I have to give credit to the compound K27 as being a smooth runner. I got mine real cheap (less than $100 back in '78) complete with micro motor aleady installed. I found micro motor-ing the old stuff does wonders. The massive gear reduction makes for a bunch of extra torque that will overcome the numerous little glitches in older mechanisms.
Along those lines, I belive the prize for the fastest running HOn3 locomotive goes to Flying Zoo's little "miniland" engines with the "slot car drivetrain". I have a Mason that I clocked at an amazing 235 scale miles per hour!
Second would go to the WSM C25 that will easily top 100 smph. On a club layout I worked on we were doing an openhouse. The NG yard was still being built and the turntable was a hole into the darkness (actually into a SG holding yard in the deck underneath). One guy had his C25 setting on the turntable lead (with a couple ties at the end of track at the pit). Another guy was switching with his NWSL class A Climax. The top speed of the climax was about 6 smph, so he was stopping and reversing by simply using the reversing toggle switch on the throttle, leaving the throttle wide open. He decided to shove a cut up the turntable lead forgetting the C25. He threw the switch, hit the toggle and the Climax buzzed away. There was an odd clunk, but no one thought anything of it. About a half hour later the other guy came in and said "where'd my C25 go?" We all denyed any knowedge. Then there was a horrific crash underneath as a SG passenger train piled up on the poor C25. It had moved so fast no one even saw it jump into the pit. I bet it was the first time the Super Chief ever got wrecked by a DRGW narrow gauge engine setting on its side across the mainline....
My All time favorite: The NWSL SP #1 diesel with the retrofit gearing and flywheel. Originally the models went about 100 smph, so NWSL put the gearing out of a Class A Climax into it. They also added a big flywheel. It ran great with a top speed of about 10 mph. The best part was if you reversed the engine at full throttle, the mass of the flywheel would pick the locomotive up, turn it 90 degrees to the track and lay it on its side.
I remember going to Webster's Hobby Shop in Phoenix when I was kid and the guy behind the counter was showing us the new engine, test runnig it back and forth on the counter. He then said "watch, it can even play dead......."
