There is a lot of low cost things you can do. It used to be easier, as there was more stuff in junk yards, and swap meets at affordable prices. I used to get a lot of bargins from ebay, but not so much now. I built my whole 66 Valiant drag car for $1500 (including the car), and the first weekend out it was going high 13's in the 1/4. Most of my engines are bone stock short blocks, with a cam/kit, milled head, sometimes big valves, free flowing exhaust, more then stock carb (depends on the bargain), good ignition system. Last but not least POWER ADDER.
