Well there are some issues concerning K&N filter and max speed. Actually two friends of mine have noticed that with K&N replacement filter they see less terminal speed than the OEM air filter. For example with OEM filter they see max speed 235 km/h whereas with K&N they see max speed 229Km/h (al this with low power 5MT). I also have noticed that in speeds over 170 Km/h my friends car with OEM air filter seems to be slightly better than mine that has K&N.

I think that either 1 or 2 is true

1) The K&N filter needs cleaning that is the reason that performs worst than OEM filter at high speeds
2) The K&N filter is not so good as OEM filter concerning high speeds.

 

You do know that different outside temp can affect the Max density right?

and how does a more free flowing filter medium have less air ?

 

^ well if K&N filter is very dirty may leave less air to pass than a OEM filter in good condition.

And If with K&N filter is letting pass more air than the OEM, does the ECU injects the required amount of gas in order to take advantage of the "extra"
air?

What if you have a lot of air passing from K&N filter but you do not have the necessary fuel for this amount of air. Are you running lean?

 

If u comparing a clogged K&N filter with a almost brand new OEM filter than yea maybe that will be the case

the MAF will measure the correct air, thats what its for. the stock mixture is pretty rich, and it might get it to run even more rich.

 

I presently use the K&N filter and have seen no real difference between it and the OEM. I will say that the K&N may have a more free flowing filter material but there is also less of it then the OEM. By just looking at it I would say the OEM has over twice the surface area as the K&N. The OEM is a very good filter.

Lets face it guys Mazda engines did a pretty good job of tuning all the part to perform at the max. This is evident by the modest gains bolt on mods give the the RX, it is no different with this filter. If I was to do it again I would have gone with the OEM.

 

Yeah the K&N is no real power maker but it's still far more cost effective than the OEM ones.

 

ok, But I have two more RX-8 owners that complain that they make less terminal velocity with K&N filter than the OEM. This means to me that is high speed K&N filter may not so effective.

 

there are so many factors that govern max. speed that the only way you could know this for sure is by doing a series of back to back tests in both directions . Please do these and report back the findings

 

It's pretty hard to accurately test this sort of thing. I assume you're using the same car for both tests, swapping the air filter out for each. Which did you run first? Did you fill the car up with gas each time and do everything else possible to ensure that they were the same weight? Did you let the car cool down so that the next run was done on a similar temperature gradient to the first? Were these all at the same time of day, with minimal outside temperature differences?
Have you reset the ECU after installing the K&N to ensure that the car has calibrated itself for the air flow?

This may all seem incredibly ****, but you're talking about a 6 km/hr difference here which could be possible between runs on the same car with nothing changed. Do more tests. Graph them.

 

going for terminal speed is quite an undertaking and I doubt your air filter has much bearing on the case. absolutely everything has to be the same for you to blame the air filter.

For anyone interested in K&N filters, I suggest you read this article first.

http://www.bobistheoilguy.com/airfilter/airtest1.htm

 

Wow, I'm having serious flashbacks to the kid that killed himself in the 5-series a couple weeks ago. If you're really testing "terminal velocity" I hope you're doing it on a track. Anything else your clock is ticking.