[QUOTE] The old Trumper SpeedTwin was a smother motor than the Bonnie, for sure. Of course that was back in the mid 60's and then, as now, the main thing people looked for was... Power... and the Bonnie had more, so it attracted more customers.[/QUOTE] Iirc, the 500 speed twin was the motor that eventually became the 650 pre-unit, then the 650 unit, then the 750 engine in the Bonneville and Tiger series. I have also read that it was smoothest in 500cc form. The 500 engine in the T100R Daytona and the TR5 series bikes was, again, iirc, an upsized 350. The latter engine vibrated much worse than the former, except when the larger engine was "hot-rodded."