I've gotten quite embroiled in Firebat arguments over the years. From what I've gathered, the Firebat WILL fly on the stock motor, but only if the motor is one of the stronger ones off the line, and you get everything ABSOLUTELY PERFECT when you build the plane. There is no room for error; get the CG 1/4" off in either direction and the plane will fly as if it is underpowered. Get the weight 1/2 oz too heavy, and the plane will fly as if it is underpowered. It's not underpowered, the plane is simply flying in a very draggy attitude.

Speed 400 can motors are just not known for consistency. There are strong ones, average ones, and ones that don't work worth a crap right out of the box. Problem is, they're not manufactured to exacting tolerances, and not manufactured for airplane use. They're made by the millions for toys, appliances, etc where they're not pushed nearly as hard.

The best advice for a Firebat is to get the basic kit, then either go for lightweight with a GWS EPS350C drive and smaller batteries, or go with something better than a Speed 400, be it a 480, or a brushless motor.