K&N Filter Tops

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Actually a larger air filter(taller than 4") will start to rob HP. Carbs and engines rely less on the amount of air, but the velocity. Look at runner designs in heads. A smaller runner creates a higher velocity, making more torque. Whereas a large runner flows more air but with less velocity, making less low end torque but better for top end HP. That's why a head and cam mismatch can make for an engine that won't run good. For example, Petey-Pablo's filter setup may be robbing some torque, but may make better top end HP. On a big block, it's worth the trade off. A small block, however, would not benefit at all from a taller air filter.

Back on the topic at hand, I can see where the Xtreme top can disturb the airflow. In theory, it should make more power, but airflow characteristics are kinda wierd and hard to understand.