Hopefully a healthy discussion based upon facts and not opinions.
So on to the concerns...
Physics dictate the above which is a given, there is no possible argument there.When it comes to naturally aspirated and turbocharged vehicles alike, it is hard to beat the response and efficiency of individual throttle bodies. Unfortunately because manufacturers often tend to prioritize cost over Peak power, individual throttle bodies are a rare sight in factory equipped vehicles, and generally limited only to the highest performing models such as the BMW M3 and Nissan Skyline. When cost is no object however, individual throttle bodies have several distinct advantages over their single throttle body counterparts.
Single Throttle Bodies
Most vehicles come from the factory with a single throttle body primarily due to cost concerns, as individual throttle bodies tend to be far more costly and contain far more individual parts. In a single throttle body design, air rushes into the intake manifold’s plenum when the throttle is opened. While the response is relatively quick, there is still a brief pause between the time the air rushes into and fills the plenum, and when it actually runs into each cylinder. No matter how well tuned the engine is, or how balanced and blueprinted its components are, this lag will always be present, however miniscule.
Individual Throttle Bodies
In a vehicle equipped with individual throttle bodies, the plenum if equipped, remains full of air whether the throttle is open or closed. Because of this pre-filled state, there is no wait when the throttle is opened, and air rushes directly into the engine, resulting in a crisp and responsive throttle. In some extensively modified, naturally aspirated engines, the plenum may be removed altogether, allowing room for tuned velocity stacks designed to compliment a specific power curve and make more useable power. In high horsepower engines, individual throttle bodies also tend to flow air more efficiently, freeing up power and complimenting high lift cams or high levels of boost.
So on to the concerns...
So at what point does a single throttle body become more efficient than individual throttle bodies?Potential Concerns
Individual throttle bodies, when run without a plenum may be more susceptible to dirt and dust and excessively loud for street use. These engines should not be operated in areas of excessive dust and dirt without adequate filtration. It should be noted that for vehicles equipped with mass air flow sensors, a sealed intake system will be required for proper operation, as is the case with Nissan’s RB26DETT engine, which is equipped with a standard plenum style intake manifold equipped with individual throttle bodies. Individual throttle body kits are generally very expensive due to the precision and machining required. Often at times as much as 3-6x more than a comparable single throttle body upgrade. Because of the limited power increases they may make with an otherwise stock engine, they are often times better suited as a finishing touch rather than a starting point.
The power your engine can generate can be limited by restrictions and inefficiencies. At stock power levels, these restrictions may not be apparent. But in a highly tuned engine, they can become severe bottle necks to airflow, and thus largely reduce power. Individual throttle bodies not only offer superior response, but they also reduce these restrictions, freeing up power through improved airflow, with little to no trade off other than cost and increased engine noise.