Flyin Miata has done somewhere between 50 and 100 conversions on all four generations of Miatas. It had a few glitches but all were fixed. The engine was the 480 HP version of the LS3 crate motor. The new owner had Flyin Miata install the 525 HP camshaft which is a nicer cam to live with at low speeds.
An FM conversion identical to my car down to tires and diff ratios was tested by R & T a few years ago and turned a 0 - 60 mph of 3.8 seconds. I've driven several of the conversions with the 525 HP engine and they all felt faster than my car.
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Mine replaced a 2005 Saturn Ion Red Line Quad coupe. GM's best kept secret performance car. 2.0 supercharged, over 200hp at the wheels.Sport tuned suspension. A good performance coupe as well as a daily driver. I'll miss the convenience of the quad doors, but happily adapt to the level of BMW M2 luxury and hot performance. 0-60 is fun, but 75-100 is a real blast.