Mr Williamson will know for sure after the seven-race Central Rivers series on March 2 and 3, when he will go head to head with John Derry, of Blenheim, who has also made the switch to helicopter-style gas turbine power.
Mr Williamson demonstrated his boat for the Otago Daily Times on the Frankton Arm of Lake Wakatipu and the Kawarau River recently.
Two things impressed immediately. One was the sound - more the swish of water on the boat's hull than engine noise. And the other was the smell of kerosene as it passed.
His new 1400hp engine is a General Electric T58 out of an American Sea Sprite helicopter used by the military and for heavy lifting - but also used in the helicopter that flies US President Barack Obama.
Mr Williamson bought the engine after having reliability issues with previous big block engines, and with an eye towards the world jet-boating championships being held in New Zealand in October.
''This will sort of get us up with some of the fastest boats in the world, really.''
It has taken Mr Williamson 18 months to get the boat ready for its first race and he says it is performing well.
''There's a big initial setup cost to put them together, but your maintenance side of it is pretty much not there.''
Mr Williamson said it was easy to misjudge the boat's speed and more than 160kmh could seem like 90kmh.
He was reluctant to say how much he had spent on the boat.
''You can't ask me that. It's a bit like asking the age of a young lady, isn't it?''The Central Rivers series begins on Saturday, March 2, on the Dart River and moves to the Matukituki and Clutha Rivers near Wanaka on Sunday, March 3, finishing at Cromwell.
The boats start at minute intervals.
The world championships are run on the same rivers in October, and while Mr Williamson said other jet-boat racers were looking at gas turbine engines, they would not have time to get them running before the world champs.