What is the best way or thing to buy that increases low-end horsepower(acceleration)

 

You will probably get a few different things you can do to help throttle response and low end acceleration.

Electric fans(reduce parasitic drag of mechanic fan), tuner or chip of some sort, go to a lower gear in the rear end, CAI. If you change gears you will need to have your pcm reflashed for correction of the speedo or you can do it with a tuner or chip. Im sure you will get more input but these are few things. Hope this helps.