Marco Andretti went fastest on just his eighth lap of the 0.875-mile asphalt tri-oval Iowa Speedway to book his place in the top eight pole shootout qualifying heat later on Friday evening.

He'll be competing in the 30-lap qualifying heat with the likes of Dario Franchitti, Will Power, Scott Dixon, Ryan Briscoe and Helio Castroneves.

However, the best that Rubens Barrchello, Tony Kanaan and Justin Wilson can do now is ninth on the grid; and the best position that Graham Rahal, Oriol Servia or Josef Newgarden can aim for is tenth.

Under the one-off experimental 'heats' format for setting the grid at Iowa this year, practice 2 became a de facto qualifying session, and finishing in the top eight became all important for anyone wanting to start in a decent position on the grid for Saturday night's race. Unlike the usual oval qualifying system, however, there were no one-by-one speed trials - it was a free for all with all cars able to go out on track at any time throughout the 45 minute session.

James Hinchcliffe went top early with an immediately impressive lap of 184.473mph which was finally bettered by Ryan Briscoe seven minutes into the session running 185.383mph, but almost immediately the morning's fastest man - and 2011 race winner - Marco Andretti responded by putting in a blistering 186.041mph lap on his eighth revolution, easily the fastest lap of the day and far in excess of the 2011 pole time of 180.373mph.

Helio Castroneves was on the move in the next phase of runs, leaping up to fifth place and then into second with a lap of 185.713mph next time around, while further back Hinchcliffe had been pushed down the running order by Will Power and Ryan Hunter-Reay muscling into the top five. Alex Tagliani and Tony Kanaan were provisionally in the top eight, with JR Hildebrand and Graham Rahal on the wrong side of the Heat 3 entry line.

After a quiet middle section seeing little change in the running order, the teams and drivers regrouped for the final big push and changing to new sets of red sticker soft compound tyres. Rubens Barrichello was the first to make a big improvement, jumping up to eighth place with seven minutes to go, which signalled a dash for the track for many of the competitors, making it a very busy place to be.

Graham Rahal pushed into the top eight, but Justin Wilson's run landed him on the wrong side of the heat 3 cut-off. Will Power improved to third and Scott Dixon jumped to seventh place as the clock ticked under one minute remaining, but few others could find improvements in their earlier time and ended up returning to pit lane.

One of the few exceptions was Barrichello, back out again and pulling out a lap of 184.591mph that seemed to put him into the top eight again, until just seconds later Dario Franchitti - quite out of nowhere - put himself second fastest overall with a flier of 185.715mph. That bumped Barrichello out of the pole shootout heat and left Franchitti's own Ganassi team mate Scott Dixon hanging on the bubble, but fortunately for the Kiwi it was too late for anyone else to put in a time good enough to displace him.

A big surprise of the session was the form of Takuma Sato, last year's pole sitter, who was struggling to find any pace during the session and spent most of the 45 minutes a second off the top time. He improved on his very last run to just outside half a second of Marco's target time but that was still mired back in 24th place just ahead of HVM's Simona de Silvestro.

But that incident-free 45 minute session still does not finalise any grid position just yet, only which heat they will now take place in. Despite his untouchable time in both practice sessions, Marco Andretti could still end up lining up in eighth place on the grid, while Sato could yet boost himself up to tenth plac eon the grid should bhe win the first of the evening's heats.

Regardless of where they qualify in the heat races, Ganassi's Graham Rahal now joins KV Racing Technology duo Tony Kanaan and EJ Viso in having to serve ten-place starting grid penalties for engine changes.

Each heat race on Friday evening will consist of 30 laps; at the qualifying speeds of around 17.5s per lap, that means that each heat could be complete in under ten minutes if there are no cautions.

Heat 1 Will set positions 10, 12, 14, 16, 18, 20, 22 and 24 on the grid.

1. Graham Rahal
2. Josef Newgarden
3. EJ Viso
4. JR Hildebrand
5. Oriol Servia
6. Mike Conway
7. Ed Carpenter
8. Takuma Sato

Heat 2 Will set positions 9, 11, 13, 15, 17, 19, 21, 23 and 25 on the grid.

1. Rubens Barrichello
2. Alex Tagliani
3. Justin Wilson
4. Tony Kanaan
5. James Jakes
6. Charlie Kimball
7. Simon Pagenaud
8. Katherine Legge
9. Simona de Silvestro

Heat 3 Will set positions 1, 2, 3, 4, 5, 6, 7 and 8 on the grid.

1. Marco Andretti
2. Dario Franchitti
3. Helio Castroneves
4. Will Power
5. Ryan Briscoe
6. James Hinchcliffe
7. Ryan Hunter-Reay
8. Scott Dixon

Full practice 2 times and positions available.