Let's start with complete information. There is no Rimfire 50 motor that I can find.
http://www.electrifly.com/motors/gpmg4505.html
What motor do you have?
There is a Rimfire .55 but that is no where near the power you mention.
There is a Rimfire 1.20 that is 50 mm wide but that is not a Rimfire 50.
There is a Rimfire 50CC that might be what you are talking about.
Manual:
http://manuals.hobbico.com/gpm/gpmg4800-4805-manual.pdf
RimFire 50cc (80-75-230) (GPMG4800)
Motor Output Shaft Size: 10mm
Motor Diameter: 80mm [3.14”]
Motor Can Length: 75mm [3.0”]
Mounting Space Length: 87.3mm [3.44”]
Weight: 1250g [44.1oz]
Input Voltage: 33.3-55.5V (9-15S LiPo)
Max Continuous Current: 110A (at 12S)
Max Continuous Power: 5000W
Max Surge Current: 135A (at 12S)
Max Surge Power: 6500W
Prop Range: 22x8 to 26x10 glow/gas prop
Sport Aircraft Weight: 12.7kg [28lbs] [460oz]
3D Aircraft Weight: 8.17kg [18lbs] [288oz]
Which one do you have?
Assuming it is the Rimfire 50CC, the max specs are shown. Exceed them at your own risk.