Things you did/upgraded that surprised you how helpful they were

Years ago I broke one of my 340s and had a 318 that I picked up from a friend it ran 13.20s with a 3.91 gear and a 10 inch converter, put in an 8 inch converter and starting going 12.70s.... my pickup runs low 15s with 60 fts in the 2.20s I sent my stock lockup converter to Lenny at Ultimate he redid it now it goes 2.00s in 60 ft... last year I had the car totally rewired by Mike at H.P. Motors and added a one wire alternator after years of not starting, spliced in accessories and not charging it now starts every time and charges at 14 volts constantly