Here is some info from Brian's motor selector program...I wasn't sure what diff gear ratios are in the 8ight so I used 43/13. I also assumed you'd be running 4S and want to be in the 45mph range. I input values using a 15T pinion and 47T spur. You may want to go a little smaller on the pinion. Ideally you want the motor rpm to stay at or under 40K...I guess it doesn't hurt to push it a little over that every now and then

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Vehicle Weight (approx): 10
Desired top speed in MPH: 45
Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Additional Ratio: 1
Spur Tooth Count: 47
Pinion Tooth Count: 15
Battery Voltage: 14.8
Tire Diameter (inches): 4.1
Total Ratio: 10.3641 : 1
Tire Circumference: 12.881 inches (327.165 mm)
Required Motor RPM: 38236.172 RPM
Required Motor KV: 2583.525 RPM/V
Good Motor Choices: 7 XL (kv=2382)
6 XL (kv=2779)
Better Motor Choices: No motors of this class fit the parameters you entered.
Best Motor Choices: 1515 1.5d (kv=2700)
1515 1y (kv=2200)
1512 1y (kv=2750)
1512 2d (kv=2550)
LMT 1940/7 (kv=2239)
LMT 1940/6 (kv=2613)
1521 1d (kv=2900)