Crankcase breather

[Jacobien]

Hi,

Recently spoke to a friend who said that the crankcase breather pipe from the crank to the airbox is only due to emissions controls.

He said that in racing they remove it cos it heats up the air in the airbox and it adds oil vapor to the intake.

True or false?

(No cash prize)

 

[RJ2112]

I can't answer if they remove it for racing.... but it is there for emissions control, and it does route oil vapor into the intake.

I can't think the heating is going to be enough to matter.... the source of crank case pressure is the blow by from the rings, and it SHOULD be a very small volume in comparison to what is supposed to stay inside the compression chambers. I'd guess something like less than 1%?

In racing the idea is to prevent slippery stuff from spilling onto the track. That would make it seem unlikely that this particular smog control would be removed.... it would not surprise me if it were done anyway.

 

[deeptekkie]

What RJ2112 said plus it is not only blowby, it also caused by the pressure within the sealed crankcase as the pistons rise and fall, (sort of like the crankcase itself being a compressor). There is a huge and constant surge of pressure caused by the pistons and this pressure has to go somewhere. In olden days it was just vented to the atmosphere but since it contains hot oil smoke and blowby from each cylinder, (especially those with higher compression = ours), it now must be recirculated through the engine for additional burning. I would think that for racing it is vented to the atmosphere so the engine is getting cleaner, cooler air without oil vapors.

 

[thieu]

It can be a source of increased horsepower and increased fuel economy in some applications as well. Pulling a vacuum in the crankcase means the the pistons have less air the shove out of the way as they move back down the cylinder. :thumbup: so you go faster!

 

[opnwhlmnd]

Hi,

Recently spoke to a friend who said that the crankcase breather pipe from the crank to the airbox is only due to emissions controls.

He said that in racing they remove it cos it heats up the air in the airbox and it adds oil vapor to the intake.

True or false?

(No cash prize)

TRUE

You can unhook it from the airbox and install a small K&N type filter and vent it to outside.

I have mine done that way.

Ring blow by on a new engine with conventional style rings with a gap like the FZ has will have around 7% blow by when new and go up from there. Total Seal gapless rings reduce blow by to around 2%. There is more blow by in our engines than you would think.

So yes you are introducing hot oil vapor and heat to your airbox with it hooked up. Not a giant hp gain but every little bit helps.

.

 

[champion221elite]

Are synthetic oils more resistant to vaporizing than dino oil? Or is the vaporization more related to compression forces rather than heat?

 

[opnwhlmnd]

Are synthetic oils more resistant to vaporizing than dino oil? Or is the vaporization more related to compression forces rather than heat?

Vaporization is related to the flash point specs of the type of oil you use and the amount of breakdown over the life of the oil change.

The flash point temp is the point the oil can vaporize.

Should use oil with a 400 degree or higher flash point. The higher the number the more heat it can handle before reaching the flash point.

Oil in the engine becomes saturated with fuel from the ring blow by over time and lowers the flash point. Synthetic oils do a much better job of not breaking down from the fuel mixture.

.

 

[RJ2112]

TRUE

You can unhook it from the airbox and install a small K&N type filter and vent it to outside.

I have mine done that way.

Ring blow by on a new engine with conventional style rings with a gap like the FZ has will have around 7% blow by when new and go up from there. Total Seal gapless rings reduce blow by to around 2%. There is more blow by in our engines than you would think.

So yes you are introducing hot oil vapor and heat to your airbox with it hooked up. Not a giant hp gain but every little bit helps.

.

Could you point me at a source that I can read up on percentage of blow by? Not trying to sound like a d!ck, I just can't believe 7% and getting worse over the life of the engine from new. How is this being measured?

 

[opnwhlmnd]

Could you point me at a source that I can read up on percentage of blow by? Not trying to sound like a d!ck, I just can't believe 7% and getting worse over the life of the engine from new. How is this being measured?

Do a leakdown test on your engine and see for yourself. Not a perfect way but cheapest tool wise.

I've built over a hundred racing engines in my life. And I'm not talking about just putting an engine together. All the machine work that goes with it also. With Total Seal or any gapless ring we like to see 2%. With conventional gap rings we are happy with 7%. You cannot have a perfect seal and zero blow by with a metal cylinder and metal rings going up and down the cylinder. There will always be leakage past the two metal surfaces.

There's my source, experience and knowhow. :Flip:

.

 

[RJ2112]

Do a leakdown test on your engine and see for yourself. Not a perfect way but cheapest tool wise.

I've built over a hundred racing engines in my life. And I'm not talking about just putting an engine together. All the machine work that goes with it also. With Total Seal or any gapless ring we like to see 2%. With conventional gap rings we are happy with 7%. You cannot have a perfect seal and zero blow by with a metal cylinder and metal rings going up and down the cylinder. There will always be leakage past the two metal surfaces.

There's my source, experience and knowhow. :Flip:

.

So you're talking cold metal and cold cylinders. I can follow that. Would you agree, that once an engine starts that the rings expand? As they have much less mass than either the piston or the cylinder wall, they expand fastest and furthest?

Isn't that why standard rings have an end gap? Don't the 2 or 3 rings in most designs further reduce that leakage, especially as the gaps are supposed to be offset?

I've been led to understand that almost all blow by occurs before the engine warms up.... obviously, there's still a relatively slight amount when everything's up to operating temps. There is still a gap between the ring ends, however slight.

The fluttering of the rings as the piston changes direction and deals with the combustion pressure change are going to alter their sealing characteristics as well.

