I recently bought a P-51 Mustang from a sale and it has a Webra 40 on it. Runs good but I would like to know which 40 it is. As far as I can see they make a 40 sport and a 40 GT, does any one know how to tell the difference. And also I think the prop, a 10-6, might be too small for it. This little thing sounds like my boys car motor revving up and I feel like it is over revving. Down loads of the manual are a little vague and cover all Webra engines as a whole. Thanks in advance for ya'lls help.