Freeman (22), a wheel alignment technician, won the 28-lap race on his home track in 12min 20sec from Damon Leitch (Invercargill) in 12min 45sec. Kerry Bowen (Dunedin) was two laps behind in third place.
But it would not have happened without the assistance of Ramsay, who took the engine out of his own kart and drove south from Christchurch on the night before the race.
It was inserted into Freeman's Tony kart, which is powered by a Vortex engine from Italy.
Freeman had gearbox problems when he raced in his heat of the KZ2 on the Saturday and finished fourth in the final with the help of a borrowed engine.
Freeman had a more powerful engine when he raced in the open event on Sunday.
He started impressively when he broke the record for the 550m track at the bottom of Three Mile Hill in 24.79sec. But a lap later, Chris Cox (Christchurch) lowered it to 24.77sec.
Cox was leading the final when he had engine problems and pulled out with four laps left. It was Freeman's first open title at the South Island championships. He had won the senior light-class title in 2007.
Freeman followed father Warwick, uncle Tony and cousin Regan into the sport as a 6-year old.
He enjoyed the challenge of driving the open class karts that have brakes, gearboxes and more horsepower.
"There is more to think about," he said.
"My Tony kart has 49 horsepower, a six-speed gearbox and can accelerate from zero to 100kmh in 2.9sec.
"We reached speeds of 130kmh at the nationals but on bigger tracks we can reach 160kmh.
"These karts have the same grip level of a Formula One car, which is why Formula One drivers still use them for training."
Freeman's best national championship performance in the open class was his seventh place in Invercargill two years ago. He hopes to go better in Wellington at Easter next year.
