Have you tried second curtain flash? This fires the flash just when the shutter is about to close allowing for the car to render a little sharper with a blur behind to accentuate the motion.
More light will also help, moving the toy closer to a window can improve your shooting environment.
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~ Newt ~
Canon 5D MkII | Canon 40D | Canon A2 | Canon F-1
EF 16-35mm f/2.8L | EF 24-70mm f/2.8L | EF 70-200mm f/2.8L IS
EF 35mm f/1.4L | EF 50mm f/1.4 | EF 85mm f/1.8 | EF 300mm f/2.8L IS
EF-S 60mm f/2.8 MACRO | EF 100mm f/2.8 MACRO
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