That's a good question. So far I've only worked briefly with the Pittman DC-84-6V. It was a bit disappointing but I'll be giving it another go.
The Kemtron X503-6V has been getting faster as I've lowered the gear ratio numerically. It has fantastic brakes and I'm going to drop the gear ratio again to 3:1 and try for a little more top speed.
The Pittman DC-65X is just a darn good motor plain and simple. Geared 3:1 and with modern Alpha tires the Harvey is almost as fast as a vintage "jail door" car on Eddie's flat road course. It's down on top speed compared to the wilder Mabuchi rewinds but the handling on the road course is excellent.
I've buzzed up a KTM 4 volt and it sounds much stronger than my Kemtron. That one will be interesting.
I also have some Ram 85's and 850's and one sacred 3 volt armature......hmmmmmm......
heya rick;
well remembering something about those ol' Kemtrons,KTM's,Pittman 85's,they werent ever used for road coarse racing,they were the DRAG RACE motors of "the day",
Having spent many days in my yout's (1960-63)at WESTERN SPEEDWAY ,in Gardena,Calif.they had a great drag strip,where you "dial up" the voltage to 36VDC,those big "padlock" motors were Drag race stuff,we used Pittman 196,and of course the 65 was a really good road race motor,i had a couple built for me by Bob Braverman,i was friends with him and his son.