air box vents for 650l?


5 replies to this topic
  • xr650l bum

Posted November 10, 2006 - 08:02 AM

#1

I am going to install some vents in my air box on my 650l! Has anybody else done this? What suggestions can you make? Did you see an increase in performance? Thanks

  • XR650L_Dave

Posted November 10, 2006 - 09:25 AM

#2

I'm quite sure there are gains to be had. jetting will need to be a little richer, and the performance gain will be somewhat limited if you have the full stock exhaust.

It could be quite loud out the airbox, depending on how you do it. take off the side panel sometime...

water crossing capability will also be limited by where you put the holes.

Dave

  • machman

Posted November 10, 2006 - 09:32 AM

#3

I'm suspicious about their being any performance gained by this. If you've already removed the snorkle, I'm not sure how much more air this will let in.

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  • Phuzzy McPhuzzface

Posted November 10, 2006 - 11:07 AM

#4

I'm suspicious about their being any performance gained by this. If you've already removed the snorkle, I'm not sure how much more air this will let in.


x2.

What many do not consider, is that an airbox is a tuned chamber designed to resonate with the intake pulses, and actually assist in creating a positive-pressure environment that aids in pseudo-compressed air for the intake charge.

Too many folks just lob on a can/pipe and a K&N in a gutted airbox without any science behind the change. The LAST resource for performance claims should be the manufacturer.

  • eastreich

Posted November 10, 2006 - 12:42 PM

#5

x2.

What many do not consider, is that an airbox is a tuned chamber designed to resonate with the intake pulses, and actually assist in creating a positive-pressure environment that aids in pseudo-compressed air for the intake charge.

Too many folks just lob on a can/pipe and a K&N in a gutted airbox without any science behind the change. The LAST resource for performance claims should be the manufacturer.


Although this may be true for every crotch rocket made, the "tuned chamber" does not really apply to a dirt bike. The air box on a dirt bike is 99.9% of the time the largest spot that the manufacturer could find to stuff in the biggest air filter they could (if they truly cared about the performance in the first place). The only manufacturer that truly seemed to care was KTM, that is why you have the 'not-always-right' linkless shock. It was positioned to the side to allow for a straighter intake track on their 2-stroke line way back when.

It is very true that a tuned intake should not be messed with. Many hours of engineering and fluid dynamics go into the designing of a proper performance airbox. But in the dirt bike world, this isn't necessarily the case.

In the end it may not be advantageous to open up the airbox because you can't use the extra air anyway. I've never had a 650L (I've got an R), but you may not have enough intake vacuum to use the extra air that the filter could get with the airbox all hacked up. If it's cammed, I'm sure it'll help, but the gain with just a pipe is probably not even noticeable (If you've already removed the snorkel). My riding partner had his R's side panel all opened up with the fancy SRC vent kit, and it didn't do a single thing for the performance of his bike (stock with a pipe) other than make him have to clean his filters more often.

And Phuzz is absolutely correct about the manufacturer claims! Numbers may be numbers, but you can manipulate them to make almost anything look good!!!

  • XR650L_Dave

Posted November 14, 2006 - 09:02 AM

#6

My guess is there's a fair gain to be had given how hard it is to get air under the seat.

Do some kind of a timed power run through the gears, then do it again with the seat off.

Report back on what you found.


I relieved some of the webbing under the seat (the molded-in seat bracing) and there was a gain just from that.

Dave





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