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  #1  
Old 09-15-2009, 06:52 PM
N941WR's Avatar
N941WR N941WR is offline
 
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Default Plumbing oil breather line to the exhaust?

A friend has recommend that I have a fitting welded to my exhaust and plumb my oil breather line to that fitting.

What are the pro's and con's (other than modifying the exhaust) of doing this?

Have any of you done it? Does it cause engine leaks, etc.?

(My friend said it creates a vacuum on the engine and stopped all of his oil leaks.)
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  #2  
Old 09-15-2009, 07:45 PM
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Ironflight Ironflight is offline
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Where's your breather exhaust now Bill? Van's recommendation (at least I think it's their recommendation - most every RV I have seen with a breather pipe does it...) is to end it just ABOVE the exhaust, so that the burped oil (at least some f it) burns off on the outside of the pipe.

Running it in to the exhaust itself? Hmmm....I'd have to see quite a few folks who'd done that first before I'd be convinced it was a good idea (yeah, I'm pretty cautious). Not knowing the pressure in the exhaust pipe, I'd not know if I was pumping hot gas into the engine, or siphoning oil out.

Look at it this way - If it was an easy cure-all for belly oil, everybody would already be doing it, wouldn't they? (Maybe they are, and I am the last one to know....)

Paul
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  #3  
Old 09-15-2009, 07:51 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by Ironflight View Post
Where's your breather exhaust now Bill? Van's recommendation (at least I think it's their recommendation - most every RV I have seen with a breather pipe does it...) is to end it just ABOVE the exhaust, so that the burped oil (at least some f it) burns off on the outside of the pipe.

Running it in to the exhaust itself? Hmmm....I'd have to see quite a few folks who'd done that first before I'd be convinced it was a good idea (yeah, I'm pretty cautious). Not knowing the pressure in the exhaust pipe, I'd not know if I was pumping hot gas into the engine, or siphoning oil out.

Look at it this way - If it was an easy cure-all for belly oil, everybody would already be doing it, wouldn't they? (Maybe they are, and I am the last one to know....)

Paul
Paul,

Currently my breather tube is hanging on the engine mount and the exhaust is on the engine, which is sitting on the floor. (The exhaust is so bent, I couldn't get to the nuts to remove it.)

Not to be too much of a smart-aleck, my breather was positioned above the left exhaust stack as recommended. I just had to do it slightly different due to the location of the breather being on the front of the O-290 and the routing of the breather line under the left cylinders.

I'm with you regarding your caution, thus my post.
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  #4  
Old 09-15-2009, 08:12 PM
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rv9av8tr rv9av8tr is offline
 
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IMHO, I have to agree with Paul.... I think there is significant risk of pressure pulsing back into crankcase via the breather line.... and hard to predict oil sump behavior as a result. Besides, dribbling a flammable liquid into a 1,000 deg gas chamber..... sounds like something out of "Murphy's Law".....
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  #5  
Old 09-15-2009, 08:19 PM
cyrilmclavin cyrilmclavin is offline
 
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Default breather line to exhaust

Hi guys a friend of mine David Windmiller has an Edge and his oil breather line is plumbed into his tuned 6 into 1 exhaust. The placement of the fitting took some time to work out as it had to be tuned to the exhaust also, he says that he gets extra h.p. as the pistons have decreased air pressure against them going down therefore more torque more power.

cyril
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  #6  
Old 09-15-2009, 08:24 PM
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rocketbob rocketbob is offline
 
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Tom Martin did some testing a few years ago with a manometer, and found that pointing the breather to the exhaust is far less effective than it is to route the breather several inches behind the cowl exit. I have friends who have tubes welded into their exhaust which works fine - Bernoulli's principle applies here since the exhaust flow is a low pressure area. Some breathers I've seen have a 3/4" PCV valve plumbed in to prevent a backfire from blowing out the nose seal; but I think that would be highly improbable with the Vetterman exhaust. I have a wet vacuum pump sucking on the breather in my RV, drawing 8" Hg. on the crankcase, and it works great in reducing oil consumption, and more importantly, gives a few HP since reducing crankcase pressures reduces "windage" in the engine, which the engine normally has to work against. I've got a bypass check valve in place in case the coupling on the vacuum pump shears. 8" Hg. was the limit I found before the fuel pump would quit pumping, since its vented to the crankcase. Without a relief valve the pump can draw about 15" Hg. on the crankcase. I have approximately 300 hours with this setup, with zero problems.

Oil consumption is generally determined within the first three minutes of breakin. Unfortunately I did not break my motor in, but the 540 I overhauled last winter uses nearly no oil and stays crystal clear for a bit over 30 hours. Broke it in per ECI's instructions.
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  #7  
Old 09-16-2009, 07:17 AM
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I have welded a port into a collector, connected a gauge, and noted significant vacuum with no system additions. The best case evacuator includes a catch can containing a large area reed valve, which acts like a diode for the pipe pressure wave variations. Never installed such a system on Lycoming, but I ran 'em on racebikes years ago and they worked very well.
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  #8  
Old 09-16-2009, 07:54 AM
Steve Sampson Steve Sampson is offline
 
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Quote:
Originally Posted by cyrilmclavin View Post
Hi guys a friend of mine ....also, he says that he gets extra h.p. as the pistons have decreased air pressure against them going down therefore more torque more power.

cyril
Surely the decreased air pressure going down would be nicely balanced by the increased suction going up!
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  #9  
Old 09-16-2009, 08:38 AM
mahlon_r mahlon_r is offline
 
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Having a negative pressure working on the crankcase breather may cause excessive venting of normal crankcase oil vapors and may also have a effect on the fuel pressure that the engine driven pump delivers, if you are using a diaphragm type pump.
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  #10  
Old 09-16-2009, 08:53 AM
pvans pvans is offline
 
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I find it hard to believe there is any HP gain to be achieved by reducing the air pressure inside the crankcase.

First off, as one piston goes up another goes down so the volume inside the crankcase does not change. There is no air being compressed. The crankshaft does spin around in there , and it is a draggy thing, but the energy used up in spinning that around has to be minuscule.

Second, the pressure would drop naturally with altitude anyway. If the fuel pump is the limiting factor, why does it continue to pump at say 18,000 feet where the pressure is half of standard atmosphere?

Third, spinning the extra vacuum pump around burns energy too.

I think one could do better by installing those magnets that align the fuel molecules prior to combustion for better efficiency!
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