We're using a FAST XFI engine-management system and MSD's 7531 Digital-7 Programmable ignition box to light the fire in our T-top coupe's Paxton-blown Keith Craft 347. These two devices are, without question, the most important 12-volt-initiated components in the car.
While installing these two systems isn't difficult, we've decided to personalize things by not putting the boxes in the coupe's passenger-side footwell-a common location for race 'Stangs. The custom install will maintain a street-car look for our interior and enable a copilot to sit comfortably in the second seat.
FAST makes harnesses for its XFI engine-management systems that can be custom-ordered and made for a 'Stang's specific needs. You can probably make your own harness, but this setup is plug and play, and it fits perfectly in the engine compartment. We began by laying out the harness and finding all of the connector locations on the engine.
The holes in the coupe's firewall were filled and smoothed over during the body-and-paint phase of the project, so a 2 1/4-inch opening had to be bored into the firewall to pass the XFI wiring between the engine bay and the passenger side of the coupe's interior. Once the harness is in place, the large, rubber grommet seals off the firewall.
All of the XFI's connections are made with weather-pack couplers similar to this one. This locking-style coupler guarantees solid communication between sensors and injectors, as well as the XFI processor, and protection against water, dirt, and other matter that could cause the XFI to malfunction.
Since we're not using a glovebox, we mounted the XFI processor on a piece of sheetmetal that was sized to serve as a glovebox-delete panel. With the processor in clear view from the driver seat, we can keep an eye on the 347's firing activity via the LED bulbs running along the face of the XFI unit. The wires that connect to the XFI can only be plugged in one way, so there's minimal chance of messing up. Think square peg, round hole.