I had two cars that I put an underdrive crank pulley on and honestly felt nothing. However on my Mustang GT V8 and most recently my G8 GT V8 I most definitely noticed quite a difference, especially the G8. It became much more responsive, had a better kick in the last 2,000 rpm before red line and most noticeable it revved towards red line much much quicker. These were V8's I noticed the big difference. Is there such a thing for the V6 SHO? Is it worth doing? Any input appreciated.
I wouldn't. I had one on my daily driver Marauder. HATED IT. Had to make the car idle higher 800 vs 650 and even then in the winter at a stop light with the heater/defrost on or summer with AC/headlights on my voltage would drop badly. It also slows down the water pump. So think about idle in 100* heat, your water pump is moving slower, and your electric fan can't get the juice it needs with the AC on too... Then you overheat in traffic.
On the dyno I picked up 5rwhp. It wasn't worth the headache of what I mentioned above.
I had similar issues in my first 2 efforts, but they were a kit, with water pump pulley, alternator and crank pulley. Ended up using only the ctank pulley and 3 sets of belts, not cheap. G8 no issues at all, just uses the crank pulley and added 50 rpm to idle only slightly dimmed lights with AC and defroster on. Was never a problem and performance was well above its pay scale
I am not aware of an underdrive pulley for the ecoboost, and IMO would not mess with it.