On August 2006, I have installed a Rotrex Supercharger Kit by www.miatadynamics.com. Installation was extremely easy and minimal invasive. The Rotrex centrifugal supercharger is very compact and uses its own lubrication system. It has a thermodynamic efficiency similar to a turbocharger (~75-80%), unlike the Eaton positive displacement blowers which are widely used in miata applications. This leads in relative low intake temperatures, reduced detonation issues and excellent power output. The centrifugal superchargers produce boost relative to engine rpm. This fact retains the stock driving characteristics of the car, with a smooth linear power output. Here is a graph presenting the boost rise relative to engine rpm: 
I use the SP30-74 supercharger with a 90mm pulley. This gives 8.5 PSI at the rev limiter.
The dyno of the car showed a 68% of power increase:
164 rwhp (190 bhp @ flywheel)
17.8 kgm rear wheel torque (21 kgm @ flywheel)
This dyno was done on the hottest day of the summer (40+ *C), when the car was non-intercooled. There is also a comparison with the stock power curve.
This was the look of the non-intercooled setup:
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The car had absolutely no detonation issues in the hot Greek summer. Even though, I decided to install a side-mounted intecooler, in order to be as safe as possible when I torture my car in the track:
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So the engine bay now looks like this:
The fuel injection and ignition timing is managed by an E-Manage Blue Unit, which is connected to the factory harness with a Boomslang Plug’n’Play harness. I use 310cc Nippon Denso Injectors and I monitor the Air/Fuel Ratio, the Exhaust Gas Temperatures and the boost level with a Zeitronix Wideband O2 sensor.
After six months, I must say that the car isn't really what I expected... It is far better than that! It is fun to drive, it has no reliability issues, and as a bonus it holds the miata lap time record in Megara Racing Track in Athens.
