The round finned heat-sink that Marty saw at the Group-C race at Electric Dreams last year; ARE very effective at absorbing motor heat during pits between Heats. All you have to do is - after cleaning your tires and braids, --flip your car upside down or, on its side, attach the heat-sink to the motor over the vent hole. To increase cooling, blow on the heat-sink until you need to position it on the track.
These can be purchased at:
Mid America Cooling Magnet
https://www.ebay.com/itm/374481604620 $10
RGEO Heat Sink - Anodized - RGEO-210A
https://e-slotcar.com/rgeo-heat-sink-anodized-rgeo-210a/ $12
