r motor uses the b16 casting. theres no doubt about that....but they also have WAY better pistons (11.5:1 comp in jdm form) and have been re worked from the factory as far as ports. they have a better intake mani and header and exhaust. u cant compare the r motor to the rest of the b series motors. just bc they have the same casting doesnt mean that that casting is better. stock for stock, b16 vs gsr, the gsr makes more power. period. end of story. if u dnt believe me, go to ImportReview Re-direct n check the dynos n comparisions n stuff. cant argue with a dyno chart.