Robin
I too don't know what a MAS500 is but I'll assume that Chas is correct – I've not caught him out yet!
I have brushless installations in my Huntsman and Huntress models, which are 24" long. One of these comprises of a Leopard motor **LINK**
a 30A speed controller (Fwd+Rev) **LINK**
a PropShop 1315 Standard Scale 3-blade RH bronze prop **LINK**
and a 3S 2600maH LiPo battery pack **LINK**
I think this would be a pretty good place to start. You might find that a smaller racing prop and/or a slightly faster motor would increase the speed but with a long thin MTB you have to beware of torque roll. I've had to restrict top speed on this Huntsman to 80% of full throttle as it really does fly!
