I don't know what you mean about the grooves but a set of underdrives (larger pulleys to run the accessories slower) will free up some HP you already have. All things being equal you'll probably see a few extra ponies to the rear wheels.
__________________
66 Coupe Tahoe Turq - 200, Pertronix & Flamethrower, 3 Row Rad, Cliff. 6/2 96 GT Vert Laser Red - FMS pulleys, Bullet ProM, BBK CAI, Prof. Prod. Elbow and 70mm TB, MAC Off-Road H, Borla side exhaust, Tokicos, B&M Ripper, 18x10 & 18x9 DD Bulletts 06 GT Tungsten, UIP, Red Leather, Stick, 18" blades, Steeda CAI, SCT XCal 2 w/ MC Racing 91 tune, MACs, BMR SP010 springs, BMR Adj Panhard, CDC ducktail & quarter louvers, Rear louver, painted black stripes
they do not ADD any horsepower or torque. they slow down belt driven accessories such as alternator, water pump, oil pump, etc. it is estimated that it FREES UP anywhere from 8-15 hp, but that is because power normally wasted on your accessories is now able to go to the wheels instead. and what do you mean by without grooves?
__________________
2003 Mustang GT, Green Performance Air Filter with stock tubing and air box, Ford Racing 70mm Throttle Body, C&L Trueflow Upper Intake Plenum, Pypes Violator cat back, 3.73 gears, Diablosport Predator Tuner, Tri-ax Shifter, Steeda UDP's, Mach 1 chin spoiler, Mach 1 grille delete, H&R lowering springs, Simco Gauge Cluster, Bullitt pedals
Your not goanna gain HP but the pullies are sized so that the strain that your normal pulleys put on the engine isnt as drastic leading to a more efficient running engine
__________________
BBK 78mm TB/plenum
SCT Tuner Chip 93 Octane Tune
NX 2v Plate kit 100 shot
ngk tr-6 gapped @.035
BBK EL Shortys BBK O/R x Pipe
American thunder series 2 chambers
3.73 gears and CAI Best 1/4 mile 13.43 @104 Not on the bottle
i have steeda udp's and i it made a little difference nothing extreme but they didnt affect any output but they will affect output if you have aftemarket stereos, subs, amps etc..
What if you change the pulleys but not the alt pulley.Will the alt be ok or it does not matter.How much do you loose from the alt when after market pulleys are put on.
under dive pulleys add how much power? 
Best 1/4 mile 13.43 @104 Not on the bottle 
