I like the HB PDP engines myself, I think i still have a HP 40 PDP in my engine box still.
But these engines are baffle ported engines and as such just aren't timed to work well with a tuned pipe. The Schuerle ported engines can take better advantage of a tuned pipe, but even then the engine ought to be tuned for a pipe too. They change the port timing to take advantage of the tuned pipes supercharging effect.

Now you can just run a tuned pipe and not bother really tuning it any, it would look good.