airbox air pressure

I have read numerous threads on air box mods etc. I did the flapper mod, the AIS removal and have a slip on RS2. The bike ran great! I decided to get a fmf tuner and try running with the airbox door off completely. So I took the door off and before i hooked up the tuner i wanted to take a test drive, just to see what it felt like. I found it vary odd that right away it seemed to be running to rich on the bottom, had poor low end but once i rang its kneck a little it picked up and performed with no back fire or stalling at all. This i felt was was strange since i figured running the airbox door off should of leaned it out. When i got home i was enjoying the cool airbox noise when i put my hand next to the side cover and noticed air being forced out. After close investigating i concluded that the airbox is actually pushing air out at a pretty good pressure whenever i hit the throttle. Now i am really stumped. Whats happening? Did i screw something up? How do i fix it and once i plug my tuner in will the problem be solved or is there a certain direction i should move in thats diffrent than the norm either with the settings or the setup. I have herd of others going without the airbox door and no complaints. Ill put it back on if i have to but i thought the first rule in horsepower was more air in more air out = more horsepower

Not sure what you're talking about.

I ride around without airbox door on 95% of the time.

It's been one of the single best performance upgrades I've done to the X.

There's nothing to suggest the X or R has a pressurized airbox. Lot's of people modify the airbox from stock and find it greatly improves performance.


Since our bikes are EFI controlled there's a chance the bike could run rich when you first get started.

I doubt you've done anything wrong. No idea what you were feeling. Were you riding around with side cover off as well as no airbox door?


My airbox door is removed, but the side cover is still in place.

I was not riding when the air suction occured. It happens when sitting still. I gun the throttle and air gets pushed outta the air box. I am not saying the air box is pressurized only that air is coming out of it insted of in. This is contrary I know.

I can't imagine the air box having a positive pressure, while the bike is running properly, or at least smoothly.
...a backfire, or some other, noticeable condition would be needed....and definitely affect how it runs.
You may just be feeling turbulence and are confusing that with ":blowing out"...maybe?
...maybe an exhaust leak nearby?...again should be obvious.
Lightly, tape some cardboard or plastic over the hole, and see if it blows off...may tell you more than what your hand feels.

Pressure waves !

motokid wrote:

Not sure what you're talking about.

I ride around without airbox door on 95% of the time.

It's been one of the single best performance upgrades I've done to the X....

Really? Makes that much difference?
I hadn't thought of actually removing the door, easy enough to do. I don't see any harm. Do you get alot more airbox noise coming up at you?

My friend and I have been going back and forth with this idea of running no door. We decided to take it off but have a good filter on there. The main argument was that his previous KTM bike doesn't have a "door" like the wrr. You take off the side panel and the filter is right there. It does mean, though, that you need to clean that filter on every ride.

One thing is for sure: the wrr needs more air... serious amounts.

For riding on the street, the airbox door being off is not only perfectly safe, but a fantastically free power upgrade.

yes - there's more noise.

If you don't like it, put the door back on. Free again.

I would NOT suggest doing this if you don't have a fuel programmer.

I would not do this if you ride in dusty, dirty, off-road conditions.


But for street riding with a programmer -

Stock pipe and all the updates and programmer plus K&N filter.
I'll give it a go.

Rapid Dog wrote:

Stock pipe and all the updates and programmer plus K&N filter.
I'll give it a go.

With that stock pipe you may not feel much...it's a giant cork on the system.


Give it a go though. Report back what you find.

Will do.
I also have a Yosh RS2 but switched to the stock pipe due to deciblism.
Feels like about 2hp set o the pants diff maybe.
I punch a hole in the stock pipe to egress a little more flow...

Rapid Dog wrote:

Will do.
I also have a Yosh RS2 but switched to the stock pipe due to deciblism.
Feels like about 2hp set o the pants diff maybe.
I punch a hole in the stock pipe to egress a little more flow...

Good for you. How's the sound of the stock pipe with that hole?

