It calls for up to a .91 FS... What is the size difference in the 91 and the 120? Just compare them...

O.S. 120
Weight: 920g (32.5oz
Length: 102mm (4.09") from backplate to the front of the drive washer
Width: 47mm (1.85") width of engine neglecting the mounting flanges
58mm (2.28") distance between the mounting hole centersh
Height: 139.5mm (5.49")
Suggested Prop(s): 14X9, 14X10, 14X11, 15X8, 15X9, 15X10, 16X6

O.S. 91
Weight: w/o muffler - 22.2 oz (630g) with muffler - 23.9 oz (678g)
Length: 91.5mm (3.60") from backplate to front of drive washer.
Width: 42.6mm (1.68") width of engine neglecting the mounting flanges
52mm (2.05") distance between the centers of the mounting holes
Height: 123mm (4.88")
Suggested Prop(s): Stunt planes: 11X10, 11X11, 12X9.5, 12X10, 12X11
Scale models: 13.5X8, 14X7, 15X6, 16X6, (12X8 & 12.5X7-3 blade)