Oem air box and I am using a drop in k&n filter. Performance is important but I live on a dirt road so filtration is key too. Does the k&n filter as well as oem? Does the oem flow as well as a k&n? What other options are out there?

 

The better the filter flows usually the worse it will filter. K&n will flow better but filter worse.

 

I read online a study someone did some years ago comparing k&n filter with several standard paper element filters. The study analyzed the ability to filter, not to flow.

The k&n did not fair well. It wasn't able to remove particles anywhere near as well as a normal filter.

If you have a k&n, and are concerned, just get an oil analysis, which will tell you if too much is getting past the air filter.

 

I'd stick with the oem filter, it's surface area is more than enough that it can flow more air than a stock engine needs. It also has an air horn built into the base of the filter, and not all of the K&N filters have that. The oem unit will filter air better than a K&N. I see no benefit in changing to a K&N filter other than cost savings.

 

This. Not exactly the point of OP's question, but often overlooked. K&N really missed the boat on that one.

 

What air horn? The k&n does not have that? I am assuming it helps for performance. So for a mild bolt on car, does the k&n outperform the oem, or is the oem better.

I will do the oil analysis next change.

Is there any air filters that flow better and filter better than oem? Sounds like no...

 

Usually called a velocity stack in the states
http://en.m.wikipedia.org/wiki/Velocity_stack

For your situation I would continue to use the factory filter, and just change it more frequently than recommended.

 

So I will need to buy an oem filter then. Any year good?

 

I run a JR filter.
2.8 microns filtering,and free flowing,and with a velocity stack.

 

Cosworth oem here