn't going to screw with, it appears I lied to myself again.

The most common ( almost necessary ) mods seem to be the crank vent reroute and of course the exhaust. While I haven't gone so far as to investigate the complete routing of the vent system I am still left wondering why no one has added a nipple on the exhaust and routed the vent there.

Here is how my distorted logic plays out in my mind, please show me the error in my ways. ( I have been called a moron before lol)

1) The discharge vapor which is minimal anyway would be heated to the point of steam and ejected out the exhaust. We are already discharging approx a gallon of water vapor for every gallon of fuel we burn as a by product.

2) If at the same time we create a vacuum, through a venturi effect of the exhaust, that we can utilize to reduce the crankcase pressure we actually enhance our engine performance. If the vacuum is excessive I can install a relief valve inline. NASCAR and NHRA already use vacuum pumps for this purpose and basically use a dry sump system like we are looking at.

Just some early Sunday morning thoughts from an FNG. My ECMspy arrived yesterday, anyone with an 08 have the perfect map?? LOL It's all new to me.
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Posted on Sunday, July 11, 2010 - 10:14 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Not such a bad idea. I just may try it.
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Posted on Monday, July 12, 2010 - 07:57 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Here's some info on topic:
"There I go again, letting out all the hot engine building secrets. Oh well, now that the cat is out of the bag I guess I'll have to tell you about breathers and suckers.

To start, you must realize that your engine is an air pump, and the piston(s) pump air on both sides of the piston crown. If you have a single, the piston is pumping 6-800cc of air in and out of the crankcase breather. Pumping air expends energy. If you are pumping air in and out of the engine through a tiny little breather it takes even more energy, because the small hole is more restrictive. If you build up the crankcase pressure by the air not being able to easily escape, it will try to escape wherever it can. This is the cause of many of the small oil leaks - oil isn't seeping out of the engine, it is being forced out. The internal air also tends to have a lot of oil in it, and oil suspended in the air isn't being pumped by the oil pump.

If you install a check valve on the engine breather(s) the air that is pushed out by the falling piston can't be sucked back in through the breather. It has to come in past the oil seals/gaskets/rings. The amount of air that come from these places should be much smaller than the amount the piston can force out past the check valve, resulting in a reduction of air in the cases after a few revolutions of the crank. The car guys found out that if they ran the breather hose from the check valve to the exhaust pipe, the exhaust rushing by the attached hose would help to pull the air out past the check valve, adding an additional extractor effect to the check valve. Exhaust sucker sounds so much more entertaining than an exhaust extractor, eh what?

I use a Standard Motor Products AV13 check valve. This is a metal bodied, spring loaded rubber diaphragm automotive PC valve. The engine side has a hose barb of about 7/8" OD, and the exhaust side has a big heavy nut brazed to the body. You could screw a pipe fitting into the nut, but I cut them off and make a lighter hose barb and weld it to the valve body. This must be done carefully as you don't want to melt the rubber seal. I set the valve in a bowl of water and make a bunch of short TIG welds, allowing everything to cool down between welds. The exhaust pipe attachment is a bit of steel tubing of a size to match your hose barb. Weld this to the head pipe near the manifold/collector and drill a .125" hole through the pipe. Melting of the hose doesn't seem to be a problem. The car folks found that you can overdo things here, as with larger sucker pipes pointing "downstream" in the exhaust they were able to get enough of an extra suck to where they started to pull oil from the engine.

The car guys have reported this type of system developing 4-5 inches of mercury vacuum. When Bill Jenkins wrote about this in 1976 in "The Chevrolet Racing Engine" he said that the only thing stopping them from pulling more vacuum was the lack of a better mainseal. Sometimes engines require the seals to be reversed, as the problem is keeping air from coming into the engine, not keeping oil from going out! (Yes Stan, you should have bought the book and read it - then you to could represent yourself as an engine guru by passing along someone else's hard won information).

I figure that even if this just breaks even on power, it is worth the time to reduce the likelihood of the pesky oil leaks. My TT500 road racer once developed enough internal pressure at Sears Point to where it pushed the countershaft seal out, liberally lubricating the left side of the rear tire going through Turn 1.

My friend Craig also thinks it is worthwhile to eliminate rocker cover breathers, and use just a crankcase breather. He theorizes that air rushing to get out of the rocker cover breather may slow the return of oil from the head to the crankcase. We don't have any proof of this, but it sounds reasonable, and if you run the valve/sucker you will only need one breather outlet anyway."
- Michael Moore
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