I have an ST170 and have tried to tune it a little, for a start your lucky if you have anywhere near 170bhp, expect standard power to be around 160bhp maybe as low as 155.
I have a 12lb aluminium lightened fly with kevlar stage 3 clutch, CFM underdrive pullys, CFM exhaust cam gear retarded 8degrees, ported throttle body, dream science map, K&N typoon induction kit and mongoose cat back exhaust system and mine only made 189bhp before the recent cam adjustment. I have spent quite a bit on parts but saved money with fitting and set up as i can do this myself, but even so i feel it was money wasted. Also as a daily runner expect between 20-30mpg if your lucky, mine does 18-22mpg average