The amount of hype regarding the 21″ intake length was too much to ignore and we decided to redesign our entire airbox area to accommodate a nice smooth radius 21″ intake. On the dyno however, it was clear that the magical 21″ intake is not all its cracked up to be Atleast with our engine and the Skunk2 intake manifold.
GREEN: K&N 2.5″ Filter 9080 – Attached directly to the throttle body.
ORANGE: The Magical 21″ intake with K&N 9080 Filter.
BLUE: The Magical 21″ intake with an additional 16″ 90 degree intake tube (So 270 degrees of bends and 37″ total length) K&N 9080
RED: 16″ 90 degree shorty intake tube with K&N 9080 Filter.
NOTE the torque differences 4500 to 5500.
We also tested while covering about 25% of the filter area and there was no change in power, this was to learn whether the filter was able to flow enough, since its relatively small compared to others.
These runs were repeated about three times back to back changing configurations each time and the results were nearly identical each time.
In previous testing, there was no discernable difference between a 2.5″ vs. 3″ OD Intake tube.