Topic: Airbox out?pods in......Where to w the breather tube...?

[dergs713]

Switched to pod filters for my 75 550. Anyone have any ideas what to do with the breather tube the comes from the top of the head and goes into the stock airbox..?
Matt

[domer]

buy a longer hose and run it so it exits below the bike, probably around where your battery breather is... Have fun! they can be a pain in the ass!!!

[TwoTired]

No, no, if you defeat the stock engine breather/filter, the hose should be routed up near or above the speedometer/tach, so you get the same benefits of air quality as the rest of the population.




Only half joking.     

[scottly]

Only half joking.     

Ha. Only half laughing...

[TwoTired]

Only half joking.     

Ha. Only half laughing...

The other half choking?
 

Having had a lung disorder, I don't take simple breathing for granted anymore.  It just isn't optional, for those endeared with consciousness.

Cheers,

[vames]

No, no, if you defeat the stock engine breather/filter, the hose should be routed up near or above the speedometer/tach, so you get the same benefits of air quality as the rest of the population.

I've seen you make this argument before. Does the volume of gasses coming out the breather even compare to the gasses coming out of an otherwise well-running engine (in terms of CO2, CO, hydrocarbons, particulates)? My instinct tells me it would be negligible and thus have no significant impact on the overall air quality impact of a motorcycle. But I really don't know the answer.

[65Ch3v3LL3]

I don't know how much emissions are there but wouldn't it be better to install a small breather on the head?

[cb550fcafe]

Any chance you have the stock rubbers between the air box and carbs you'd be willing to sell?

[KingCustomCycles.com]

A slight rise in the tube before dropping it to the swingarm area will act as an air/oil separater and help drain some of the condensed oil vapor back into the engine.  The water (steam) will exit as it should. 

[strynboen]

have only at tube on its only water,,  komes aut...just run the tube dovn at svingarm..but in one side..if some oil steam hit the wheel..but think not  a problem

[cameron]

1: get a mini-filter and put it on that breather.
2: drill and epoxy an inlet into one of your pods (I use #2) and re route the breather INTO it.

[strynboen]

think that ruin your cab syncro..

[phil71]

doesn't matter what you do with it as long as you keep it handy for the inevitable re-installation of the stock airbox.

[TwoTired]

No, no, if you defeat the stock engine breather/filter, the hose should be routed up near or above the speedometer/tach, so you get the same benefits of air quality as the rest of the population.

I've seen you make this argument before. Does the volume of gasses coming out the breather even compare to the gasses coming out of an otherwise well-running engine (in terms of CO2, CO, hydrocarbons, particulates)? My instinct tells me it would be negligible and thus have no significant impact on the overall air quality impact of a motorcycle. But I really don't know the answer.

The engine breather emits about 10-20% of the pollutants from an I.C. engine.  The variation stems from the condition of the piston/ring/cylinder fit, and the pressure differential between the combustion chamber and the crankcase chamber.  This fit varies with the temperature of the engine (which is unregulated in the SOHC4 air cooled engine). Anything that leaks past the rings goes into the crankcase.  Some of the combustion contents contaminates the oil supply and the rest exits the breather tube.  Although pure water does condense inside the engine and the breather tube, it is contaminated before exit by both the contents of the blow by gasses and the oil vapor hydrocarbons, almost all of it unburned.  If you think the water that drips out the breather tube is simply water, then I invite you to taste it.   I assure you the taste is NOT that of pure water.

The Hydrocarbons (burnt and unburnt), CO, NOx, and atomized droplets of oil, can easily be prevented from dripping on the ground and polluting the breathable atmosphere, by simply routing these vapors and gasses back to the engine to be re-burned.  This not only benefits breathing mammals on this planet, but the engine itself, though reduced contamination of the oil supply.  For the SOHC4, the slight vacuum applied to the crankcase serves to help the ring seal.  It's most definitely a win-win, to have it and a loss for everyone to defeat it.

Cheers,

[phil71]

What are you doing tasting that stuff?

