Secondary Air System?

Great informative post Joel

You didn't bother to read the post but you'll try and quote a wiki to disprove it? Amazing.

Yes, filtered air from the airbox is injected to the exhaust to promote clean burning. In that sense, the F800GS HAS TRADITIONAL SAS :)

What is fairly high tech is that the air injection actually improves volumetric efficiency (good breathing) of the engine.

I couldn't explain in a 50X post all that goes into the volumetric efficiency of this engine because I'm good enough with math to recognize good math, usually, but not nearly good enough with math to explain it.

But as an exercise, think of air and exhaust having mass, which it does, and having compressibility, which it does, and tending to spring back when it compresses from banging into a closed valve, which it does.

Think of the induction, combustion chamber, and exhaust as a city street with red and green lights representing intake and exhaust valves.

Think of the cars having acceleration provided by the pumping of the piston as well as combustion.

Now if you add more lanes, the cars which represent the intake air and exhaust, will get to the red light of the intake valve quicker and come to a stop, at which point they will have to accelerate into the combustion chamber. Air has was and is compressable, acceleration takes time.

These are gross simplifications that I can just wrap my mind around.

When the leingth and size of the induction tract, lift, timing and angle of valves, leingth and restriction of exhaust, restriction of the filter, and IN THIS CASE, vacuum breaking properties of the SAS system are all tuned to work in harmony, it's like a 2 lane road where the lights are always green and moves better then a 4 lane with red lights.

You absolutely can increase peak power at red line through modding of intake, exhaust, filter, or even valve timing, but I believe it will always be at the cost of mid range torque.

If you priorities are peak power, mod away. If not, I don't beleave you can improve much on the factory design.

I'm not apposed to add on parts, we sell them :)

Will post pictures when time presents, but first, I have to take them :)

Nah, didn't try to disapprove it. Just didn't have time at the time to read through the whole thing to see if what was saying is in fact actually a secondary air injection system. You're reaching again digdesign.

I understand what you are saying and agree fully about the fact that there IS a secondary air injection system on these US F8's. And being a BMW employee, I appreciate your thorough explanation of how the secondary air injection system works on this bike. However, since many folks around here take every word you say as 'the gospel', and you have felt the need in the past to want to shrink me and speak condescendingly towards me, I'm not going to let a false opinion-based statement that you've said go unchecked. Especially since you and the gang have regularly flamed me in the past over and over for speaking opinion. I will correct you when need be if you want to play that game. And I am now.

As technically advanced as this engine may be, with its computer controlled air/fuel mixture and fuel injection, it is still a internal combustion engine, with a piston, intake valves, and exhaust valves. Humans have been improving HP across the RPM (with no 'mid-range reductions') on the internal combustion engines in motorcycles for decades by tuning air/fuel mixture and increasing EASE of intake flow and EASE of exhaust flow. Your above explanation to support your opinion is cool, but unfortunately needs to be corrected. When the intake valve lifts to let air/fuel mixture in, how hard does the downward motion of the piston need to pull in order to suck the appropriate amount of air in? In stock form, more. This is why there is less power in stock form. Because more of the piston's energy is expended to pull the air in through the intake valves. Now, with a higher flowing air filter and/or airbox mod, the air is much more easily drawn into the combustion chamber, with much less resistence. This means that more of the piston's energy can go the propelling the bike instead of pulling in air to operate. The same can be said for the exhaust valves. When they lift/open, how EASY or HARD is it for the exhaust fumes to exit the chamber? With an exhaust that is more restricted (stock), more of the upward motion/energy of the piston is expended on pushing the exhaust gases out of the chamber, instead of going towards the gearbox and drivetrain. With a higher flowing air filter and higher flowing exhaust, air/fuel are let into the combustion chamber more easily once the valves open. And when combusted, are expelled out of the exhaust valves much easier. When the engine's piston(s) don't have to use as much energy to pull in air/fuel mixture and expel exhaust gases, more of that piston's energy can go towards the drivetrain, which is why we see HP improvements across the RPM range when doing these mods, including the midrange. But as I said before, to reap the benefits of a higher flowing intake system and exhaust system, you MUST richen the AFR to match. And on this bike, it's manually through the use of electronics: Booster Plug or Accelerator Module doing it through a plug-and-play fixed 6% enrichment across the board, or a Power Commander allowing to make custom maps and load them on to the ECU which more tweaky.

