Many of you have contemplated cutting out your old airbox, and sliding "pod" filters on. Others of you have heard horror stories about pod issues, and want to stay as far away from them as possible. I have an option that combines the added airflow of pods, while maintaining the stable airflow of the factory airbox.



Following is a frank discussion.

We all know that an engine needs to breathe in order to produce power. Consider trying to run a marathon, while breathing through a straw. It just won't produce the results you want. So, the more we can do to open the airways, the more power we can produce.

There are 4 ways to increase the amount of air flowing through the engine. 2 are easy, and 2 are more involved. The first two (the hard ones) are modifying the engine (Port / polish, larger valves, more aggressive cams, etc) and creating an artificial atmosphere (Turbo/Super-chargers). Adding a turbo to an engine will produce the largest increase of power, but it is very difficult to get right. The other options add a very small increase of power compared to the amount of time involved. These options tend to be outside of the abilities of most casual wrenchers, so we will set them aside.





The second two ways to open up the airway are relatively easy to implement, and inexpensive. These are high performance exhaust, and high-flow air intakes. Exhaust system upgrades are relatively easy and common, so I won't dwell on them too much, except to mention that almost anything is an improvement over stock.



Ok, so now we are just going to talk about the intake system. The most free-flowing intake system is the best, but not always practical. (26mm smooth bores with velocity stacks are the most free-flowing you can possibly get, but smoothbores are hard to come by and expensive.) Without living on eBay looking for a set of smoothbores, the best you can do (airflow-wise) is to go with pod style air filters. These come in many different permutations, but the best ones use a oiled foam filter element that can be washed and re-used. These flow better than paper ones, and will cost the least in the long run. Some people get lucky and have no problem with their pods, but others can never get it dialed in. The largest issue with pod filters is the inconsistent airflow to each of the cylinders. On twins, there is no problem with this, but on 4 and 6 cyl bikes, the problem can get quite severe. What happens is that as the bike travels faster, the airflow over the the outer pods causes a low pressure zone in the pod, and forcing a rich condition. You can also get a cross-wind that will cause one of the carbs to go super lean. In a multi-carb system, unbalanced airflow is a major killer of performance.





So how do you solve the problem? Some people have made shields that cover the outer half of both outer pods, but this cuts down on the amount of air that can get in, and may produce difficult to troubleshoot performance issues. Basically, there is no way to prevent the side draft issue without adding other problems. So, what do you do?





If you decide that the idea of pods is too scary, then you are stuck with your factory airbox, and it's constricted intake... or are you...?





As some people have heard, I have developed a modification to the stock airbox that greatly increases it's ability to pass air, while eliminating the turbulence that pods introduce.





This method was designed an airbox for a 750, that uses a round filter. (like a large soda can shape), but can probably be modified to work with other styles.





First, it is important to pull the airbox out, and take stock of what you have. On the airbox, you have 3 main parts that we will be dealing with. 1st is the retaining ring that you unscrew to access the air filter. The modification to this part is easy, just use a hacksaw to cut the perforated tube off even with the threaded section of the retainer. (You want about ½ to 1 inch of the tube still there, this will keep the filter in it's proper place.)





The second part we are going to deal with is what I call the pedestal. This is the part of the airbox that the filter element actually sits on. It will pull straight out of the airbox without much trouble. All you need to do with the pedestal is throw it away. Lastly, you are left with the airbox. Place it aside for the time being, and go to the hardware store. You want to go to the plumbing section, and look at the black PVC pipe section. What you want is a step-down adapter that has an ID on the smaller side of 2 inches, and an ID on the larger side slightly smaller than the OD of the filter. It should also be taller than the pedestal you removed. When you get it home, you will need to do a few fun things. First, use a 2” hole saw to cut a hole in the bottom of the airbox. Use the hole that the pedestal was mounted in as your center point. Next, use a sanding drum, or cutting tool on a dremel to route out the inside of the larger part of the PVC adapter so that the air filter can fit snugly into the adapter. You will want to trim it down to the point where it comes up about a half inch on the outside of the filter. Next, take the filter, while it is stuck in the adapter, and place it into the airbox. Measure how far above the top of the threaded section, and take note. Pull the filter and adapter out, and then cut that amount off of the small side of the adapter. Re-fit the adapter and filter, and make sure the filter is flush with the top of the airbox. Pull the adapter and filter out again, and then snag some contact cement. I used one that was billed as oil and gasoline resistant. (Important on an engine) Use the contact cement to glue the adapter in place directly over the hole you cut in the bottom of the airbox. (It is a good idea to use heavy grit sandpaper to rough up the airbox plastic to ensure a good bond.) I used the filter and retaining ring to hold the adapter in place while it was curing. The final step is to use a rasp to blend the airbox plastic into the adapter, so there is a smooth transition.





To top it all off, buy a foam / oil filter and slap it in place. With this setup your engine will be able to pull in all of the air that it can possibly want.





If you have questions about the procedure, send me a message, and I'll answer your questions.