Scott Dixon became the first driver in either test group to dip under the 52s mark at Sebring International Raceway this week, with the Ganassi-Honda driver setting a best time of 51.7932s (116.077mph) in the morning that was eight tenths clear of AJ Foyt Racing's Mike Conway (also running a Honda engine) in second place.

"Our car right out of the box was pretty decent," said Dixon. "I looked down at my dash and though there was an error, honestly, because it came pretty easy.

That makes Dixon the fastest man of the week, with the best time of the first group of ten cars that tested on Monday and Tuesday being Helio Castroneves with a lap of 52.1413s on the second day.

However, the times on the 1.67-mile, 11-turn short course are not directly comparable, and Dixon subsequently tweeted to Ryan Hunter-Reay (the fastest driver in Monday's session) that "[I] think you guys laid down some good rubber," which had improved grip for the cars running later in the week.

"We're not really trying to go fast at Sebring, but are trying to cover all the bases before we get to St. Pete," he insisted.

Dixon repeated his sub-52s feat again in the afternoon, although the rest of the field had by now closed up on him - led by Dixon's own Ganassi team mate Dario Franchitti, who lost time in the morning session while his car was fitted out with Dallara's modification package to allow the Scot to stick with right-foot braking. A further unspecified issue meant that he only got five laps in during the morning, but he was able to complete 32 laps in the afternoon.

"The first session was a wash out really," admitted Franchitti. "I think I did some out laps and the most I did was two together. It was nice to get this afternoon and see where we were - it's not bad.

"There are so many things we're trying to change, it's not about shooting the car for the track, it's about learning and getting data," he continued. "The difference being, with the old car we pretty much knew what we were going to do."

Rubens Barrichello proved in good form in his first IndyCar open test, running sixth fastest in the morning but then popping up to third fastest for the day during the afternoon session with a time of 52.6745s (114.135mph) just 0.0644s off Dario's fastest effort of the day.

"I'm still a boy playing with a toy, finding out what the toy is capable of giving you," said Barrichello, who was happy to be back on a track that he'd already tested on a month previously. He pipped Conway for the third spot by a slender 0.002s margin to post the fastest lap of the day by a Chevrolet runner.

Asked to compare the relative standings of Honda and Chevrolet engines, Barrichello understandably hedged: "I feel it is really difficult [to tell] until we get to the St. Pete qualifying and race to know where everyone is," he said sensibly.

But he was definitely impressed with Dixon's benchmark laptimes. "The time that Scott set this morning was really fast. It was out of the box. It was really, really fast. Faster than anybody around here from the past week and this week," he acknowledged, adding: "The Team Penske and Target Ganassi are the cars to beat."

Barrichello's new KV Racing team mate EJ Viso was the only driver to have an off in the morning session, causing the session to be red flagged while marshalls reset the tyre barrier. Viso was able to continue testing after he was returned to pit lane and had his front nose replaced, even if presence of the unpainted spare part rather ruined the overall aesthetic of the shiny new livery.

Further back down the timesheets, Ed Carpenter struggled with a misfire problem in his #20 Ed Carpenter Racing-Chevrolet car in the morning that put him well off the pace and behind in his development testing in the afternoon, leaving him further down the times than might be expected for the winner of the final 2011 race of the season at Kentucky.

Sarah Fisher Hartman Racing's Indy Lights rookie transfer Josef Newgarden was also out on track, after the team worked late into the night on Wednesday fitting their brand new Honda engine donated from Bobby Rahal's second car operation. Unfortunately a problem with the car's timing transponder left him with no recorded lap times for the morning session.

There was good news for Lotus Dragon Racing, whose engine arrived on Wednesday and was installed overnight into the chassis and was ready to go out on track shortly after lunchtime. Katherine Legge was able to put the car and engine through 66 laps of running before the end of the day.

"It was awesome to be honest," said Legge. "I obviously have to thank my crew because they worked all the way through the night and all the way through the day today to get me on the track," she added, referring to the all-nighter as a "team-building experience."

Certainly it seemed to have done the trick in breaking the ice: "It feels like home and where I belong," she said of Lotus Dragon. "The team that Jay [Penske] has built this year is incredible, and it's great to have Sebastien's feedback as well."

With only one engine delivered and installed, her team mate Sebastien Bourdais did not run in his own car today and is expected to take over the running of Legge's #6 at some point to get some track time on Friday. But at least Bourdais has already had some recent experience back in US open wheel racing, running a road and street course-only season in 2012 with Dale Coyne Racing. For Legge, it's been somewhat longer.

"It was a little bit alien getting back in an IndyCar after four or five years, and not having raced anything in more than a year now," she admitted. "It took me 40 laps or so just to feel comfortable again, but we did a lot of laps this afternoon and I'm very happy with the way it's progressing."

Brazilian driver Ana Beatriz also got some track time on Thursday, taking over James Hinchcliffe's Autosport car for one day in expectation of her picking up a one-off ride at Sao Paulo in April.

"It was fun to drive the new car today. It has a lot of grip and I'm still learning about it," said Beatriz, who raced alongside Justin Wilson at Dreyer & Reinbold in 2011 but does not currently have a full-season deal for 2012. "It was a great test with Andretti Autosport. I learned a lot today and it will be a great experience to take into the future."

Missing out in the afternoon was Bryan Herta Autosport's Alex Tagliani. After running a respectable 37 laps in the morning, his Lotus engine developed a throttle problem over lunch. Because of the new drive-by-wire systems involved, it took a long time to track down and resolve the glitch. However, team boss Bryan Herta was confident that Tagliani's car would be ready and able to take to the track first thing on Friday for the second and final day of the open test.

Full Sebring day 1 times for the second group available.