I recently ordered a K&N air filter for my BMX 150cc ATV, but it's too big. Due to the engine being mounted towards the back of the quad (the carb is under the seat) I need to use a short filter attatched dirrectly to the carb. I found one that should fit and the dimensions are 3" round, 2" length. Will it hurt my performance by using a smaller filter?

 

According to twin air filters smaller filters in the airbox increase air around the filter.
They say its supposed increase performance.

 

I don't think it would hurt performance. My thought though is that you will be flowing aproximately the same amount of air through 10sq.in. of filter as 30 sq.in. of filter. So the smaller area filter would pass more air per sq.in. than the larger area. It may clog up a bit faster. Hence you may have to clean it a bit more regularly.

 

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Adding a performance air filter to a mini while leaving its factory pipe "in place" yields very little performance gains. Its always best to install performance pipe, performance reeds and performance air filter at the same time. And if needed, replace a small mm carb with a larger mm carb (with matching size intake). Thus, reducing "air flow" bottle neck across the entire engine. If the factory pipe and factory reeds are currently the air flow bottle neck, adding a performance air filter does very little. Isn't worth the dollars.


Also, I've been told that K&N air filter is great for "clean air" (if there is such a thing) riding conditions. If riding in dusty or fine sand riding conditions, you may want to go with an oiled down faom filter design. If you still want to use the K&N filter, oil down an old sock and slip over the K&Ns outerware. Thus, oil helps trap some of the fine dust - before it gets to the K&N filter.

If you install K&N or foam filter replacement, do remember to "jet the carb". Could range from a simple C-Clip change all the way to upgrading the pilot and main jets. For K&N, I've read one usually upgrade 5+ jet sizes on the main jet. Although, each machine is different due to altitude and weather temp and other air flow influences.

Hope this helps as well...

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