Hi Matt, I have been watching your progress.
Are you saying that power falls off after 6,000 RPM, or that it is flat from there on?
I am not surprised regarding the IRIS experiments, I argued along those lines some time ago in respect of power output. It is affectively an economy device assisting the lower/mid range. For your application it is wothless.
You must fit a timing protractor and plot the opening and closing points on each cam relative to TDC, in order to see what is what. My bet is that it is here where you will find what is missing from the stable.
