WR450 Air Box Mod

22 replies to this topic
  • Indy_WR450

Posted March 04, 2003 - 04:32 PM


I just finished modifying the airbox on the WR450. After close review and removing the snorkel as everyone else did, I noticed that the seat bottom has a large protruding bulge that nearly seals off the 2 main air intake openings next to the battery. I looked at the rear fender as it contacted the air box and using a dremel grinder cut away the air box up to the two extruded flanges for the battery tray bolts. This creates a nice 5" wide x 2" high arched opening. Now I had to dremel grind the battery tray/ air box lid. I cut away the rear half on both sides where the old snorkel fit into and left a 1/2" wide strip down the middle where the center support bar can remain to support the battery wall. I beleive that a single centered large opening creates the best air flow in the rest of the box. After slotting the left rear number plate to match the right side, I can now look in both number plate slots and see the entire bottom half of the air filter. I relocated the coolant lines and I will relocate the electrical connector just in front of the battery before I am complete. I am by no means an expert at bike set up, it did not take much analysis to figure out that the bike was starving for air. I just did not like the idea of drilling holes in the side of the box. The battery has to stay I love the electric start. I wish I could attach images but I do not have a server to put them on. I will email pictures to anyone that would like to see the mod and they can post it if they feel it is worth while.

  • David_Gronlund

Posted March 04, 2003 - 04:53 PM


WOW, you are a lot braver than I am. I thought about doing what you did, but chickened out. That's a lot of cutting you did. Are you sure that the air box's strength wasn't compromised? The battery is pretty heavy. I would be scared of it not being supported properly now. I am not looking at the bike now, just trying to picture in my head what you did. It may be fine.

The 1" holes I drilled in the air box for the snap in vents are not visible at all. The side of the air box on the exhaust side of the bike isn't really the air box. It is a false panel riveted on to the outside of the airbox with a 1" or so gap between it and the airbox. It is there just for looks and to make a smooth line for the side panel. I drilled those rivets out and put 4 out of the 6 vents there, and up high so water would have a hard time entering the air box in the event of a good splashing. I screwed the false panel back on instead of rivets so I could reach the vents easily to pop them out and clean them. The 5th vent is right in the front of the air box up high behind the shock blatter. The 6th is on the back of the air box up high on the coolant bottle side. You can see this one if you look into the hole I cut out in the side panel.

  • Indy_WR450

Posted March 04, 2003 - 05:02 PM


Hi Dave,

I was careful to leave all the corners and beefed up sections when I made the hole. The box is constructed of very heavy plastic. I feel the integrity is still good but only time will tell. The box has extra heavy corners and beef where it bolts to the rear subframe. I am confident it will hold up. I was more concerned about the weight of the battery and if those cuts would weaken the tray. The tray remains very sturdy. I will let everybody know how it hold ups over the whole summer.

  • David_Gronlund

Posted March 04, 2003 - 05:24 PM



I just went out and pulled my seat off to try and see what you did. The air box is pretty beafy back there. You should be alright if you were as carefull as you said about keepng the strength points in tact.

Like you said though, only time will tell. keep us posted. Obviuosly I have nothing better to do than sit and wait, hehe :)

  • Indy_WR450

Posted March 04, 2003 - 05:44 PM


Hi Dave,
I can email you picks if you send a PM with your email.

  • The_Blue_One

Posted March 04, 2003 - 06:04 PM


Could you send me pics?I'll Pm my email right now.Have you riden after opening it up?Was there a noticable power increase?

Thanks :)

  • blueballs

Posted March 04, 2003 - 06:42 PM


:) Could you also email me your pic's of the air box mod? ktm520@swbell.net


  • Desracer

Posted March 04, 2003 - 07:44 PM


Are you still running the stock air filter cage? You can cut out the backfire screen and get more air, or just buy a Uni filter that comes without the screen in its cage. If anyone asks I have never had a problem running without the screens, unless you count a better running bike.

  • Indy_WR450

Posted March 05, 2003 - 12:49 AM


I have not got to the screen yet. I will remove it and give that a try as well. Thanks for the suggestion. The bike now breathes like you have the side air box cover off.

  • beezer

Posted March 05, 2003 - 05:11 AM


I have heard that taking out the screen really dosn't do much. I took out the screen on a hopped DR and didn't notice any difference. Buddies did the same thing on YZ's and didn't notice a difference. I hear it's just to keep a backfire from burning the bike up.

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  • sjw

Posted March 05, 2003 - 08:06 AM


I would like to have you e-mail some pictures/// thanks !!! :) stevewr426@hotmail.com

  • yamaharichey

Posted March 05, 2003 - 08:15 AM


Did you notice any performace gains?

  • Indy_WR450

Posted March 05, 2003 - 08:56 AM


It is a no brainer. Performance is way beter than stock with snorkel removed. I just do not know if what some of the other guys are doing works better. Dave won a race recently with a bunch of 1" dia holes in the air box. All I can say is the stock box is choked off way to much.

  • Ridin'_MD

Posted March 05, 2003 - 05:21 PM


Please e-mail me the pics if you have 'em. Thanks, Bud budlaw@hotmail.com

  • KiwiThumper

Posted March 05, 2003 - 05:59 PM


How about one of you fine guys hosting the pic's so we can all see ...... there is www.wr450.com for a start ....

  • ddialogue

Posted March 05, 2003 - 06:32 PM


Thanks for the HINT, KiwiThumper. :) You can find the photos and description under the photos link at www.wr450.com

  • Indy_WR450

Posted March 06, 2003 - 12:01 PM


Thanks for posting that Dave. I was overwhelmed with pm's to satisfy. :)

  • KiwiThumper

Posted March 06, 2003 - 01:07 PM


No problemo, always here to help :)
Thanks dd

  • msgbean

Posted March 12, 2003 - 01:12 PM


David thank you, thank you. The idea you had of drilling 1 inch holes in the fake airbox panel on the right side is a Godsend. I drilled 9 one inch holes in mine (7 on the side and 1 on each corner above the rear fender). The increased power I now have is simply amazing. Initially I was disappointed that my 450 wasn't any faster than my 426. But now the 450 is turning out to be the bike I thought I bought. It was definitely starving for air. And the added benifit is that the holes are completely concealed. I didn't install any vents into the holes because I don't feel they are neccesary since they are covered already.

  • Indy_WR450

Posted March 12, 2003 - 04:33 PM


I think we are all on the right track. One way or another we need to let this 450 take in air. Just think of how much better it will run when it is hot this summer or at higher altitudes. I like David's stealth holes under the false cover. Easy to duct tape up if needed.


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