[Richard L]

I belive you are running too rich to obtain good power. Dumping fuel for suppressing knock is not a good idea.

Ideally you need to run leaner and add water to suppress knock Since you cannot tune the fuel map. May be you can try the following:

1) Increase boost beyond the map sensor range
2) clamp the map sensor output so PCM cannot add fuel based on boost.
3) reduce fuel line pressure.