There are actually three ways to reduce the probability of knock at full load on a turbocharged engine: reduce boost, adjust the AFR to richer mixture, and retard ignition timing. These three parameters need to be optimized together to yield the highest reliable power. What is knock? The killer of engines.
Without any sort of ignition control the recommended safe static timing is 6° (8° with an intercooler). And this is only, only if no ping is present. This will rob you of low-end torque and generally lower your HP/TQ curves.
The Bipes ACU (Auxiliary Control Unit) dynamically retards the timing of your engine to protect it from detonation or knock. The ACU uses three input parameters to control the timing: Airflow, RPM, and Intake Temperature. You can pull a total of 14° of timing. Not only will you help protect against detonation, or you gain low-end power back if you keep your static timing at 10* or advanced. The Bipes is a proven device in NA, turbo and supercharged Miatas. Aftermarket ECU and “piggyback” usually have this function built in.
Another option is the MSD Boost Control unit specifically designed for the Miata. The Bipes actually originated as a mod for this unit for added adjustability. They can still be had, but usually for the same price tag as the Bipes itself. The MSD unit retards the timing 3° per pound of boost pressure with no more that 6° of retard being allowed. When no boost pressure is present, the ignition runs at the factory timing. These settings are fixed and cannot be adjusted. With that said, you can still run your Miata advanced to 14° of timing and when it boost it will retard back to a safe 8°. If knock is still present then set your back back a little. It's a little basic but it gets the job done.
The MSD Boost Control Unit may be mounted in the engine compartment in an area away from extreme exhaust manifold heat. Most people mount the unit on the intake manifold side of the engine on the firewall. Use the unit as a template to mark the location where 1/8” mounting holes are going to be drilled.
No special hardware is needed to mount your MSD unit. Anything from the local hardware store should suffice. If you need spacers to hold the unit away from the firewall use an extra nut or a stack of washers. MSD sells a vibration mounting kit (MSD P/N: MSD 8823) that isn’t necessary, but is a really clean solution. They can be found from varying online vendors for $10 to $15.
You need to run a vacuum line to the MSD from a convenient place. Vacuum tee can be purchased from most auto part stores, and can be used to split off one of the abundant emission vacuum lines.
To connect the MSD unit some people use crimp connectors, and others choose to solder the wires. Either method works fine as long as you take your time, and do it right. To connect the unit follow the wiring diagram below:
Flyin’ Miata - MSD
The third, and in my opinion the best, option is going with a piggyback or standalone ECU unit. These units give you full control over the entire spark map; based on load and rpm.