Andre Lotterer on Friday boasted that his Formula Nippon single seater is faster than the F1 cars produced by F1 backmakers Virgin and HRT.
The 29-year-old German, who is leading the Japanese championship ahead of former Williams driver Kazuki Nakajima, won the series' Suzuka round in May.
"Theoretically, if I would have entered today's first free practice with my Formula Nippon, I would be nineteenth," Lotterer, a Jaguar test driver in 2002, said at Suzuka.
In May, Suzuka pole sitter Naoki Yamamoto's Honda-powered Nippon qualified with a time of 1.40.470, which was faster than any Virgin or HRT driver could manage on Friday morning at the same Japanese circuit.
And that Formula Nippon time is just half a second behind Friday morning's slowest Team Lotus runner Karun Chandhok.
The 2011 Formula Nippon single seaters are built by American manufacturer Swift and powered by 3.4 litre V8 engines supplied by Toyota or Honda.