One correction, the goal in the scenario you describe is not to richen the AFR. Rather you must add more Fuel to the increased amount of Air in order to hit your target Ratio. Whatever that may be; 14.7:1 being the stoichiometric mixture.

It's not that these mods that improve flow require a richer AFR just more fuel to go along with the "more air".

Now, there I go joining The Griz off-topic. :eek1

That's another way to explain it, yes. And that target/best AFR will more than likely be around 13.5-14:1, given the types of fuels we use today and variations in atmospheric conditions.

Easing the flow of air in through the intake valves and into the combustion chamber by the use of airbox mods or a higher flowing air filter will always increase the amount of air that gets into the combustion chamber in comparison to fuel mist by the injectors, which in turn leans out the AFR. Therfore, you need to re-richen the AFR with more fuel mist. Once this has been completed power gains can be realized.

Adding more fuel mist to go along with more air is richening the AFR. Again, what's happening is you are leaning out the AFR considerably (more air/less fuel) by providing more intake and exhaust flow. So in turn you need to richen the AFR (more fuel to match the more air) in order to realize the benefits of higher flowing intake and exhaust systems.

Just call me half empty, but I would bet its primary purpose is emissions. Undoubtedly, the f800 has more valve overlap and duration to provide more power than the F650gs, which means more pollutants. Could help with scavenging exhaust and a freer flow, but I doubt that is why it is there. To do that requires the exhaust valve be at least partially open and opening an air valve would kind of like sucking on a straw with a hole in the side. Without seeing flow charts and knowing when the air valve opens it is all a guess. Open when the valve is still open, see straw comment, in fact it would decrease the scavaging from the cylinder, because it is a leak. Opens after the valve closes it would help residual exhaust exit the tail pipe because it decreases the vacuum effect existing exhaust creates.

Can't say with certainty what the F800GS has or what it does, but in most cases an air injection into the exhaust or SAS is intended to supply O2 for the catalytic convertor. Depending on the type of catlyst used, it requires O2 to facilitate the catalytic reaction.

The Griz, you really, really have a drive to prove you are right, don't you?

Very good point!

Nah, just want to make sure the correct information gets displayed as much as possible on this forum. This is my sole purpose for being here. It has nothing to with whether I'm the right one or not, rather whether or not correct information is posted.

I'm not worried about my ego or taking care of my large oversized head. There are a lot of folks that know just as much or more about a lot of things motorcycle-related than certain people around here. We can't always look to the same one person for the facts, because there's really no one person who knows them all, myself and you all included. I am humble enough to admit that. I just wish more would be willing to do the same, instead of feeling the need to attack others when they feel threatened that some one else might know something they don't, by claiming that what that person is posting is "opinion" or whatever they can to deflate that person and make them small so that they feel better about themselves and/or maintain their "status" on this forum.

Also, since there's a lot of folks around here that are so very bent on having no opinion-based posts, I've resorted to posting disclaimers when what I'm saying is my opinion versus when what I am saying is scientific fact and truth. I (and hopefully many others) feel this is lame to have to do, but oh well. What ever I need to do in order to not upset and/or threaten certain people.

Just look at post #14 from this thread. http://www.advrider.com/forums/showpost.php?p=14499164&postcount=14. I mean, really? After not being engaged in the thread for an extended period of time you really feel the need to try to make someone feel small because you didn't write the correct response? Because you weren't the guy who solved something or thoroughly answered a question? Unfortunately, this example is all too common around here.

