Muscle Mustangs & Fast Fords
Throttle Body Guide - Air Apparent
Understanding throttle bodies
The airflow improvements offered by the Stage 2 system decreased the vacuum (inlet restriction) present from 2.22 inches to 1.33 inches. Minimizing the inlet restriction resulted in an increase on boost pressure from 8.5 psi to 8.9 psi. If we take the change in boost offered by the upgrade 0.44 psi and divide it by the original boost (8.5 psi), we see that boost increased by 5 percent (0.44/8.5 = 5 percent). If we take that 5 percent and multiply it by the original power number (502 hp), we get 25 hp (matching the power gain almost exactly). This percentage gain in power relative to the boost and vacuum loss was consistent up to 20 psi.
We have concentrated our efforts primarily on the throttle body and air intake system, but the intake manifold connecting the throttle body to the inlet of the supercharger is equally important. The largest, fastest, most powerful supercharger in the world can be severely limited by a poorly designed inlet system, including the intake manifold. The intake design is almost always a compromise, as it must maximize airflow while simultaneously fitting the tight confines of the engine bay. Given the rear entry of most twin-screw and Roots-style Mustang superchargers, it becomes difficult to package the intake manifold and supercharger in such close proximity to the firewall.
Recognizing the importance of inlet restrictions, Kenne Bell designed its Mammoth intakes to maximize flow for high-horsepower applications (available for a variety of popular Ford modular engines). As with the throttle body and air intake systems, vacuum present in the intake manifold will reduce both boost and power. Testing on the Mammoth intake revealed an increase of 56 hp at 22.8 psi of boost. Like the throttle body, the gains offered by the Mammoth intake manifold increased with the power output.