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Old 12-23-2018, 12:21 PM
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justbob justbob is offline
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Originally Posted by sailsmen View Post
Per K&N*

"That brings us to size.

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.

A = effective filtering area

CID = cubic inch displacement

RPM = revolutions per minute at maximum power

Example: A 281 CID Ford engine with a horsepower peak at 6,500 rpm.

281CI X 6,500RPM / 20,839 = 87.65

If you are sizing a panel filter, multiply the width of the filter area (not the rubber seal) times its length."

The panel filter would need to be 9.4"X9.4".

The filter I have is 127.25" in Effective Filtering Area.

*Note: changed to reflect MM application.

The cubic inch displacement you show doesnít include the additional amount being pushed in by a power adder and leaves out many many variables such as cams, porting, throttle bodies, and exhaust.

Either way, I trust dyno numbers more than physics with so many variables. Besides, K&N is in the market to sell larger filters..

Can you achieve a few more numbers with more airflow? Yes. But more concern should be focused on length of run and ease of flow. I remember Brian picked up over 80 RWHP just by going to a smooth welded pipe vs his corrugated hose on his 3.4 Whipple.

In the OPís case he upsized the filter but added an elbow to make it work. I only picked up another 103 RWHP in my race tune running 110 fuel, upping the boost from 20 to 26, and swapping the baby filter for a bird catcher. But then again, we had to shut her down just before 6,000 RPMS due to clutch slippage. The graph with both tunes was reaching the moon quickly before the clutch said no..

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