Hi Mark, Good responses from all those above,..... but, there are some other factors involved.
Motors are one of my favourite topics, (and a very very involved one) but, I will keep this response fairly simple/low tech.
In the early 60's there really was no other choice for a motor to power a model slot car other than 3/5/7 pole train motors, they did work well, and were certainly developed over time by Pittman etc., to more meet the needs of the emerging slot car industry/market. While they did get quicker, and lots of go faster parts were introduced, they were still on the long side (magnet on one end, and long armature) and were basically only useful for inline configurations. Enter the Mabuchi 36/26/16D motors (early/mid 60's) which were much shorter in length, and while not only more powerful/higher revving they critically allowed the motors to be placed in sidewinder/anglewinder configurations, Additionally, the 26/16 D motors were significantly lighter, which greatly enhanced handling.
Current "Open" motors are a long long development progression of the 16D, but are today much much smaller, much more powerful, and will rev in the 150+K range with massive torque........this all costs money, and these are in the $300 and up range per motor, with costly rebuilds required after every race.
By contrast, the motors powering our little plastic cars are not designed for slot cars at all, they power electric toothbrushes, electronics, car mirrors etc. and while the slot car companies, (Slot-it/NSR etc.) can have some input into magnet strength/arm wind, they are essentially "off the rack" made by Mabuchi/Sun etc, who produce millions of these motors.
To keep costs down, particularly for the tiny percentage of motors the slot car industry uses, conformation to a motor manufacturer's offerings is essential.
As far as 3 vs 5 pole,.....well, 3 pole is less expensive to manufacture, that is why the major motor manufacturers produce them this way, and if well balanced, they are perfectly smooth.......well up to 150_K
If you are looking for a motor (slotcar) that is rebuildable, ProSlot has a EuroMk1, that will keep you happy, and it is no more expensive than motors from Slot-it/NSR etc.
Mark, this a very simplistic explanation, (my two typing fingers get tired)......if you need more please holler.
Hope this helps.
Cheers
Chris Walker
A few early train/slot open frame motors (mainly Tyco)..........long buggers, but still a lot used in Vintage race meetings
An "open" GP27 motor (still 3 pole).......two thirds the size of a Slot-it 21/25K FC130 motor........unbelievable power (and cost),.....and you will need in excess of 10 amps to make it tick over.