The IZOD IndyCar Series continues to fine tune its technical regulations, with further changes to the recently re-introduced "push-to-pass" overtake system in time for this weekend's race at Sonoma Raceway.

The push-to-pass button adds 200rpm of extra turbocharger boost to the power output of the 2012 specification 2.2-litre V6 engines to make overtaking moves possible on street and road course circuits, in a rough equivalent to the DRS or KERS boost seen in F1.

However, officials were disappointed when its main use at Edmonton was by race leader Helio Castoneves using it to hold off Takuma Sato in the last 15 laps of the race. Castroneves was able to deploy the system at the direction of his pit crew who could see real-time information about other competitors using push-to-pass from the live TV feed and timing and scoring system.

As a result, for the following race at Mid-Ohio the series introduced a five second delay between the pressing of the button and the power coming online, which meant that it couldn't be used fast enough in response to other cars attacking from behind and was only effective in planning overtaking moves in advance on cars in front.

After analysing the racing action from that race, IndyCar has now trimmed the activation delay down to 3.5 seconds for this weekend's GoPro Indy Grand Prix of Sonoma. The series also confirmed that drivers will have a total boost time of 90 seconds available to them for the duration of the race, in bursts no longer than 15 seconds in duration.

"All parameters of the push-to-pass system can be tailored to fit any circuit that play host to IZOD IndyCar Series races," explained IndyCar's director of engine development, Trevor Knowles. "Sonoma has shorter straightaways than what we had at Mid-Ohio, so we've adjusted the parameters of push-to-pass to fit this particular circuit. But the principles for use that were in place for Mid-Ohio have remained the same for Sonoma."

The series has opted not to introduce a recharge time between uses of the push-to-pass system at this stage. The system will be used only once more in 2012, at the following week's race in Baltimore, and will not feature in the mid-September series finale on the Auto Club Speedway oval course in Fontana, California.

Teams were able to test the tweaked power boost settings at the end of last week in their one day open test at Sonoma. Drivers used the time to get used to the revised layout of the track, formerly known as Infineon Raceway and before that as Sears Point Raceway.

The run down to the hairpin turn 11 has been lengthened by 200 feet to make a deeper turn, giving drivers more opportunity to out-brake their competitors and to get a better run out of the turn and set up a pass into turn 12. The exit from the Bus Stop (turn 9) has be widened, and turn 7 has been remodelled into a new hairpin. The changes make the circuit into a 12-turn, 2.31-mile road event.

The drivers seemed largely happy with the changes to the track after their first taste of it last Friday.

"It's just three new corners and it's actually quite different," said Ganassi driver Dario Franchitti. "It was almost like learning a new track."

"I think the track is definitely going to promote more passing in turn 7," speculated Will Power. "The passing zone in 7 is the best one, but if they changed turn 11 to modify the exit curbs a bit it could be good, as well," the Penske driver added. "But good changes, for sure."

"So far it seems really good," said Dale Coyne Racing's Justin Wilson. "It allows the track to drive better and the chicane is a big improvement. It's still going to tough to overtake, but turn 7 is a lot better. Down in turn 11, it's going to be a lot of slipping and sliding. It's tough, but I like it a lot."

"Opening up the turn 9 chicane is definitely a move in the right direction," agreed JR Hildebrand. "I give the track a lot credit for making the changes and trying to adjust."

However, the Panther Racing driver pointed out that, "A lot of the moves were done to help the passing, but until running side-by-side it's hard to tell if it's really going to be effective." He added: "We'll see as we continue to run how it all pans out."

20 drivers in total attended the test day. Official lap times were not recorded, but other sources suggested that Power, Castroneves and Ganassi's Scott Dixon all reached best times of around 1:19.1s.

Drivers will also have the opportunity to take part in extra practice at the course on Friday, when 27 drivers will be in action including Sebastian Saavedra in an AFS Racing/Andretti Autosport co-entry and Katherine Legge in a second Dragon Racing car, her first road course outing since Sao Paulo, Brazil in April.

Charlie Kimball will also be back in action this weekend in the #83 NovoLog Flex Pen Ganassi Racing car, after being forced to sit out Mid-Ohio following injuries to his hand in a practice crash during July. His place in the race had been taken by former GP2 champion Giorgio Pantano.

"It's good to be back in the car," said Kimball, after running in the August 17 test at Sonoma following his all-clear to return to the cockpit from IndyCar's medical director Dr Michael Olinger. "I think it will ache later tonight. All in all, the doctors cleared me on Wednesday and we made some braces."