EFI (even just the "lowly" TBI setups) are still more forgiving of longer runners due to more complete and even atomization of the fuel out of the injector nozzles. A little more controlled than a typical carb perhaps, but certainly a carb that's not optimized for a certain setup yet.
I'm guessing that's why at least some TBI's respond well to single-plane setups, where the carb's fuel might fall out of suspension more readily and puddle.
I'm also just guessing, but some particular TBI setups may not like dual-plane manifolds as much as others due to the angle/pressure/design/number of injectors as they sit on top of the carb flange/plenum area.
Or perhaps it's the physical size of the throttle body itself? Most TB setups have much larger venturi and throttle plates and CFM ratings than a typical smaller carburetor would ever have. That alone might change the whole party, as related to how they like a wider open plenum area than would be found on most dual-plane setups.
The TBI is just making up some of the slack that carburetors suffer from.
I bet the old Holley Streetmaster Z-series manifolds would have been just the ticket for a TBI setup. They were a single plane design, with a partial divider plate separating the two banks, and an equalizer port between the two sides back near the rear of the 4/8 runners.
Too bad I sold mine with my engine, instead of keeping it. Since I was never quite satisfied at it's low rpm performance with a carburetor, at the time it seemed like a good deal to trade it for a Performer!
Oops...
Paul
