<font face="Comic Sans MS">Well since the K&N is capable of flowing a bit more air than regular filters technically you might lose a bit of gas mileage. However, since your engine will only pull in as much air as it can use anyway, I would say you won't notice a difference. [img]/wwwthreads_images/icons/crazy.gif[/img] Your mileage goes down in the winter normally anyhow... [img]/wwwthreads_images/icons/crazy.gif[/img] I wouldn't worry about it.</font>
Well, in the summer I was running a good 18 mpg with stock filter and 17 with k&n. Now this winter I'm getting 14-15 with the filter. Not a big deal since you usually get less mpg in the cold months. Also consider if you let your vehical idle to warm up in the winter.
I'm a bit stumped by the lower MPG with a freer flowing filter. Is it because the increase in air allows you to burn more gas? Also, is it that the denser, cold air expands more in the engine and allows the engine to burn more gas?
<font face="Comic Sans MS">The MPG might go down as a result of an increase in air "requiring" a corresponding increase in fuel being placed in the engine, which happens because the computer in closed loop mode, wants to keep a specific ratio of air to fuel... At sea level that is 14.7 parts air to one part fuel. [img]/wwwthreads_images/icons/crazy.gif[/img]
I was going to give an example with some theoretical calculations, but I'll have to leave that for some other time...
Cold air which is denser contains more oxygen per unit volume. If you take a cubic foot of air at 90°F you can run the engine with less fuel because there is less oxygen in that air. The reason you run less fuel at higher temperatures is because you don't want to run lean or rich... But that same volume of air at a cold temperature perhaps 20°F you need to add more fuel because otherwise you would run lean..
[img]/wwwthreads_images/icons/crazy.gif[/img] Sorry about being long winded about this... [img]/wwwthreads_images/icons/crazy.gif[/img]</font>