He's traded the big block engine for a twin turbo and if Canterbury's Peter Caughey flinches at Hastings then Whanganui's Rob Coley is determined to be right there to capitalise during round four of the Altherm Window Systems New Zealand Jetsprint Championships.

The circus of water speed moves to Riverside Jet Track on Sunday with Caughey holding a 12-point lead over Coley in the Mouthfresh Superboats class after the events at Waitara two weeks ago, where the Whanganui racer first used his new Nissan engine package.

Coley had set down the fastest time of the day heading into the final Top 3 eliminator with 40.8s lap, but a lapse on the Waitara course's hairpin slowed him up, and then multiple time champion Caughey drove a rapid 40.3s lap to win the round and extend his season points advantage.

As a previous runnerup to Caughey in the national series by just one point, as well as finishing second in the Australian national series over that same 2015-16 timeframe, Coley had put a lot of frustrating time and resources into his big block engine unit, which was ultimately "going backwards".

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Waiata was the first test of the twin turbo and the Whanganui racer adapted quickly, having added a 9-inch intake and doing development of the jet unit.

Coley joked that while the engine roar doesn't sound the same, at least he can talk to the boat crew standing beside the craft, rather than having to yell into each other's ear to be heard.

"As far as the boat was – loving it," he said.

"It just seems an overall package.

"We've got a few more things we may change for the world's [series]."

Coley's 2018 plans have taken a dent as the national series added on an extra round in Waitara after the original second round at Tauherenikau Racecourse was called off due to dry conditions in December.

It created a scheduling conflict after he hoped to enter five of the six rounds that make up the Australian series, thereby being able to contend for the title while getting valuable preparation for the World Series, which will also be held in Australia.

"If I can get dispensation, which they won't give me, I would have packed up and gone.

"They allow you to drop a round, but unfortunately Griffith [Lake Wyangan] is compulsory, because a lot of people were skipping it."

Therefore, Coley will have to wait to June to join the Australian series and will only be able to compete at four rounds.

Looking ahead to Hastings, Coley is well aware that he needs Caughey to make a big mistake or have significant engine trouble in order to make up ground on the 12 point spread.

"I would certainly like to win the title by winning [racing], and I think we can.

"I don't think it will be this year.

"If we take the three [remaining rounds], we're still not there unless something happens.

"I could have been close, could have had him in Waitara."

Still, Whanganui's own Pat Dillon claimed his only NZ1 title in the 2014-15 season when Caughey was dogged by engine problems and a crash in the early rounds of the campaign, showing that anything can happen in motor racing.

"These packages are known to be bombs at times - you push them to the limit," said Coley.

"Hopefully we can be the one to put the pressure there."

Rotorua's Nick Berryman sits two points further back in third overall, while Hamilton's Sam Newdick is fourth and Whanganui's Richard Murray rounds out the Top 5.

After the tight and technical track at Waitara, Coley is looking forward to the Hawke's Bay round, given Riverside with its 24 rotations flows nicely, the hairpin aside, and suits the big engine boats.

"We'll put the gumboot into it."

In the other classes, Whanganui's Ross Travers is third in the Fowler Homes Group A, but similar to Coley is 11 points behind dominant defending champion Ollie Silverton of Hamilton, with Canterbury's Simon Gibbon in second.

The Stinger Boats Group B leader is Te Awamutu's Patrick Haden, having moved ahead of Taranaki's Daniel Reade, while expat Whanganui racer Kellie Minnell is third.

Whanganui's Hayden Wilson sits in fifth place overall.