Across any filter media, there exists a pressure drop from one side to the other, because the filter media cause the direction of air flow the change and or turbulate.
The magnitude of the pressure drop relates to the speed of the air moving through it as well as how dense the filter media is and the shape of the fibers doing the filtering.
You'll note that the stock filter media is pleated. This is not just for cool looks. If you removed the paper and stretched it out accordion style, you'll find there is a lot of media there packed into a small space, far more than if the media was just stretched around the outside shape of the filter.
This is done to lower the air speed moving across any section of filter. A given volume of air moving through a small area must move faster than the same volume of air through a larger cross section of area. Generally speaking, faster air creates more turbulence around a pathway obstacle.
The paper type filter has a very large number of small pathways, so that the air speed through each pathway can be kept low and suffer from fewer air turbulence, speed robbing effects.
You CAN find alternate filter membranes that have larger pathways through it and make the overall filter media size footprint smaller and still have nearly the same pressure drop characteristics. But, it doesn't come about with just casual visual inspection. Therefore, it is generally accepted that if you change the filter media type and or size, you WILL change the pressure drop across the membrane.
The pressure drop factor is important as all the fuel jets react to the pressures inside the carb throat to change the flow rate of the fuel entering the carb throats. And, the filter membrane is one of the barriers for outside air pressure to reach into the carb throat. Remember, it is the outside pressure that pushes the fuel through the fuel jet into the lower pressure of the carb throat. You may have observed that the fuel jet supplies no fuel into the carb throat when the pistons aren't moving in the cylinders and that is because the pressure inside the carb throat is equal to the outside air pressure, so no fuel movement is possible.
The jet sizes/adjustments in the carb was selected by engineers/mechanics for the particular characteristic pressure drop the stock filter provided, and there is no mechanism in engine or carb to automatically alter the fuel jet metering parameters in response to a filter media pressure drop change.
Your question:
Okay so I know some people go to the cone air filters but I want to make things more neat. I was thinking about buying some kind of air filter then using just the foam to cover up the hole in my stock air box on my 350f. Do you think this setup would work?
A qualified yes. Assuming you wish to also change the pilot jetting, the main jetting, the slide or throttle valve jetting, and possibly the slide cutaway angle.
Also note that with decreased filter area high speed pressure drop effects are more severe and begin to reduce that actual volume that can be delivered to the engine. Reduced volume means less oxygen getting to the cylinders, and reduced resultant power, (even if you do readjust the A/F ratio to ideal.) So, it may seem to work out ok for idle and even some mid-range speeds, but you can easily lose power up around red line RPMs. Of course, that won't effect how it looks in the garage or in parking lots or pictures where people can ogle your bike and say, "neat".
what might be some issues.
I think this was covered...
Cheers,