We should all just realize that as humans, individually, any one person doesn't know everything or have all the answers to everything. I know I don't, and am always willing to congratulate someone when they are able to answer something I am not. Historically, I have done so.

It takes a collective of people to come together and work together to make sure we can cover all the bases regarding this bike correctly. Hopefully we can keep things more positive and collective around here, instead of constantly having "The Clash of Egos" saga on a daily basis. That form of negative interaction only slows the process down.

Lastly, I know this post will once again 'offend' or 'threaten' certain folks. We'll probably see a trail of flaming and more childish posts of fat soldiers down on one knee and such. But this needed to be said. Let's try to stay civil and work together instead of playing swords with our streams of piss constantly.

Yours truly,

The Griz

Well said The Griz. Thanks!

Gary:

My reading of Joel's explanation indicates that both the (upstream) solenoid AND the reed valve must be open for air to be added to the exhaust. The solenoid makes it a possibility, the reed valve decides the timing. The reed valve will only open when there is a vacuum present in the exhaust system, so I think scavenging is unaffected and the "drag" from the vacuum effect would be reduced or eliminated....?

Griz
I didn't read any of your post because it was too long and I didn't have the time. But in any case, you're wrong!



Sorry man, couldn't resist.

Guess he didn't get that memo....

I knew you would have a good sense of humor about it.

Cheers

(Chuckles to himself and decides it's time to go to bed...)

Joel, thank you for your valuable input here. I love it when 1950s mechanical knowledge is shown to be so hopelessly inappropriate when applied to modern machines.

Hey Rusty Nutz, stop rubbing your nutz on rusty things and realize that although most of Joel's explanation, though overly complicated, is correct, one major statement is not:

This information is straight up false. If you want to buy into it, go ahead. But I'm not going to let false information by Joel Wisman and crew go unchecked again, especially after him and his crew's hissy fits about me not posting "fact".


And once again, I'll repost the truth about it:

PROOF:

Look at the Accelerator Module and Booster Plug threads. These items would not be selling, and would not be installed and reviewed with such rave results unless they were ACTUALLY working. For many people who are running higher flowing air filters and higher flowing exhausts, keeping the bike in stock form is simply not an option. The bike is already tuned very lean from the factory to meet emissions standards. So when folks are adding a higher flowing air filter and higher flowing exhaust, they are experiencing much worse lean burning symptoms. Surging, jerkiness, etc. The BMW ECU can simply not "learn" or "re-map" far enough on it's own to account for these additions in EASE of flow on intake and outtake . It needs help to be able to richen enough, so that the rider can actually reap the benefits of their expensive easy-flowing exhaust and easy flowing air filter. A Power Commander, Accelerator Module, or Booster Plug will richen the mix FARTHER than what the ECU can "learn" to do on it's own. And they do it far enough to the point where people are actually seeing and feeling the benefits of their expensive air filters and exhausts. The proof is in the result. Therefore Joel's statement that "you will NEVER improve HP and runability through airbox mods, filter mods, header mods, or fancy slip ons" needs correcting, because it is wrong. If you don't want to believe me, then just look at the results in the threads I speak of, and also motorcycle racing history! I mean, it's not like we're talking many many HP gained here, that is obvious. But c'mon guys, it is common knowledge that a few HP CAN be gained ACROSS the RPM range with modifications including flow and AFR tuning. I don't care if freakin' HAL 9000 is the computer controlling your bike and/or if aliens built the effen thing, you can still mod and tune the damn thing. What I'm getting at is that it doesn't matter how complicated the computer control system for the bike is; if some one designs something that ALLOWS alteration or modification to said computer control system (Power Commander, Accelerator Module, Booster Plug), power gains can be realized. Because at the end of the day, what is the computer THAT YOU'VE TAPPED IN TO AND ALTERED controlling? Air, fuel, and spark on an INTERNAL COMBUSTION ENGINE.