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Plumbing oil breather line to the exhaust?

N941WR

Legacy Member
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.)
 
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
 
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.
 
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".....
 
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
 
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.
 
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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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!
 
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.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
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!
 
I find it hard to believe there is any HP gain to be achieved by reducing the air pressure inside the crankcase.

Here is why it helps:
Blowby gasses are corrosive, and contain water vapor. When the crankcase is pressurized even a little bit, rings tend to float and lose their seal at the bottom of the stroke. Hot rodders use various means of crankcase evacuation (header ports being one) to reduce the crankcase pressure caused from blowby. Street cars use the PCV valve to accomplish the same thing. In addition to improving ring seal, the positive removal of blowby gasses decreases oil contamination, and thus improves oil life.

The reason that PCV valves wouldn't be useful for a lycoming is the same as hot rodders: high power output equals high manifold pressure equals little to no intake vacuum, no vacuum equals useless pcv valve.

Given the rpm range, I doubt that a lycoming would pick up a bunch of power from a good crankcase evac system, but it might stay cleaner (inside and out) longer. :cool:
 
I have a hard time believing more people haven't seen this, I've seen this trick on experimental aircraft for years. My airplane is not set up this way, but I've seen many (ok maybe they're older) RV's with this mod and I'm not aware of any problems. I recognize that's a pot full of anecdotes.

My main concern would arise around the scenario where you welded a fitting to the pipe and the weld later cracked and broke out (for whatever reason)... you might not like the results.

I'd have a talk with Mr. Exhaust System Vetterman if I was considering it.
 
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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.

Its been dyno'ed on a 540, 7hp gain, 3/4hp to drive the vacuum pump. This is on a system like mine, obviously the gain is not as much when venting to the exhaust. As the vacuum increases, less horsepower is required to drive the pump, just as your vacuum cleaner will go up in RPM when you hold your hand over the end of the hose.

Oil vapor is reduced since there are fewer air molecules in the crankcase to carry the vapor away. It does indeed work. I've been told that it also decreases piston ring flutter.

A good explanation here:
http://nutterracingengines.com/racing_oil_pumps/crankcase_vacuum_facts.html
 
Unfortunately, I must report that it was a bad idea to plumb my oil breather into my exhaust. It resulted in a dramatic increase in oil consumption...over a quart an hour. I used AN8 flex line directly from the breather, through an AN8 free-flow check valve, into a 3/8"NPT bung welded perpendicular into the exhaust about 8 inches before the tip (just in front of the firewall). As it made no sense that this was the cause of my oil consumption, I extensively troubleshot elsewhere. I was worried that I had excessive blow-by the rings, even though the exhaust pipes were dry (including the one with the breather).

I finally disconnected the exhaust outlet and routed the breather into a simple catch can. After 2+ hours I’d hardly put any oil in the catch can, and had consumed very little oil. I thought that maybe I was pulling too much vacuum on the engine breather and evacuating oil mist that would normally settle in the engine.

I decided to check crankcase pressure, with surprising results. I referenced the Continental Service Bulletin M89-9 which describes using an airspeed indicator as a pressure instrument. I found a free 3D printed Lycoming dipstick cap adapter here:

Lycoming Oil Dipstick Adapter

I sealed the 3D printed adapter, tapped out the hole to 1/8" NPT, and installed a nyloflow 1/4" line routed into the cockpit and attached to the airspeed indicator.

With the breather completely open, my crankcase pressures were typically 70 mph (90 max on the Continental big bore engines) until I got above 2500 rpm where the pressure peaked at about 100 mph. Normal results and I expected them to be less when I re-attached the exhuast outlet.

With the breather plumbed into the exhaust, the crankcase pressures INCREASED by nearly double! At full power I was showing over 165 mph. Somehow, instead of the high flow exhaust creating low pressure, the exhaust was pressurizing the crankcase. I can’t explain it.

So, in my case, it was a good experiment with bad results.
 
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Besides, dribbling a flammable liquid into a 1,000 deg gas chamber..... sounds like something out of "Murphy's Law".....

It sounds more like one is making an afterburner. If you angled the exhaust tubes in the right direction, or maybe added some servos for thrust vectoring...
 
An angled tube welded into the exhaust pipe, at the right angle, and with the tip properly shaped and vectored, has been used in the EZ community for at least 35 years - literally hundreds of EZ's. A high tech :D female NPT threaded NAPA PCV valve is mounted on the tube welded into the exhaust header. I have almost 5,000 hours of trouble free flight hours with this system ...BUT.. you need to do it right or you may have trouble.

Right means you will need to experiment with the entry angle, where the breather bung exits in the exhaust stream, etc, etc - and instrumentation with a forced air source (I used a Shop Vac on steroids) to determine the right location, penetration depth, angles, etc.

I'll see if I have a picture somewhere.
 
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With the breather plumbed into the exhaust, the crankcase pressures INCREASED by nearly double!

Jimmy, you're definitely doing something wrong. I've been measuring pressure reduction with various case evacuator systems for quite a while. First one was in 1985.

Got an installed photo of the "AN8 free flow check valve"? I've built systems with reed valves for high RPM, but like Dick, I just use an ordinary NAPA 229000 check valve on a Lycoming.
 
