Toyota SUPER GT racer Nick Cassidy has labelled Honda's testing pace advantage "scary" ahead of the opening race of the season at Fuji Speedway on 19-20 July.
Honda's new front-engined NSX-GT topped both days of running at last weekend's test, with ex-Formula 2 racer Tadasuke Makino setting the pace on Saturday in the #100 Team Kunimitsu car and Tomoki Nojiri putting the #8 ARTA car on top on Sunday.
Makino ended up with the quickest time of the test, 0.034s faster than TOM'S Toyota newcomer Sacha Fenestraz.
All three Bridgestone-shod Hondas finished in the top five of the test overall, while the Red Bull-liveried Mugen NSX-GT was eighth-fastest and best of the Yokohama runners.
Cassidy's team-mate Ryo Hirakawa set the sixth-fastest time of the test in the #37 GR Supra, and while the 2017 champion was satisfied with the progress made with the all-new car, Cassidy (below) conceded that it was still behind the Hondas.
"We're still slightly behind the NSX but it's pretty close," he told Autosport.
"It seemed Honda could go fastest whenever they wanted, which is kind of scary.
"But I think we've had a good pre-season.
"We've ended much stronger than we started, we've made good progress, so I'm optimistic."
Fenestraz said he felt that the aerodynamic updates Honda brought for the test will make it tough to beat.
"We saw that Honda brought an aero update, with lower downforce, and we saw straight away it was helpful for them," the Japanese Formula 3 champion told Autosport.
"They are going to be up there and will be fighting a lot with them.
"We'll see, but I think Honda are the guys to beat so far from what I've seen.
"They have solved the issues they had in the last test and now they look very strong, maybe at the moment they are quicker than us. So I think we have some work to do."
Cassidy added that with laptimes so close, the success ballast rules could have an even larger effect on the way the season pans out than usual.
For the first six races of the year, every championship point earned in the GT500 class results in 2kg of extra ballast up to a maximum of 50kg, meaning whichever car wins the Fuji opener - worth 20 points - will head into the second round with 40kg of ballast.
Cassidy admitted that he was "worried" that the season will "be dependent on luck and the weight regulations".
"Everyone is so close in performance now, and Honda is now a bit more consistent across their cars [with their drivers]," he said.
"But it means with everyone so close, if you gain 40kg, you'll go from first to 10th.
"If you're heavy and you get a good result, it could make a big difference.
"I think that will be the most important thing, making the best of your weight while you have it."