Crankcase breather and air box test on dyno

[koko64]

Did some dyno tests with various air box, jetting and crankcase breather combinations.

Found no difference in power between running breather hose from oil seperator box to the air box and to the atmosphere. I suppose the bike runs at lower revs than the racers at 9000 rpm max. Also the actual air box is smaller and the racers run the big breather cavity.

Curiously, I noticed two things; the idle mixture was leaner with the breather hose detached from the air box and vented to the atmosphere. It was leaner by about .4 to .5 with the EGA. It was richer with the stock breather vented to the air box. I turned out the IMS a quarter turn and it was still leaner with the breather detached. Weird.

The other curious thing was that the oil level glass ran much cleaner with little if any mist or vapour when the breather was vented to the air, even on short rides in the winter to and from the dyno and on local street testing of jetting.

For the record, my M900 has the stock breather valve and oil seperator box under the seat. I normally run the stock breather set up with the breather hose to the air box. I removed the hose and blanked off the hole in the air box. I let the oil seperator box breathe to the atmosphere. It certainly is tidier under the tank now and the cable to the FCRs is free of the breather hose crowding it.

[DarkStaR]

Nice.  Good info. 

Well there it is, we can all squash that arguement... 

[koko64]

Actually, it makes sense to use some intake vacuum assistance to vent the crankcase and to have the crankcase vented to other large cavities like breather boxes and air boxes. There are horsepower gains to be had by reducing pumping losses in a high revving V twin. The factory racers have this set up for a reason.

It's just that my old two valve 900 only revs to 9000 rpms.

[battlecry]

Was the airbox hole for the hose plugged when it ran leaner?  Maybe there was an air leak.

[ungeheuer]

Hmm.. some interesting stuff Tony. 

[ducatiz]

For the record, my M900 has the stock breather valve and oil seperator box under the seat. I normally run the stock breather set up with the breather hose to the air box. I removed the hose and blanked off the hole in the air box. I let the oil seperator box breathe to the atmosphere. It certainly is tidier under the tank now and the cable to the FCRs is free of the breather hose crowding it.

So you just removed the hose from the separator to the airbox?

[koko64]

Yeah, I just removed it and plugged the hole to the air box. I used a plastic plug and gooped it as well. No air leak from there!
A buddy has done the same but runs a little K&N filter off the seperator box. I'm not running anything at present off the seperator box except for a 2 1/2 inch curved hose so the hole isn't facing forward. I dunno, didn't feel right to have it facing forward.

[koko64]

Just had a thought, if I look at the dyno run/EGA charts, and if I try real hard, I can almost interpret the data to support the stock breather set up giving more power than venting to the atmosphere. Bugger! I wanted that hypothesis to win so bad!
But when I look at the charts, the results appear to be related to changes to velocity stacks and jetting. In other words; air and fuel.

[ducatiz]

Just had a thought, if I look at the dyno run/EGA charts, and if I try real hard, I can almost interpret the data to support the stock breather set up giving more power than venting to the atmosphere. Bugger! I wanted that hypothesis to win so bad!
But when I look at the charts, the results appear to be related to changes to velocity stacks and jetting. In other words; air and fuel.

the effect is probably very small at lower RPMS and increases geometrically after some point.  the amount of vacuum has to overcome the amount of pressure generated in the crankcase first, which of course is increasing as the piston speed is increasing.

[He Man]

the point of the crankcase breather box for standard vehicles was emissions not power wasn't it?

[ducatiz]

the point of the crankcase breather box for standard vehicles was emissions not power wasn't it?

yes BUT it was in use on racetracks long before...

[koko64]

There's nothing to say the stock breather system wouldn't yield net gains with motor with different mods like bigger capacity or higher compression. The principle has been proven on the track.
That said, the dyno tuner who specializes in 4 cylinder racers said that he runs all the breathers ln customer race bikes to the atmosphere via a catch bottle or tank.  Said he has never seen a loss in hp from this. He does this as a matter of course as a race mod.
Any thoughts on this?

[koko64]

I'll probably put the breather hose back on, just in case there are any gains to be had that we couldn't detect with the testing methodology.
It's just the foggy oil level sight glass and ridiculously tight fit with the carb cable annoys the shit out of me. Also, is warm slightly oil vapour polluted air affecting Idle mixture readings? Many people see such a system as creating potential air/fuel charge contamination and stress the requirement for clean, cool air in the intake charge for engine efficiency.

I even drilled a hole in the back of the air box to fit a hose away from the carb cables but I decided I didn't like the 'forward' facing location in case there was an issue regarding air flow direction at higher speeds affecting efficient evacuation of crankcase gasses.  So I have plugged that hole at present. It was at the back of the box above the left carb and the hose ran over my small battery. The hole faced forward which messed with my head because the filter angle faced it. The stock position flows across the air box.

It appears from a great link on this sight (thanks but I forget who put it up), that BCM and John Nichols are of the opinion that the stock venting system is the best if you can't run the Racing system (like on a Monster). They appear to hold that the gains from the crankcase ventilation may outway the losses from the air charge contamination.

I only have so much R&D cash to burn, so if anyone has data besides mine it would be appreciated.

Yeah, I have given this issue way too much time, thought and effort.
 

[koko64]

In conclusion , I suggest staying with the stock breather system. If you want to vent to the air, do it from the oil seperator box with a filter that flows very well.
The oil seperator box gives additional crankcase breathing volume, with the addition of the air box even more so. The connection to the air box gives additional vacuum assistance to crankcase venting.

I have no doubt that sustained higher revs like at a track day is the environment where the greatest gains would be made from the stock or race systems (duh). Running a little filter directly from the breather loses the oil seperator box volume and function. Id like to see someone test the stock system against a filter off the breather with no oil seperator box. Where would your money be?

Moisture from the donk in the very cold, or on shorter runs escapes easier with venting to the air and doesn't as easily drain back through the valve back to the crankcase.

I am disturbed by the EGA reading at idle being a little higher with the breather going into the air box. This even after I richened the IMS.

Those of us with FCRs and want to run the stock breather system will need to adjust the cable enough to  give adequate clearance for the breather hose. A custom cable may help, or running a filter off the seperator box.

Relocating the the entry of the breather hose to the air box is best left to those who know what they are doing. I didn't..

It stands to reason that there is a more obvious performance margin between running the seperator box and going straight from the crankcase breather to the air.
Someone else can test that..

Cheers

[ducpainter]

It isn't surprising, to me any way, that it ran leaner with the breather disconnected.

Think about all the oil mist and combustion gasses in that breather set up that would raise HC's.

It's not unlike the early EGR set ups on cars...

except they ran like crap with and without the EGR hooked up.