How to get rid of the WR450F airbox lid

People keep saying the WR450F battery carrier in the airbox lid restricts intake air flow in an unacceptable manner. Took off the seat and saw the misery. I decided i'll give it a try and came up with the following goals:

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[*]for the time being weight savings is considered secondary

[*]retain sealed acid-lead battery

[*]no cutting or drilling of genuine bike parts

I took out the airbox lid and compensated the gaps at the screws with stacks of washers and then decided where to place the battery. As replacing the relais with solid state high current FETs will be a future project i settled on the following battery placement:

<ul type="square">[*]hovering above the air filter

[*]front side jammed against the rubber flap folded up

for cushioning

[*]front lower side resting on airbox opening

(plastic on plastic, bad long term setup, will

need some rubber spacing, from an old tube..)

[*]rear battery end put into a custom bracket

framed battery

[*]braket will rest on bike frame via a hardwood pole


[*]braket will be pulled forward (thereby jamming the

battery against the stock rubber flap) by DIY rubber

o-ring made from an old front tire tube

result looks like this:small pic

This dfinitely is a much bigger intake area than before, but of course it still is slightly more restricted than a battery less airbox.

the whole project is documented here:WR450F battery bracket replaces air box lid


The main problem is that the 8mm diameter hardwood stick i am using to support the bracket is slightly too high to allow the seat to correctly latch (e.g. to NOT sit on the support stick)

Intermediate solution was to cut a "notch" into both ends of that stick

2mm lower thus making the whole setup sit 2mm lower in the airbox. This way the seat can be installed w/o problems.

As this weakens the wooden stick i am worried about durability. Long term solution will be either

<ul type="square">[*]replacing the wooden stick with a hollow brass tube

[*]using a steel bracket shaped like that

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which would eliminate the need to cross sides right below the seat's plastic moulding.

Engine noise is greatly increased though. But the tone is a super deep one, effective only at wide throttle openings at mid rpms. Not that there is anything wrong with that, mind you... :)

I'll keep ya posted on the refinements.


pretty sweet idea !! :)

:) i was thinking ... don't worry i didn't hurt myself. :D i looked at your pics again and thought of something. where the dowl whole is on your bracket ,mark the frame of the bike where the dowel holes are and drill a 3/8" hole there and use self tapping screws to hold the battery in place. this also eliminates having to worry about the seat latch. just a thought.

drill a 3/8" hole there and use self tapping screws to hold the battery in place

I hear ya! But currently i'm still a bit intimidated by the idea to drill holes into my rear frame, albeit them being only of a small diameter. But you are right this way the battery will stay put even when casing a double.

However, when i try to picture the load a rear frame upper tubing will theoretically see during heavy casing or my fat ass landing on the seat, i think that vertical holes through the tubes will weaken it less.

I'd guess that typical stress from catching the rear on some obstacle or flipping the bike upside down wil try to pivot the rear frame more around a horizontal axle that around a vertical one. Hence vertical holes will have less impact on real world frame strength.

I'll give the various options some additional thoughts while the Austrian weather still is as shitty as it currently is.


I like the idea. I would be very nervous about drilling any hole in the subframe, no matter how small. :D Might not be too good. Also, it doesn't meet your objective of not modifying any of the stock parts.

I wonder if the frame could go on the back of the battery instead of the bottom and just sort of hook over the subframe rails :) ??

Rowdy, great post and great documentation with the pics!!!!!

How much performance difference did you feel with the air box opened up??

Rowdy, congrats on a job well done. Something has to be done about that airbox and your project addresses that issue. Here's my lousy, two cents.

But a rechargeable nickel cadium battery, approximately the size of a piece of Texas Toast, to replace the battery altogether ($$$$). Save some pounds, use only a portion of the existing cavity and cut away the rest of the airbox.

But what about that cheesy, fake air cutout in the left rear side panel. What's a sano way to do that ? Buy a YZ450 left rear side panel ($$$$) and cut out the portion that would interfer with the side door for the air filter ?

These things are keeping me awake at night. :)

Hey Rowdy, Is it faster after the mods???

does anybody know if a YZ left side number plate panel fits?

the standard airbox is a dog!

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