The current owner purchased this '93 Miata with the Jackson Racing Supercharger kit already installed. When it came to us it had already received an 11psi pulley upgrade, and a rising rate fuel pressure regulator in order to compensate for the increase in boost from Jackson's original setup. Both of these combined to create one incredibly undrivable sports car. Spitfire EFI saw tremendous potential in this kludge of antiquated fuel delivery components and set to work on a properly tuned EFI system.
The whole idea behind the Miata project was to create a daily drivable car that retained factory cleanliness under the hood, and had fully functional OBD. And to do all this on the owner's budget! After the current owner was fed up with attempting to tune the rising rate fuel pressure regulator and battling the lack of throttle response, it was time to install something with full fuel control and a real 3D spark map.
We started things off by removing the factory airbox, the generic spark retarder, and the rising rate fuel pressure regulator. The primary wiring trickery that took place was the installation of an external intake air temperature sensor, as the factory one was removed when the airbox was deleted. This was accomplished without cutting or altering the factory wiring harness; which, should the need arise, will allow an easy way to revert the car back to factory specification. The installation of the MegaSquirt ECU also took place without any changes to the factory wiring harness, and the stock Miata ECU was retained for OBD functionality and to run any needed fan, idle bump, and dash functions. Yes, you read that right: no wiring was cut anytime during this project. In continuing with the like-factory theme, the MegaSquirt was hidden behind the dash, and you would be hard pressed to tell it apart from a stock Miata inside.
Hardware wise, this Miata runs a v3 MegaSquirt ECU controlling both fuel and ignition timing. The ignition system is otherwise all stock Miata components, including the coil packs, igniter, trigger wheel and two VR sensors. The under-hood portion of the fuel system is also all stock Miata parts, down to the injectors and fuel pressure regulator. An aftermarket fuel pump is the only modification to note with regards to fuel delivery. The redline is near the factory setting, at 6500 RPM.
In tuning the Miata, the primary focus was once again on its ability to be driven on a day-to-day basis, despite the radical change in engine control hardware. This meant primarily concerning ourselves with fuel economy, idle quality, and warm-up/cold starts. The Miata now gets better average freeway economy than it did before the install, and the throttle response has increased immeasurably. The cold starts have been tested below freezing, and the idle quality is like stock. There are no more obnoxious clouds of black smoke or lagging when the pedal is pushed all the way to the carpet.
Future plans for the Miata are an intercooler and more Autocross enjoyment!