The secondaries are needed down low or you bog. If the intake manifold was like on the ST220 or even the Taurus, the swirl/tumble effects would allow for no secondaries and still have good low RPM performance. As you can see around 3500RPM there is not a HUGE jump, but rather a smooth curve. This means the secondaries might need to be opened just a little sooner, but still needed due to the runner config.
Oh, and we just went a little higher today with 93-ish octane gas. Returnless fuel systems are pretty cool once you figure out how to play with them.
