By DAVE SKRETTA

AP Sports Writer

INDIANAPOLIS — Helio Castroneves felt an immediate difference — a subtle but noticeable uptick in speed — the first time he utilized the boost of horsepower offered by IndyCar’s novel hybrid engines around the imposing oval of Indianapolis Motor Speedway.

The question now facing the four-time Indianapolis 500 winner, along with the rest of the drivers on the 33-car starting grid for the 109th running on Sunday, is how best to capitalize on the hybrid over 200 laps spent entirely on edge.

Empty it entirely and then wait for it to recharge, which might take several laps? Save it for short bursts for passes or to defend? Perhaps use it slowly to run down the leader or build a big advantage once out front?

“There is so much more that goes into this than I think people realize or recognize,” acknowledged Indy 500 veteran Graham Rahal, whose father Bobby Rahal won the 1986 race. “It’s an interesting thing. I mean, the hybrid, it’s quite powerful here. On a single lap if you utilize it correctly, it does make a hell of a difference in lap time or lap speed.”

The genesis of the hybridization began years ago, when IndyCar manufacturers Chevrolet and Honda wanted to better align their racing programs with a shift in consumer demand toward hybrid and electric vehicles. But the project was beset by delays as engineers struggled to fit a bespoke hybrid unit into the IndyCar chassis designed more than a decade ago, and that had to meet certain requirements for weight and safety, among other things.

The result was finally unveiled before last year’s Indy 500, a design based around ultracapacitors rather than heavy batteries. It provides a quick boost to the existing 2.2liter, twin-turbocharged V-6 engines before recharging to be used again.

The system was introduced at Mid-Ohio midway through last year’s IndyCar season and has been in use ever since.

But it has never been used somewhere like Indianapolis Motor Speedway, where speeds at the end of each straight can hit 240 mph, and the difference between winning and losing can be measured in thousandths of a second.

“I’ve had some really interesting conversations with drivers about how of all places where the hybrid is going to make a huge difference, it’s going to be at Indianapolis,” IndyCar president Doug Boles said. “I asked why and they say, ‘Well, you think about Indianapolis, how trimmed out we are — especially in qualifying — any incremental difference in horsepower makes a difference.

“We’re going to see some exciting racing,” Boles continued, “and the strategies that I have heard from drivers in terms of talking about how to deploy the hybrid vary wildly. It’s going to be fascinating to watch how this goes.”

It hasn’t gone without its share of problems, either, dating to an open test last month and right through practice Monday.

For one thing, the hybrid still checks in at about 100 pounds, which is significant on a car that weighs just 1,600. And all of that weight is in the back of the car, which has dramatically altered the way they are balanced and ultimately perform.

“That’s a lot of mass percentage-wise you are adding,” two-time defending Indy 500 winner Josef Newgarden said. “It’s almost like adding 200, 250 pounds to a stock car. If you said, ‘Hey, guys, we’re going to bolt 250 pounds to these stock cars, see what you think,’ I bet they would all go, ‘OK, this drives differently.’ And now we have to counteract it.”

Andretti Global driver Kyle Kirkwood is among many who believe the additional weight makes cars harder to drive, and Meyer Shank Racing’s Marcus Armstrong said, “I do believe the window is considerably smaller, the balance window.”

Armstrong crashed in practice last Saturday and had to squeeze into the field in a backup car on Sunday.

Then there’s the fact that the hybrid unit — while mostly reliable — is still a machine, and machines can have problems. Rinus Veekay’s hybrid didn’t work at all during his first qualifying run for the final row of the starting grid, while 2008 winner Scott Dixon had his practice Monday cut short after just six laps when a warning light blinked for an overheating issue. Nevertheless, the hybrid technology will play a part in “The Greatest Spectacle in Racing” on Sunday. And if it comes down to the final laps, it could be a big part, as the leader tries to hold on and the chasers try to time their boost for a winning pass.

“I think it definitely adds some variables,” said Dixon, who will start on the second row. “If you’re sitting out front, you could be a bit of a sitting duck, especially if everybody is kind of recharged and ready to go behind you.

“I think the biggest thing that we’ve probably all learnt so far, you’ve got to be ready for change, is probably the biggest thing,” he added. “But I think it could ultimately change how the end of the race plays out.”