Not alot of diff...but then I regularly wear earpugs. I've only been down to the gas station and back since doing the misc. farkles, wiring, IMS, etc.
Going on a long(er) ride this weekend to see what it's like to ride this lil tiddler some real distance.
Considering a 9 day trip in March.

Rapid Dog wrote:

Not alot of diff...but then I regularly wear earpugs. I've only been down to the gas station and back since doing the misc. farkles, wiring, IMS, etc.
Going on a long(er) ride this weekend to see what it's like to ride this lil tiddler some real distance.
Considering a 9 day trip in March.

Where you live? Generally - don't have to be specific.

SoCal High Desert...

motokid wrote:

For riding on the street, the airbox door being off is not only perfectly safe, but a fantastically free power upgrade.

yes - there's more noise.

If you don't like it, put the door back on. Free again.

I would NOT suggest doing this if you don't have a fuel programmer.

I would not do this if you ride in dusty, dirty, off-road conditions.


But for street riding with a programmer -

I tend to agree with you: there is a reason for the airbox+door... but I'm still gonna ride it off road with no door. I just can't figure out why it would be okay on a dirt bike but not on our wrrs..??

WRX17 - You are correct on the positive pressure out the airbox from idle when you give it throttle. Being basically 1/4 of an R1 motor, our bikes are built for higher revs and consequently higher peak HP numbers. This entails a relatively "hot" cam with lots of overlap. This is the opposite of a calmer cam in a detuned motor that is designed for higher low RPM torque. The cam overlap creates the pressure pulse.The flapper thingie was designed to counter some of this, but of course its a tradeoff and that robs some high end power.

An airbox is basically a Helmholtz resonator chamber and is tuned to perform in a relatively narrow RPM range. Different size = different range. Exactly the same principal in the exhaust. Some two stroke exhaust pipes, like the FMF Gnarly, are for low down power and others for high RPM power. I've read the power differential from a properly engineered airbox can be 8 to 10%. A lot, but it comes only in its narrow designed RPM range. Consequently, most people are finding better overall performance by opening up the box, Helmholtz be damned, and going for max breathing and maximizing the WR's high rev abilities, then getting the low end back by tweaking the CO settings and aftermarket fuel programmers. I've read the FMF Mega Bomb header helps down low, but I don't understand its physics.

Warning... I did NOT stay at a Holiday Inn. I had the same questions as you and spent way too much time with Google to glean all of this.

zinx wrote:

I tend to agree with you: there is a reason for the airbox+door... but I'm still gonna ride it off road with no door. I just can't figure out why it would be okay on a dirt bike but not on our wrrs..??

Why what would be okay? I don't follow what you're saying.

What's not okay on our bikes?

motokid wrote:

zinx wrote:

I tend to agree with you: there is a reason for the airbox+door... but I'm still gonna ride it off road with no door. I just can't figure out why it would be okay on a dirt bike but not on our wrrs..??

Why what would be okay? I don't follow what you're saying.

What's not okay on our bikes?

I'm comparing dirt bikes with no closed airbox system to our very sealed air box with door. It makes me question why, for example, on a ktm 250 you take off the the side panel and you're directly at the filter and on our wrrs it's not a good idea to take off the door when going off road. What's the difference ; that's my main question.

what are your thoughts on this?

cheers

I think it's simply a maintenance interval thing as well as an emissions thing.

On a KTM, and a dirt bike in general, you're gonna be cleaning things every ride.


Our wr250's are street bikes. Dual-sports. 3000 mile oil changes. 26,000 mile valve checks.

A huge selling point is how maintenance free these bikes are. Yet still bullet proof.

When you remove that airbox door you need to be a bit more diligent with your checking things over.

If you're obsessive-compulsive about air filter cleaning and oiling you're probably okay with no door regardless of riding conditions.


From the emissions point of view, it certainly helps to clog up the system and prevent a free flowing intake.
It also cuts down on noise.