CRT Setup
 

I setting a CRT up with a Polyquest 4s and/or 5s 6000 mah battery, Neu 1515 1.5Y/F motor, monster max esc, 48t spur, and 18t pinion. What do you think about this setup?

I think you'd definitely be overgeared at 18:48. That gives you a final drive ratio of 8.8:1, which is way too low for a truggy.

What do you recommend? I thought it was better to run a lower kv motor and gear up. I thought this would help things run cooler.

It may help in some situations, but that gearing is too much for that motor IMO. In my CRT, I run 4S on a Neu 1515/1Y geared 13:62, which is right about 36mph. I'm about to jump up to 15:62, but with the temps I have (motor and ESC under 130F) I don't think I'll have any issues. If you want something that will run well on 4S, I wouldn't run anything lower than the 1515/2.5D (1650kv). If you went with that motor, I'd probably start with the gearing somewhere around 18:62, which should get you into the 37-38mph range.

yeah I also run 13/62 on my CRT, but im running the 2.5d on 5s.(brings about the same rpm as the 1y on 4s) it runs cool and the speed is just about right. I used to have a revo that pulled up 43 on he speed calculator and it felt way to fast, so I would definately aim for something in the high 30s at MAX.

I'm running 15t pinion with a 1600kv Medusa on 5s in my X2 CRT.
About 40mph , heaps of torque and out runs the nitros on the top end at the track , big track by the way .
No heat issues at all .