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The B heads ('93 to '96 MK VIII and '96 to '98 Mustang Cobra) had unique intake manifolds with a split-runner system. Called the IMRC (intake manifold runner control), the engine breathed just through the squared-off ports under light-load conditions. At heavy loads or full-throttle, butterfly valves in the intake runners would open up the circular ports, too. On paper it works well, but in reality, the butterfly valves would get stuck over time and not open fully. MMR sells an adapter plate that eliminates the IMRC, allowing you to take full advantage of the B head's potential.