The most you will probably get with the mods on a Jap spec supra would be around 250-260 rwkw...
The US spec supra's would be able to hit the 300 mark as the turbos are different as well as haveing bigger injectors and a more aggressive intake cam...
upping the boost on the stock setup doesn't always work as well as you would think as the sequential system is controlled by the computer but there are some tricks you can do...
Parts are a little more expensive but because the supra was built in the US also, you have a bigger choice...
The only probalem I have had so far is Traction... It is a very fun car but fi you want the full potential you need some good quality wide rubber on the rears...
The reason for the RB26 to go into some of the Jap Supra's is because the RB26 doesn't make as much torque as the 2J...