installed a K&N air filter last week at 30K miles. the engine idles and runs smoother and seems to have a little more zip when accelerating. it may just be my imagination but the biggest surprise is that the car shifts more smoothly. i don't understand why that would be but there is a noticeable decrease in notchiness from 1-2 and 3-4. if this continues it will be the best 45 bucks i've spent on this car.

 

well that good to hear as I also just purchased a K&N filter and will be putting it in.....

 

I'm a little confused how an air filter can make a manual or auto trans shift smoother. I think this is a case of mind over matter...

 

is the stock paper air filter that bad? When I installed the K&N I noticed nothing other than a little bit higher MPG maybe from the combination of the ztube.

It's like those tornado things you see on tv that you are supposed to stick in your intake to get +15hp, yea RIGHT..

 

I have a 300zx Turbo (2 actually). Years ago I put a K&N filter in the airbox and noticed nothing. Later on I took out the airbox and put in a K&N cone filter. I noticed exactly what you are saying. It didn't necessarily pull harder but the entire ride seemed smoother or at ease including the shifting (automatic in that one). Whether or not it increased HP I don't know as I didn't dyno it. But it is clear that the engine breathes easier. I'm sure as the auto shifts and the engine is changing speeds the freer breathing feeling the engine has transmits through the shifts. Know what I mean? The transmission isn't smoother per se, the engine it is connected to is.

The best analogy I can use is a person breathing through a straw versus breathing through a paper-towel tube. The latter doesn't necessarily make the person stronger but it makes just about everything they do easier.

 

i agree. i have a 6MT though and the shift has become smoother since i replaced the filter. maybe its like natewood said. the extra air keeps the engine happier and you don't get an instantaneous "bog down" when the clutch engages. i don't know, but i used to be frustrated with the shift from 1st to 2nd. i battled to make it smooth but was usually disappointed. now it still isn't as good as i would like but it's a 100 percent improvement.

don't know or care if it increased horsepower... just glad the car seems to run better. would like to see an increase in mpg although i was getting 22-24 consistently before. will track and post results.

 

a stock paper filter with 30K worth of dust and bugs might be

If you're starting with a really really dirty filter, ANY filter will make your car sound and run smoother.