Indonesia's Haryanto, who is set for a momentous first day behind the wheel on Wednesday, said improvements were notable even from the sidelines - and that he therefore cannot wait to make his first appearance as a Formula One driver.
"You can see the step we made from yesterday to today is already quite huge," he commented, "and there is still more to come.
"The lap times were 1m 28s on day one and 1m 25s on day two - that shows just what potential we have to improve. I can't wait to get in the car.
"I think Manor have a good package this year - we've had two successful days with good reliability. I learned a lot from listening to Pascal in the car - and now I'm looking forward to getting track time myself!"
Wehrlein, who comes into F1 racing on the back of a historic championship triumph for Mercedes in DTM, is also convinced of Manor's underlying potential.
"Another good day in the car for me," he explained, having racked up 71 laps and finished eighth fastest overall. "I'm pretty pleased with our performance.
"We focused on consistency rather than the softer spectrum tyres, so we have yet to evaluate the car on the supersofts and ultrasofts, which means there is more to come. We're making good progress and I can't wait to get back in the car next week."