If an FZ6 engine lost 7% of the cold air charge into the crank case on each cylinder with every combustion cycle, that would mean every crank rotation would 'dump' 21cc of fuel/air into the cases (two cylinders). Multiply that by whatever RPM you're running, and you get to many liters per minute. Idle @ 1500 RPM X 21cc = 31,500cc... 31,500/1000 = 31.5 liters.

I find it hard to believe that the breather hose between the crank case and the air box is designed to handle that much flow. Especially when (if that ratio stays consistent) when you're at max RPM (North of 12K RPM) that volume goes to greater than 252 liters/minute.

I don't think you can get that much air through a 3/8" hose.....

 

[iSteve]

I may be wrong about this but having the breather attached to the airbox would seem to evacuate the crank gasses faster. The airbox has a lower pressure due to the air being sucked into the intake. Also as the rpm increase the pressure drops causing even more vacuum therefore sucking more crankcase gasses.

Also 7% seems high to me especially in a engine with ceramic coated cylinders and much tighter tolerances then a steel sleeved engine. I would also think that if 7% + blowby is happening you would want a higher crankcase pressure to help prevent blowby much like you have with back-pressure in exhaust pipes for exhaust gasses.

Whatever the case I'm sure the engineers at Yamaha have this all set for ideal compromise between performance and pollution control.

Of course on a track it's all about total performance so engine longevity, pollution control, low speed drivability are not a concern.

 

[FZ6-ZN]

On race bikes the crank breather & other overflow pipes are rerouted to a "puke bottle" to prevent any overflow spewing onto the track.

FZ6-ZN

 

[opnwhlmnd]

I went down to my mc dealer friend today and he let me check leakdown on an R6 with 560 miles on it.

It had 6.8% leakdown cold and 5.5% warm.

From my dyno experiences I would guess the 5.5% would drop to about 5% over 4000 rpms.

I have my crankcase vented to atmosphere and am happy with the results. True you may get a little vacuum help from venting to airbox but to me and most performance people it's not worth putting the extra heat and oil vapor into the fuel/air mixture. You go to great lengths to have cold air enter the airbox and then introduce 260-300 degree crankcase vapors to it. Hmmmmm.

Plus any day I can piss off an environmentalist it's a good day for me.

 

[McLovin]

I went down to my mc dealer friend today and he let me check leakdown on an R6 with 560 miles on it.

It had 6.8% leakdown cold and 5.5% warm.

From my dyno experiences I would guess the 5.5% would drop to about 5% over 4000 rpms.

I have my crankcase vented to atmosphere and am happy with the results. True you may get a little vacuum help from venting to airbox but to me and most performance people it's not worth putting the extra heat and oil vapor into the fuel/air mixture. You go to great lengths to have cold air enter the airbox and then introduce 260-300 degree crankcase vapors to it. Hmmmmm.

Plus any day I can piss off an environmentalist it's a good day for me.

Great info on this thread guys, thanks a bunch.

I have few questions on this topic and Im completely ignorant about this stuff so excuse me. Does this all mean that you are slowly losing oil this way over time? With the external collector bottle, how much oil accumulates over lets say, one good days ride? Is this loss significant enough to have to add some oil over time?

 

[novaks47]

I went down to my mc dealer friend today and he let me check leakdown on an R6 with 560 miles on it.

It had 6.8% leakdown cold and 5.5% warm.

From my dyno experiences I would guess the 5.5% would drop to about 5% over 4000 rpms.

I have my crankcase vented to atmosphere and am happy with the results. True you may get a little vacuum help from venting to airbox but to me and most performance people it's not worth putting the extra heat and oil vapor into the fuel/air mixture. You go to great lengths to have cold air enter the airbox and then introduce 260-300 degree crankcase vapors to it. Hmmmmm.

Plus any day I can piss off an environmentalist it's a good day for me.

Haha, same here. You say I have to have all this BS on my bought and paid for vehicles. Pffft, yeah right!

Some vehicles respond well to having the crankcase ventilate elsewhere, others see no gain, and some even a loss. On my '02 Protege, the thing ran like crap when I added a filter instead of the factory stuff. Idled rough, got worse mileage, and didn't seem to pull quite as hard. Very minor, but noticeable differences. I see it like this : either it will do nothing other than keep your intake/throttle body cleaner(worth it), or it will net you a small gain, or it will totally piss off the vehicle and make it run a tiny bit worse. I say try it, and see what happens. I may try it again on my car, only have it route to a catch can instead. Also keep in mind, over time the filter will get really wet with oil, and eventually drip all over everything, so you need to keep it cleaned(if your're venting via a filter).

 

[FinalImpact]

A couple things to consider:
An engine with higher blow by will also increase the tendency towards detonation. So if the crank breather is ported to the intake and there is lots of it, you also get more carbon, sludge, and deposits in the intake, exhaust and combustion chamber which increase detonation. But as stated, oil does not burn well and it by itself (oil vapor) lowers the flash point of the fuel charge resulting in detonation. hence the reason most race engines have multiple scavenge pumps to remove vapor from the heads, crankcase and oil tanks.

If your riding style is to lug the bike around, this results in extremely high loads on the piston and increases blow by too. . . . not to mention increased wear by the high loads!

 

[Nelly]

opcorn:opcorn:opcorn:opcorn:
What a brilliant thread, its the best one I have read in ages.
Great informative answers and great probing questions.

Nice one

Nelly:thumbup:

 

[Hellgate]

My R6 track bike is a former AMA pro Superstock bike, the crank vents to the airbox with no issues. For street bikes I see no reason to take emissions stuff off, there is too much crap in the air already.

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