1 Holley’s new self-tuning Avenger EFI is a stealthy bolt-on throttle body fuel injection system for classic Mustangs. This is the 700-cfm system (#550-400) engineered for up to 400 horsepower applications. The Avenger EFI 4V TBI system hides beneath your air cleaner and is undetectable at first glance. Even the pressure and return fuel lines cannot be seen because they enter from behind. The complete system includes four-barrel throttle body, harnesses, electronic control unit (computer), electric fuel pump and filters, fuel pump block-off plate, clamps and attaching hardware, gaskets, throttle position sensor, coolant temperature sensor, and an oxygen sensor that installs just beyond exhaust manifolds or headers.