There's undoubtedly differences in 17.5 blinky motors.
Gearing correctly, having the right motor timing for best efficiency/rotor slip, making sure the bearings are aligned and the rotor slides freely between them, light bearing oil, good stator and rotor numbers, and shimming are all important.
Want a good motor? Buy a lot of motors or find someone to get you a good one. You're not going to turn a dud into a stud, but you can polish your turd.
Other options: Run mod or a boosted class.
That said, with 17.5 I run what I've brung and try to make up time as possible in the entry/mid corner.
Team Associated | Reedy | Airtronics
RC Excitement: Fitchburg, MA | RC Madness: Enfield, CT | Horsham RC