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

Years ago I had a 650 double pumper with the choke horn on my hopped up 360 (this was in Colorado at high altitude). I took it apart and swapped in a 750 Proform main body and the car picked up 3 tenths of a second on the first pass down the 1/4 mile....after tuning I scrubbed another tenth off that....needless to say, I was shocked it picked up so much.