If you are looking to upgrade a Madrat to brushless make sure you buy a full set of ballraces for the car or it will go up in smoke soon.
If you are thinking of the 5.5 combo that is available for peanuts on ebay and has a motor with cooling fins steer well clear of this if you are thinking of ever racing the car. Much better to stick to some of the slightly more expensive kit from one of the major brands. If it's for bashing about the park go for it.
You will need to adjust the gearing but just check the Ansmann section of the forum. You will be bound to find some information on how to gear what motor.
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