Just picked up a speed3, just want to see which upgrade I should start with. Any quick fixes for additional HP? Does having the traction control on decrease the power?

 

buy the mazdaspeed intake system.
yes on that vehicle turning off the DSC/TCS will override the boost and timing maps in the pcm
but that additional power in the lower gears will be wasted by wheelspin
1st and 2nd gears are restricted to prevent excess wheelspin.
the speed 3 is a blast to drive. enjoy!!