Ex-Formula 1 racer Kovalainen has finished fifth and ninth alongside teammate Yuichi Nakayama in his two outings of the year so far, after missing the opening two rounds of the season at Fuji due to COVID-19 travel restrictions.
It means SARD's #39 GR Supra is the only Bridgestone-shod Toyota running without a fuel restrictor this weekend at Fuji, although it is carrying 38kg of success ballast.
Kovalainen secured fifth place on the grid in Saturday's qualifying session, a little under a second away from the pole-sitting ARTA Honda NSX-GT of Nirei Fukuzumi.
But the Finn was concerned by the relatively small gap between the SARD Toyota and the championship-contending TOM'S GR Supras, which are running stage two fuel restrictors estimated to cost them around 7km/h in straight line speed.
That gap was just under half a second in practice, and around four tenths in Q1, albeit with SARD progressing to Q2 and both TOM'S cars getting knocked out.
Speaking to Motorsport.com ahead of qualifying, Kovalainen said: "The guys with the restrictors are too close to us. The gap wasn’t enough, it was only half a second to TOM’S [in practice]. It should almost be double that.
"We are missing a little bit, we haven’t got to the bottom of it. The other [Toyota runners] seem to have found more grip, a better balance even. It’s a bit painful, but we are trying.
"We have all the data available from the other Toyotas, we don’t know exactly what they are doing but we can see where they are quicker than us."
Heikki Kovalainen（#39 DENSO KOBELCO SARD GR Supra）