Alan Nemo (AntiSplat) has a solution. I put this on my RV4:

147FA526-967E-4466-BBF0-8C549AE61322.jpg

It ended any oil on my belly. It was a pretty leak free engine, but any small dribble ended too. There is a T shaped check valve that vents overboard through the blue line in the event the pipe going into the exhaust becomes plugged (cokes). You need to check that once in a while and clean out any coking that might be present. My oil consumption was about 15 hours per quart before installation and that hasn’t changed. I bought one for the RV6 I’m building too.
 
AN8 check cracking pressure?

While it could be the angle entry into the exhaust, DanH is hinting that the opening pressure and internal resistance of the check valve might be a factor.

I wanted a check valve for 1-2-3- in-H2O cracking and flow resistance . . . it was hard to find one that low. Note: different application, not the breather-to-exhaust.

Unfortunately the racing world is about shiny & horsepower, but not so good on publishing technical performance information on components.

Edit: Thanks to eek for the note below. Quantifying the NAPA style is good, and the very reason for it's design. Most inline checks are spiral spring and ball designs with higher opening pressure. While it is not impossible to remain coke free, it certainly is rare and no one should leave off the pressure relief valve scheme borne from some failures and a long thread on VAF some years ago.
 
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While it could be the angle entry into the exhaust, DanH is hinting that the opening pressure and internal resistance of the check valve might be a factor.

I wanted a check valve for 1-2-3- in-H2O cracking and flow resistance . . . it was hard to find one that low.

Unfortunately the racing world is about shiny & horsepower, but not so good on publishing technical performance information on components.

Delta P across a new NAPA check valve at 40-220+ cfm is less than .1" water. My experience is the success of dumping the crankcase breather is relative to the angle of entry relative to free stream exhaust, the oval shape of the bung's exit plane, the bias cut of the bung relative the the free stream velocity, and prevent coking up the bung via short distance from the exhaust port flange.
On one LongEZ with this system, over 3,300 hours, the bung never coked up. The NAPA valve was replaced once because they used to cost < $5, and I thought I could begin to detect some delta P across it after 2,500 hours

No more oil leaks, oil consumption remained at 10-12 hours /qt, and it produced more HP since it was faster. The naturally aspirated and carbureted O-320-D3G took my Long to well over FL310, and the standard Lycoming mechanical fuel pump worked fine up high. The first person I know who was doing this and selling crankcase vent exhaust kits was Wes Gardner from Chino who developed this for his O-320 Varieze in 1982. Wes (RIP) was an avid car and boat racer.

Maybe Wes had an O-290 - too many years and beers ago.

Not RV related? Okay, I met Alan Tolle at the Wright Bros Invitational in 1984. I'd never seen a RV-4, so we both removed our cowlings for the Judges...and his crankcase vent into the exhaust was very similar to mine. 1984 guys; this isn't something new and unproven.
 
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Yes, Jimmy may have a valve with some resistance to opening.

The tailpipe installation isn't optimal. It depends on flow velocity rather than pressure variation, and the resulting negative pressure value can vary quite a bit depending on tube end shape, insertion depth, and insertion angle.

I did a simple experiment some years ago, playing with tap tube angles and insertion, in a tube attached to a big blower running wide open. Short summary below. Note the variation. It was a not comprehensive test, but enough to illustrate the problem

Returning to pressure, although there is some pressure variation in the tailpipe, wave action from multiple cylinders can overlap each other. A crossover 4-cyl would be least affected, while a 6-into-1 would need to rely solely on velocity. The well known Sky Dynamics center-of-the-collector approach is a good example.

I, Dick, and others prefer tapping a headpipe relatively near a single cylinder, where pressure is very highly negative and positive. Take a look at the relevant CAFE report for example wave pressures. The headpipe check valve captures the high negative and rejects the positive, the result usually being more breather suction than the tailpipe variety. I measure about 3.5" Hg (note, not H2O) with a tap 11" from the cylinder flange. Next time I'll locate it closer to the flange.

BTW, if the goal is merely reduction of oil mess, it's possible to tap the breather to the tailpipe with no check valve at all. Standard practice on TAT Cirrus installations, and some Mooney models. Tap cleaning intervals are 50 and 100 hours respectively.
 

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My three cents worth

I cheated and welded a Stainless steel pipe on the 45 degree angle directly into a tail pipe with only a 1/8" lead sticking into the exhaust pipe. Used the check valve for back flow.
I believe a perpendicular attachment of the pipe port is not a good thing, It needs an angle. But maybe I'm all wrong.
My 550 hour 0-360 channel chrome cylinders with SDS injection and ignition, Vetterman crossover exhaust, always burns a quart in 6 hours with a slightly messy belly.
After the mod most of the messy belly went away and the oil consumption stayed the same. I must have a small oil leak I do not seem to be able find.
I see no downside to the mod except I expect to be cleaning the port once in a while.
I do not expect the engine to suddenly explode because of ????
My three cents worth Art
 
I see no downside to the mod except I expect to be cleaning the port once in a while. I do not expect the engine to suddenly explode because of ????

Definitely tee a second check valve into the breather line, at least until you can determine the rate of coke buildup in the exhaust tap. Some AntiSplat installs on the RV10 tailpipe have gone as little as 35 hours before coking shut.

The second valve ensures there can never be positive case pressure. No fun if you pop a nose seal. Recall the good book, specifically Compressions 8.7:1 ;)
 
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I have the AntiSplat exhaust setup and clean mine every oil change at 50 hours. I have a reasonable amount of coking in it each time. It's never closed completely, but I wouldn't want to push it to 100 hours or forget about it all together. Very clean belly. I like the setup.
 
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