For the PA-28-xxx series of aircraft the xxx indicates HP I believe. The original was the PA-28-141 Cherokee, then the -151 and -161. Don't think there was ever a -171. Piper's best offering back in the late 60s was a PA-28-181 Cherokee. The modern day Archer is simply a descendent of that. It's basically a faster Warrior thats all.
The Archer has between 100-200 more BHP than a standard Warrior. Typically achieves a 10KTS faster cruise TAS probably aided by wheel fairings that the Warrior doesn't have.