Bonneville America Forums Forums Technical Forums Performance Mods Drilled Airbox

I would like to see someones airbox drilling photos. I am planning to drill out the bottom of the airbox and want to see what everyone elses finished products look like. Any recommendation on tools and procedures would be very helpful. Thanks.

I cut the bottom out of my airbox shortly after I got the bike and it is a pretty easy mod (once you get the airbox out of the bike) I used a hole saw and a demel cut off wheel. hopefully these pictures work.


with the polaris bellmouth installed in the bottom cutout

Air Box drilling scroll down about 4-5 posts, it's listed as "Freak Alternative...."

I started with a 1" hole drilled down through from the top, and did the same with the stock air filter, and could definitely tell the difference. I later enlarged the hole to the maximum without compromising the air filter seat, and installed a UNI filter cutting out the entire bottom of the filter first, just leaving the rim for it to sit on.

After having the bike foul out on me in the rain a couple of times, and finding the bottom of the air filter washed out, I have replaced the UNI with another, only leaving the bottom of the filter intact this time. In effect, except for the removed top snorkle, I'm back to a stock airbox.

It richened up my mix a bit, which I needed after installing the TORs and rejetting, and I have to say, she has never run better. Definitely not starving for more air.

I haven't pulled the plugs in a while (to check plug color), but I can say she has more top-end than ever, having pegged the speedo at 120 mph outrunning a thunderstorm recently, and she got there real quick too, unlike before when I had to have a really long straight stretch and allow her time to climb up above 110....I mean I rolled on, saw a sport bike a mile behind me in the mirror, and when I looked down I was at 120 and she may have kept climbing had I stayed in it. The Interstate was dry, as the rain was behind me, so I know the wheel was not slipping. She was rock steady though, and happy to be there. (The Flyscreen does a lot more than she gets credit for.)

I have gone over the ton a few times since, enough to know that she is definitely a lot free'er than she has been in the past, even with the more open airbox.

If I had one thing to do over, it would be not drilling the airbox bottom. Leave it alone, try a free'er breathing air filter like a UNI or K&N, and tune from there. I'm done.

I think the pods are best. I have been riding in torrential downpours and never even a sputter.

I had mine drilled out for quite a while without
any trouble. Did notice a little staining on
the bottom of the filter media. Then on a long
roadtrip in torrential rains, the bike wouldn't
go over 40 or 45 mph, uphill about 20 mph. The
bottom of the airbox was full of water, and the
filter was absolutely soaked. Fouled up the
trip for me and fellow riders while I screwed
around with it. Ended up pulling filter for
the rest of the trip. Have since installed
stock undrilled filter and re-jetted accordingly.

The down pour that come to mind would be from here in the Poconos PA to the northern end of Vermont, and it was raining so hard the whole way that I could barely see the tail light of the guy in front of me. Not a sputter the whole way. The America in front of me had the pods on too and same thing not any power loss or anything. Also rode in extreme rain this summer in the Johnstown bikefest every day at least once.

I think spray from the rear tire blasting the top of the
swingarm sprayed right up into the hole. Pods would be higher up.

Oh I agree I was just making the case that the pods would be better than an air box with the bottom drilled.

Spray from the rear tire doesnt affect the drilled airbox. I have had mine drilled for a year now and never had an issue. I ride my bike just about everyday so i have been in rain storms, torrential downpours and you name it. I live on a dirt road and have never even had issue with that. I also agree that the pods are probably the best option. That will be one of my projects for the winter this year.

Speaking of pod filters, i found these filters that are "Supposed" to be better that the K&N pods. they are only $16 each and are available on Mikesxs.com.(found them while i was researching parts for my XS bobber. It says the opening is 52mm, what is the opening size of the K&N pods sold for our bikes?

I've said this before and I'll continue to do so for lesser informed arrivals to the site. You will most probably do most of the easy performance increases eventually like putting on performance exhausts, re-jetting, removing the snorkel, better filter (UNI, etc.), and drilling slides (pre 07 models). All of these mods, other than some performance exhausts, are inexpensive. If you do all these things first and properly set the bike up, the advantage of drilling the airbox bottom or tearing out and adding pods is minimal. This had been proven on dyno test results.

My point is: spend your money on the 904 BB kit if you really want more performance and don't freak out. I still have my airbox with bottom intact and the BB kit. I'm getting over 75 Hp and 66 ft. lbs. of torque. There are people on this site that freaked (pods) and may have had slightly better dyno results than my pre BB results. BUT, most of those that did the BB and had the pods are not getting as good results as D&D (Pensacola, FL) did with my bike with the airbox.

I wouldn't spend $100., $200., or more chopping up the bike when for about $1250. you could have the BB done including all labor. Much less, if you can do it yourself. You can even swap out your barrels and not have to get yours bored. Just something to keep in mind.

I have to disagree , at least on the stock bore engine. I wish I had done a before and after dyno but the pods coupled with the jetting I have done I think was a significant change for the better. The added bonus is I have all kinds of room under my seat for things like the compressor for my Stebel air horn. It also makes pulling the carbs much faster and easier. I agree with not spending the money for the Freak kit if you are capable of making it yourself. The kit was very under whelming once I saw how easy it would have been to make.

Agreed I didn't mean to single out the Freak, that just happens to be what I used and was disappointed when I opened the box.