Some other engines I just thought of taht can probably provide more power over the SH P3 are a Picco .28 pullstart or anotehr SH, one soled by LRP, the LRP z28 spec 3.

Now, I am not sure what GoldenLion has done in their current SH .28 P3, but I would not be surprised that they include all the design goodies that SH has for LRP' Z.28 engines. So, going with the LEP might only be giving you the very same performace you already have with you SH P3.