When assisting others with reasons their cars seem slow, these are the top things I see which pop up many times as the main reason for the performance issue.
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Keep your battery/motor connectors in perfect condition, whether they are plugs or bullet connectors. Replace them often.
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Make sure you have 'bright' looking solder connections. A bright solder connection indicates proper heat was applied and 'flowed' throughout the attachment point, making a low resistance connection.
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At plug type connections, make sure they are inserted to the full depth to make sure of a good continuity, especially the sensor cable from ESC to motor.
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In addition to the battery/ESC connections, look at the sensor cable between the motor and ESC. Replace it often, have spares in your tool box.
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Do not let wires 'flop' around. This will cause intermittent issues, which are hard to find. Secure the wires with tie-wraps to the chassis. The cable between the receiver and the ESC is especially critical, will cause a host of problems.
Have a great race season!