Before any one turns the air box into swiss cheese, consider that the next obstacle is the size of the venturi of your carb.
A topic that's been dead for over 4 years. Question to all who put some holes into their airboxes. Don't you have trouble with water/mud entering the inside of the airbox ? And why did you decide to do it ? Good results ? Waste of time ? (Name your bike and mods done)
My DRZ came with the whole side of the airbox drilled... lots of 1/2" holes. It's been fine with dirt and light mud but I'm concerned with water crossings. I'm going to replace the airbox and cut it on top like everyone else does. Not sure what the PO's plan was.
I had to cut the intake duct to my airbox in order to relocate my VR into the path of cooler moving air. I used a roto-zip but had to clean up the edges with sandpaper because the cutter got too hot and melted the plastic dust back onto the edge. It was expected and cleaned up fine. also the VR worked much better in it’s new home. The VR under the seat was a total design error on the part of the good engeneers at BMW. It was great when all the wiring was new but after half a dozen years I would cook a VR every summer. Just because it is engeneered by pros.. doesn’t make the best of possible options.
OK I realize this thread is eons old but if you want to make nice clean holes in plastic use a step drill bit. You can turn it as slow as you like and it works great.
The drag race guys know a little bit about making HP. Most of these bikes run an air box that is much more than 3x the displacement of the motor. It will still have no more than a couple of snorkels of not more than 1.5" ID at the entrance and tapered up as it enters the chamber. They are after still air at the carb entrance and good flow into the mouth of the carb or throttle body. They really don't care about sound or water protection or dirt for that matter. Factory air boxes are mostly designed to (1) fit in the chassis, (2) keep intake noise down, (3) allow adequate air into the motor. Properly done they can make a big difference in the power output of the motor. Keeping in mind that they really don't care about drive quality as the motor is either idling, on the 2 step with the throttle wide open, or at wide open throttle. All of which are important on a street bike or dirt/trail bike.
Not a race machine, just a humble XT250. Implemented the 'must do mod' to improve performance of removing air filter lid (big hole in the top of the airbox) fitting a one size bigger main jet, and shim the needle. Not necessary to 'shim' the needle on my Japanese model as the needle comes with adjustable grooves (US model doesn't). Did it go better? Thought so without a doubt. After about 6 months started to notice for the first time a hesitation on overrun when you rolled back on the throttle. Once I became aware of it, started to focus on it, till it became really annoying. Fixed it by dropping the needle back to its original position. So now its just one size bigger main jet and an open airbox. Ran it like this for about 2 years. One day just out of curiosity I decided to refit the air box lid. Way quieter, and didn't notice any drop in performance whatsoever. So now its back to standard except for a one size bigger main jet. To much of a hassle getting the carby in and out of this thing to swap the jets around just to compare. So my experience: All opening the airbox up did was create a lot of induction noise, which created the illusion of significantly improved performance. To really know if opening up the airbox on any bike actually improved performance someone would need to do a series of comparison timed runs on a set course (representative of how the bike was to be used). I doubt you could prove anything conclusive on a Dyno because of all the real world factors that come into play.
someone said earlier on that one factor engineers design for is ease of maintenance. from personal experience I'll say no..... no they don't. I doubt that is even a consideration
The engineers are not the ones doing the maintenance so they really don't care... Does it fit and is it cheap to make are the main goals.
Blanket statements are commonly wrong. This is clearly a your results may vary. Butt Dyno is not accurate, more noise is usually equated with more power. With exhaust, air box, jetting, ignition curve and cam change power can be found,. Sometimes significant, sometimes small. The bike will not longer be emissions legal, may not like rain and water crossings, and engine life can suffer. Not to bash Harley, just that they are commonly modified. There have also been a lot with dramatically shortened engine life and poor ridability as a result of chasing horsepower. I can attest many of them have impressive straight line acceleration. They are a pain to ride most of the time. A step drill or a hole saw are inexpensive and generally give good looking results. A hot knife of some sort usually leaves a melted plastic ridge you have to clean off. The deburring tool can work well. Rod
ahh yeah, old threads. is been my experierence that generally removing a snorkel is all thats needed for air volume until you get into engine mods.
