Forced induction would be another scenario where your volumetric effeciency would go WAY over 100%.
The motor doesn't need to work harder to make the air go through the smaller throttle body, and the smaller throttle body will increase airspeed velocity. If the throttle body were 20MM or something stupidly small, then the motor would be working really hard to pull it's required air through it. Even if you take your 60MM TB, and port your Indy manifold, run wild cams, and port the head until the walls are as thick as aluminum foil, you still won't be much over 100% volumetric effeciency. You might hit 110-115 percent volumetric effeciency, which means that your motor is consuming 2.0 * 1.15 = 2.3L of air. This is more then compensated for in Gary's equation, though. Now, say that we are using a turbo, and run 14.7 PSI (which is one atmosphere of air). Given perfect effeciency of the motor, you have effectively doubled it's VE, and it should act like a 4.0L. that's why turbochargers work. They cram 4.0L of air into a 2.0L. In that case, the 60MM TB would be of great benefit, as you are not feeding a 2.0 any more, but you are effectively feeding a 4.0...
I have had a lot of discussions with a bunch of engineers about this, and that is where this all comes from. At first I didn't believe them, but the numbers hath spoken.

By the way, I just thought of another condition that would require more CFM from the intake stream: increased redline. We can't effectively do that to any extent that really matters, though, at least without a standalone, so it is vastly irrelevant.

By the way, the CFM numbers that Gary posted are peak numbers, which means that at anything less then full throttle at redline, the motor will require signifigantly less air.

-=B-=

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