Tell us more about this engine. And what was the design goal of HPR9? Aside from a little more torque, its not on par with 8 with this setup. Was there a 9b or other? Finally, does the HPR19 have a suffix?

Every engine/pipe bulilders goal may be different.  Some want a package that will pull stumps, while others want their engines to rev to the moon so that it can win the land speed record with stock gearing.  The goal for most of my pipes and engine setups is to produce the most acceleration for a given package.  The majority of my customers are not trying to clear stumps from a logging site or become pavement racers.  To accomplish my goal, the power curve shape has to be optimized for a particular application.   Unfortunately every new test pipe is not better than the previous design.  This is why I do a lot of testing.  If every test pipe was better than the previous design, pipe #10 would have made 500 HP.

Pipe number 9 had 8 to 10 suffixes.  Why does the number of suffixes matter?  Pipe building is not like software where every new revision fixes some particular bug.  Each new test pipe hopefully has a smoother curve with a higher power average.

HPR 19 did not have a sufffix.  HPR-19 was HPR-18-? with some dimension changes.  I stopped at HPR-19 because at the time, the HPR 19 covered all of the other pipes power curves like a big umbrella.  Recent testing of new pipes on the market, shows that there is not a need to add a suffix to HPR-19 at this time.