Hey Rick, I'm gonna try to explain it from what I understand.......lol
Jump in here if I'm wrong Nick!!!!
The Copperheads come in 3 different combos. The only one that comes with the Copperhead esc is the 3900kv motor combo. The 4500 and 5150 come with the Copperhead-R esc.
Here's the differences:
Viper Copperhead
Continues/Burst Current:100A/550A
BEC Output:6V/5A Linear
ON Resistance:0.0009Ω * 2
Support Motor Type:Sensorless Brushless Motors
Support Motor Spec
2S Li-Po w/ 540 class: KV ≤ 6000
3S Li-Po w/ 540 class: KV ≤ 4000
Support Vehicle Weight: ≤6 lb
Motor Connection:3.5mm Bullets
Dimensions:45.5x39.8x29.25mm
Weight (with battery wires and connector): 96g
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Viper Copperhead-R
Continues/Burst Current:150A/750A
BEC Output:6V/5A Linear
ON Resistance:0.0005Ω * 2
Support Motor Type:Sensorless Brushless Motors
Support Motor Spec
2S Li-Po w/ 550 class: KV≤6000
3S Li-Po w/ 550 class: KV≤4000
Support Vehicle Weight: ≥6 lb
Motor Connection:4.0mm Bullets
Dimensions:45.5x39.8x29.25mm
Weight (with battery wires and connector): 98g
Basically, from what all of this info tells me, it says don't put the Copperhead into a Losi SCTE!!!! You better use the Copperhead R...... and it has a cool looking little R on the speedo too. I think just the R on it makes it faster!!!! Gotta say that the Copperheads are some of the best looking esc's out there. Very pretty.
Here's the link from where I copied and pasted all this from:
http://www.viper-rc.com/vx4.html