Joe Ling, have you actually run a 9XL on 5S in an 1/8 scale vehicle? I know that it looks reasonable on paper, but in practice, it is just way too crazy for the track.

The problem is that when you gear down to attain a certain top speed, there is so much torque that you can't control the vehicle, no matter how careful you are with the throttle. Besides, the added weight of the 5S pack is no benefit on the race track.

I've tried it all. I have a good half a dozen Feigao motors laying around in assorted kv ratings. I've settled on the 9XL with the 4S lipo pack for the track.

At this point, if I had just listened to Glassdoctor, I could have saved myself a whole lot of time and money. Doing the math, my 9XL is only spinning at under 25,000 rpms; but that enough to smoke just about any nitro vehicle on the track, when geared 16/46. At 14/46, I'm just running with the fast nitro pack.