Selection of a filter size is determined by the needs of the particular engine it will be used on. In other words, just how much air is this puppy going to swallow? Then depending on the environment the machine is exposed to, how much more filter media does one need to compensate for dirt & dust depending on how often the end user wants to service the units.
I can tell you that the RC1290 is more than twice the filter size the Warrior needs per cylinder. In fact the ratio is 2.28 (rounded).
NOTE: We ar talking about a BAK here so when your figuring out the size requirement for the Warrior remember to use 51 as the engine cubic inch size since you will have one filter on each cylinder. If you have an air box configuration feeding both throttle bodies use the entire cubic inch size of the engine.
How to determine your filter requirements from the K&N web site.
Use the formula below to compute the minimum size filter required for your particular application. The usable portion of the filter is called the EFFECTIVE FILTERING AREA which is determined by multiplying the diameter of the filter times Pi (3.1416) times the height of the air filter in inches, then subtracting .75-inch. We subtract .75-inch to compensate for the rubber seals on each end of the element and the filter material near them since very little air flows through this area.
CID X RPM
A= _________
20,839
A = effective filtering area
CID = cubic inch displacement
RPM = revolutions per minute at maximum power
Example: A 350 CID Chevy engine with a horsepower peak at 5,500 rpm.
350 X 5500
A= ___________ = 92.4 sq in
20,839
If you are sizing a panel filter, multiply the width of the filter area (not the rubber seal) times its length. If you are sizing a round filter, use the following formula to determine the height of the filter.
A = effective filtering area
H = height
D = outside diameter of the filter
3.14 = pi
0.75 = the rubber end caps
Example:
Referencing the K&N catalog shows the proper filter for this application would be an E-1500 which is 3.5 inches tall. Keep in mind, this is the minimum size requirement. To extend the service interval and to provide an even greater volume of air to the engine, install the largest filter that will fit in the space allotted. If the space above the engine is restrictive, perhaps a remote filter arrangement could be used to gain space.
Off-road conditions require added filter area. A filter should be sized 1-1/2 to 2 times larger than normal for any conditions that could be considered severe. In this case, the E-1500 used in our example should be replaced by an E-1120 or an E-1150. For long distance off-road events, two double-size remote mounted filters would be best.
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