A very good pipe to consider is the Bolly EQ 140R... very smooth timing, lots of power gain, but it is a very LONG pipe, tunes long, needs a long tunnel. North America importer gets about $135 USD, I think. I'm using one on my Mintor 1.70, very good performance.

Another, and FAR less costly option is the Mac's 1092, at about $80. A little heavier, and has the "tinny" aluminum sound, but also tunes very smoothly. I have one of those on my OS 1.60/Perry Pump setup - LOTS of power - APC 17 x 12N at 8500 on 15%.