ultrataco

iTrader: (2)

I was going to get the bonez intake, but the k&n filters are cheaper and I guess just as good. Anyway, I'm thinking about getting this filter,
but it's only 3.5" in overall diameter. I don't see why that would be a problem, but I'm not very knowledgeable about this sort of thing. Most intakes I've seen are more like 5" or 6". I realize the afm inlet is only 2.5 inches, but I'm curious to know if air filter size makes any difference on anything.

I just found this.

better or no? It's an inch shorter and an inch wider.

The flange is less than an inch long on both, will that be a problem?

...and yes I'm building a box for it. I have an s5 n/a.

Sorry, but while I'm asking questions about intakes, I have two more:
1. Cone vs straight- just for looks or what?
2. Is there any real, noticeable difference (besides looks obviously) with intakes that have a flat, covered top (like the two above) and ones with a hole in the top (like the bonez and apexi)

Thanks!

RotaryRocket88

iTrader: (7)

A filter's a filter. Some have all sorts of marketing gimmicks , but in the end they all will flow way more than your engine needs.

Evil Aviator

The area of the filter material needs to be a certain size to support the airflow requirements of your engine. If the area is less than this value, then it will cause an undue restriction on the airflow, which will start to choke the engine at higher airflow levels. If the area exceeds the required value, there will be no performance increase, but the filter will take longer to get dirty.

Determining the minimum value takes a bit of voodoo math, but there is no penalty for using a filter that is "too large". Below is a very basic calculation that I have come up with to estimate the minimum filter size needed for K&N filters. I came up with it by taking the formula from the K&N website, and then tweaking it from data gained from Turbonetics and some dyno sheets. It will probably work with other pleated filters too, but not unpleated filters such as foam filters. If you don't like my ghetto formula, just go to the K&N website and use theirs.

Filter Media Area sq in * 4.53 = Flywheel Horsepower Potential

For those who aren't so great at math:
Subtract 0.75" from the filter length to compensate for the end caps. Then enter the dimensions into the corresponding web calculators to determine the total surface area.
For a round straight filter, use the "cylinder" calculator at http://www.1728.com/diam.htm
For a cone filter, use the "frustum" calculator at http://www.1728.com/volcone.htm

For those who think that the above is way too much work for something of little value, simply use the biggest filter that will fit in the car.

No problem.

Sometimes a cone type will fit where a straight type will not.

The hole is mostly just to allow for more airflow, but very little air flows through the top of the filter, so that really doesn't make much difference. Fancier filters like the Apexi have a special cone system that helps airflow, but the horsepower difference would be insignificant on a street car. If you look at most professional road race cars, they will usually just have a plain-top filter.

No

Yes

No

ultrataco

iTrader: (2)

wow, thanks!

Those filters have very similar surface area. Using your formula, the flywheel potential hp is about 260, which is way more than my lightly modded na could ever hope for, so no problem there. I'm going to take some more engine bay measurements to see if one will fit better than the other.