Well, I would say about 15 of the top 20 cars here locally on the dirt are running the Dart's... I picked up a used set from one of them last winter and put them on a buddy's sbc in a '70 chebbie pickup.... Result was an increase in horsepower that you could tell without using a dyno! I would say an easy 20 to 25 horse better then the stockers he had on it. Engine is one of the cheap crate motors from Chevy. Heads made a HUGE improvement!