Bobman 3 blade 11x7 or 11x8 MAS I went Super Tigre for 3 reasons. 1 Top Flite thought it was good enough to make a special exhaust system for P40 and Spit. 2 fantastic price. 3 I read a RC magizine article about the ST 61 and 75 in a spitfire ,that the sound was perfect of the merlin and allison engine winding up and down. I've never heard a real merlin wind up or down so I had to take his word for it. I've heard the big allison ww2 engines in up close in tractor pulls ,but with special exhaust it couldn't be the same. Plus ST lasts a long time and is easier to start than those super tight TOWER 75 which I have 2