Reply to "Size of Air Filter"

Virtually all air filters become restrictive at some point.

Some are to the point that you can feel a torque loss right off of idle if you remove all parts of the air cleaner.

One of the most restrictive filter elements I can think of are the oval paper elements supplied for the COBRA oval air cleaners. It has been called an "rpm limiter" by many.

As I recall, the early magazine testing of the 68 428cj Mustangs showed about 1/10 of a second improvement in the 1/4 mile times just by removing the air cleaners for the test.

I think someone back then factored 100hp gain at a .2 second improvement in the 1/4? I'd have to look that up though.

The most efficient filter would be one that sits with the opening straight up on top of a velocity stack.

Exactly what that translates to in HP I don't know.

I can tell you that on a 48 IDA Weber set up, the hp difference is in the 80-100hp area. That was clearly shown on a dynamometer.

Engines are usually so full of compromise to begin with, the only control we often have is where.