[cameron]

think that ruin your cab syncro..

Thats why the #2!

[Gordon]

think that ruin your cab syncro..

Thats why the #2!

Even so, you're still running with a different air/fuel mixture in that cylinder.

[cameron]

the price I pay to reduce emissions.

[Danno]

if it is a 550 the honda service bulletin said reroute the hose down behind the motor and take it off the air box none the less keep it handy for when you decide you have had enough intake noise and crappy performance

these carbs require consistent unturbulent air and you can't get that with pods

[TwoTired]

if it is a 550 the honda service bulletin said reroute the hose down behind the motor and take it off the air box

That was for the 76 model.  However, both the 77 and 78 models had the hoses hooked up to the breather in the air filter box.

I haven't seen it, but I suspect the SB was either rescinded or superceded, particularly after the EPA noticed the engine vapors vented direct to atmosphere.

Cheers,

[Johnny5]

Here's what I did. I found a small breather at Autozone and fitted the hose from the back of the valve cover to the breather. Then built a bracket to mount it. It seems to be doing a fine job.

[lucky]

To be correct about it,  just run a hose to the back of one of the pod filters.
Drill a hole in the pod filter backing plate and put in a brass barbed hose fitting. Then the gases coming out will get reburned.

[scottly]

For the SOHC4, the slight vacuum applied to the crankcase serves to help the ring seal. 

Cheers,

Have you ever measured this "slight vacuum"? If so, please post your measured data.

[TwoTired]

For the SOHC4, the slight vacuum applied to the crankcase serves to help the ring seal. 

Cheers,

Have you ever measured this "slight vacuum"? If so, please post your measured data.

Nope, never measured.  But, the physics say there must be, unless the piston blowby is really severe, of course.
Do you know how a drinking straw works?  Same principle.

Cheers,

[scottly]

Measure how much vacuum is developed in the breather hose. This is NOT a PVC system, as used on cars, that tap into the high-vacuum intake manifold.

[Gordon]

Measure how much vacuum is developed in the breather hose. This is NOT a PVC system, as used on cars, that tap into the high-vacuum intake manifold.

I have to admit this is an interesting sub-topic to the "where should the breather line go" question.  There's no doubt that the take-off from the air box does proved some amount of vacuum to the crankcase breather, but how much vacuum does it provide and how much does it take to make a noticeable change in the seal of the rings?   

[scottly]

There's no doubt that the take-off from the air box does proved some amount of vacuum to the crankcase breather

Yes, there is doubt. Until someone taps an accurate vacuum gauge into the breather tube and proves otherwise, I contend that no measurable vacuum exists at that point on an SOHC.

[Gordon]

There's no doubt that the take-off from the air box does proved some amount of vacuum to the crankcase breather

Yes, there is doubt. Until someone taps an accurate vacuum gauge into the breather tube and proves otherwise, I contend that no measurable vacuum exists at that point on an SOHC.

I don't see how there could be a doubt.  The cylinders create a vacuum in order to pull in air and fuel.  If you have any opening in the intake system, vacuum will exist at that opening.  The port in the air box that's meant to be connected to the crankcase breather is an opening in the intake system, so there must be a vacuum at it. 

[scottly]

Nope. The breather tube ends in the air box, on the atmospheric pressure side of the carbs. Don't take my word for it, measure it yourself.

[Gordon]

Nope. The breather tube ends in the air box, on the atmospheric pressure side of the carbs. Don't take my word for it, measure it yourself.

I don't have to measure it to know that there's a vacuum on the back side of the carbs.  If there weren't, how would air get sucked into the carbs through the air filter, through the carbs, and into the cylinders?  The carbs do not supply the vacuum, they only regulate it. 

I'm only trying to say that it's an interesting question to ask how much vacuum the breather port on the air box supplies, and how much vacuum it takes to provide a noticeable difference to the overall performance of the piston rings.  If this is going to be a discussion on whether or not there is actually a vacuum in the air intake of an internal combustion engine, then I'm going to respectfully remove myself from it, because I don't know what to say at that point. 

