HRT will try a new floor in free practice in Singapore, its biggest upgrade since the Spanish Grand Prix in May.
F1's tail-end team had closed the gap to closest rivals Marussia in the first part of the season, but has slipped back in recent races. It is hoped that this upgrade, once optimized, will again allow HRT to challenge Marussia.
"We have a proper floor now, the most significant upgrade since Barcelona," Karthikeyan said. "To bring it to a street circuit and to make it work straight away, I don't know, because it's pretty bumpy, but hopefully it will be OK.
"It will close the gap to Marussia, but whether we are going to be ahead of not, I don't know. This one race won't tell us because we still have to fine-tune the car. It should go very well in Japan if we get it working."
Karthikeyan expects the new floor to improve the car's stability under braking, as well as the anticipated increase in downforce.
"Overall downforce is what makes you go faster and drag is obviously important, but it will also improve stability under braking," he said. "Our simulations are quite good, but until you drive it, you don't know. We're hoping for a little bit more than a few tenths of a second."
Pedro de la Rosa is set to try the new floor during Friday's first free practice session, with Karthikeyan also running it in the second session after taking over his car from Ma Qing Hua