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

Can think of two things over the years i changed that made a lot more difference than i would have thought before doing them

1. swapping from an 8 to a 10 inch rear wheel… 10 inch slick
Couldn't believe how much more stable the car was going down the track(9 sec car). Huge difference. Drove like a Caddy compared to 8 inch wheel

2. completely removing 50 year old wire and installing all new aftermarket wiring system.
Car starts way better, battery stays topped up, never needs a battery charger, just night and day difference. And under the hood WAY cleaner look.


What are things you guys have done?