[TwoTired]

Nope. The breather tube ends in the air box, on the atmospheric pressure side of the carbs. Don't take my word for it, measure it yourself.

It is not atmospheric pressure until you get to the outside of the air box inlet port.
If it was atmospheric pressure in the air box, no air would move into it.  So, by definition what is inside the air box MUST be lower pressure (partial vacuum) than the outside atmospheric pressure.
In fact, all along the path from air inlet to intake valve is a gradient pressure drop.  It is caused by the falling piston, and the negative pressure created by that expanding void is filled from the air inlet at the air box entrance.  All along that pathway a negative pressure exists, as that is the only reason for air movement in the duct work.  If you want air to move, there must be a high pressure moving toward low pressure, otherwise there is no movement.  The breather system in the SOHC4 is sources partial vacuum at a point in the air path after the air filter. The filter membrane creates another pressure drop across it.  The inlet air opening provides another point at which a pressure drop occurs.  Both of these points, as well as the duct distance and wall boundary layer, creates an additive pressure differential that absolutely must be less pressure than atmospheric.  It is certainly measurable with proper equipment.

Measure how much vacuum is developed in the breather hose. This is NOT a PVC system, as used on cars, that tap into the high-vacuum intake manifold.

PVC stands for Positive Crankcase Ventilation.  Which, as you pointed out, is NOT what the SOHC4 has.  Auto PVC systems have both and inlet and and outlet the crankcase so air can flow through it.  The SOHC4 has a single port.  (It can employ this because the internal crankcase volume of the engine doesn't have a net change due to two pistons moving while the other two move down.)   So, if you apply even a small negative pressure it will stay inside until equalized from another source, most probably blowby, which would then be fed to the engine combustion chamber through the carbs.

There are many flow meters that use the pressure drop across a calibrated distance in order to determine flow rate.  No pressure drop equals no flow. This is a basic principle of fluid and flow dynamics being exploited to gain measurable information.

I admit I never measured the breather tube pressure, or the crankcase pressure, for that matter.  Some things you know exist, simply because they must obey the laws of physics.  I don't have to measure the weight of all things to know that if they have mass, they will be drawn to the earth.

The negative pressure can also help keep engine leaky seals from oozing oil outside, btw.

Cheers,

[cameron]

just for posterity:

[jonboycox]

While I am certainly no expert, it would seem a better option to separate the line into four and then do the air pod modification to all four pods. That would ensure that no one cylinder was being treated differently, as well as theoretically give you the same pressure draw as the air box set up.

[scottly]

I'm only trying to say that it's an interesting question to ask how much vacuum the breather port on the air box supplies, and how much vacuum it takes to provide a noticeable difference to the overall performance of the piston rings.

I found this in a magazine article about a 900+HP big-block Chevy:

The primary function of a beltdriven vacuum pump is to stabilize the piston rings so there is only pressure on one side of the compression ring, as well as to reduce crankcase windage for better oil control (more power). The vacuum pump creates an atmosphere inside the crankcase ranging anywhere from 13 to 15 inches of vacuum on a wet sump (higher on dry-sump systems) and literally sucks out any blow-by inside the crankcase to promote a better ring-to-cylinder-wall seal. Conventional engines that don't utilize a vacuum pump generally have pressure on both sides of the rings, which not only hinders the ability of the rings to seal against the cylinder wall, but also poses resistance to descending pistons, robbing more power. It's important to note that while many applications can benefit from a vacuum pump, it's best suited to attempting to extract every last bit of power, and can be worth up to 20 additional ponies.

[cameron]

Im also no expert. A friend of mine came up with that idea.
He IS an expert, however, and the plugs chop even.
Sync is good, we just had to mix-adjust a little to make up for the blowback. IIIRC, it was literally like a 16th of a turn.
Splitting to all 4 would be perfect, but more trouble than its worth, IMO!