Remind me again why the transmission was invented? That's right, to multiply usable torque beyond what the engine produces. Torque is multiplied through gearing, horsepower is not. Read this:
Horsepower vs torque
14.5 at the engine * 7.1:1 gearing= 103 pounds output. See? There was no mathematical wizardly involved here. PhD not required.
Want to see it again? My truck outputs 360ft/lbs at the crank. First gear is 2.7:1. The rear axle ratio is 3.73:1. 360*2.7*3.73 equals about 3700lbs of torque, or roughly double that if low range is engaged at the engine's peak torque of about 2600 RPM. This isn't difficult people. If you really wanted to get technical you could deduct losses through the transmission, rotating mass of the driveshaft, ect.
Sorry about your Nissan...it must suck to have a car that can't even put 100lbs to the ground. My streetbike (Yamaha Vmax) puts 113 to the ground at the rear tire, and that weighs 500lbs. It also does 60 in 2.9 seconds.
Do you need to push going up hills?
Anyway, try putting an even 1:1 gear ratio on your bike, and let me know how well it does going up a hill, if it even gets moving at all. That will tell you how far 8lbs of torque from a clone motor gets you.
Hell, how well does a stock doodlebug do with an adult on board? I can't imaging that 97cc putting out much more than 3-4lbs of torque, on a what, 6:1 ratio? 24lbs of torque being optimistic? That doesn't get your far, now does it?