Maungakaramea's Riana Phillips, 16, and Kerikeri's Imogen Hull, 14, make up half of the relay team attempting to break the record of four minutes 17.77 seconds.
The Northland record was set two years ago and, at the time, was the fastest 4x400m age group relay time nationwide that year with Riana part of the foursome that created it.
Portch expects the record will fall next Tuesday when the girls have their shot at it.
"The reason why I'm confident in this case is because we will run different age groups together in the championship, men and women, which will provide them with competition."
He says there is a lack of competition in Northland to push Phillips and Hull individually, but for the relay there is good competition when age groups are combined.
Phillips agrees breaking the record is highly possible thanks to her improvements during the past two years.
"This year, it's about trying to drop the time right down because since the last record I've dropped my time by about three seconds."
The Tauraroa Area School student said her ultimate goal is to run the 400m in 58 seconds, which would rank her second in her age group nationally.
Portch says the difficultly with Phillips is she has only been racing the 400m seriously for about 12 months, previously specialising in the high jump where she ranked consistently in the top 10 nationally of her age group.
Hull said beating the record as a team would be a different feeling considering athletics was usually an individual sport.
"She's [Phillips] fast. Because she's so fast it means we can take a little bit longer. [But] I think we will beat it."
Portch hopes the girls can do enough in the coming months to be considered for the Oceania Championships in Cairns later this year.
