The BP has 2 stroker kits available, 1 for 2.0L from Flyin Miata, and another for 2.2L from Maruha Racing IIRC. Both are around 2-4grand. The perfomance increase is around 60hp for a stock motor and much more for a boosted application with supporting mods/ecu and such. Ive looked deeply into it and the Flyin Miata one from what ive hheard/seen is the most reliable as it uses H-Beam rods and forged pistons with many different compression ratios based on needs.