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In an effort to break the Indy 500 record, IndyCar allows bigger turbos (Update) UPDATE
Honda IndyCar engine
With two years of strong competition between Chevy and Honda under IndyCar's 2.2-liter turbocharged engine formula, planned upgrades for the 2014 season have given both manufacturers some leeway to make more horsepower and torque.

The 2.2-liter displacement remains unchanged, but many items have either been opened for re-homologation or redefined.

Of the open areas for Chevy and engine partner Ilmor Engineering, and Honda through its Honda Performance Development arm, almost everything that attaches to the block was available for a complete redesign or major modifications.

"The whole top end, basically from the fire face up is what Chevrolet took a look at and improved on or went away and redesigned and hopefully came up with a gain," Ilmor IndyCar program director Wayne Bennett told RACER. "That's what we did. Basically from the fire face up, the heads are different based on the same casting, the plenum is different, induction system, fuel system. All of things we're allowed to change we did."

The move to a larger spec turbo allowed Chevy and Honda to start from scratch with new exhausts, turbo piping, a larger plenum, and to position the turbos within the chassis as they desired. New heads, provided they fit within the existing casting, and new camshafts are permitted. High-pressure direct-injection fueling has been the norm since they began racing in 2012, and both manufacturers took the opportunity to combine what they've learned with fresh ideas as new DI systems were developed during the off-season.

"The homologation table gave us many items to look at," added former HPD technical director Roger Griffiths, who spoke with RACER before leaving the firm. Cylinder heads, camshafts, induction system – it's all new because of the twin-turbocharger layout rather than the single for us. We looked hard in every area. I don't think there was any part that was not looked at, that didn't go untouched. Some areas gave a good opportunity for improvement. You have that list in front of you. Everybody in the past year or so you've been looking at what the 2014 engine could be to look at all of things that you would've done differently if you had the time again.

"You can't just take one item in isolation, everything works together. So if you come up with a new port shape for a new valve size, or whatever, there's an interaction with what's going on with the piston crown and what's going on with the camshaft, the lift or the duration or both, the timing. Everything works together. With direct injection the whole system is a lot more sensitive to what's going on. So you can gain power and you can lose power if you don't get that recipe right. So you've got to pay a lot of attention, you can't just assume that everything that you think is going to be better will be better because if you don't get that combination right, you'll be off the pace."

The rule limiting new heads to fit within the previous casting was done to reduce costs, according to Griffiths.

"It does limit the scope of what you can do but it was done with cost as one of the driving forces when we laid out the regulation," he explained. "Between IndyCar, Honda and Chevy, we looked at what's the sensible way to go. Was it all new cylinder heads where you could have completely free reign over everything? That would involve new castings – which means new tooling, which is pretty expensive. You're talking about hundreds of thousands of dollars for the tooling. What we tried to do was give ourselves the flexibility to work within what we had.

"When you designed the original casting, you left that amount of material in there for future improvement, you have to get the balance right between not creating a cylinder head that's monstrously large so you can change the port shape, you've got a water jacket in there so you have to respect that, that kind of thing. You give yourself a little bit of latitude but you also have to remember that you don't make something that's bigger than necessary. So it was trying to find the right balance between giving yourselves opportunity to play around with the combustion chamber and things like that versus trying to keep the development cost under control." More at Racer.com

03/10/14 IndyCar has made it clear that they want the Indy 500 qualifying record broken by the 100th running of the race.  That means more HP and the best way to get more HP is more turbo boost or bigger turbochargers, or both.

Ilmor Engineering Chevy IndyCar program director Wayne Bennett told RACER, the spec Borg Warner turbos offer increased performance where it's needed.

"Being slightly bigger, it is more efficient, and it's mostly at the top end," he said. "What that will do is help the turbo to not work quite as hard at higher RPM to make boost, and that will keep the air temperature down and increase performance that way. The only other change we saw was slightly worse [throttle] response."

Honda Performance Development technical director Roger Griffiths told RACER, "The general reason for it was a while ago, when the topic of twin-turbo versus single-turbo came up, we debated merits of each, and asked Borg Warner what they had that was a better match for our engines," he said. "What we were using were off-the-shelf items, and whilst they worked quite well, we'd hoped they had come up with something newer since we brought these engines out in 2012 that worked throughout the entire power band.

"They presented a variety of choices for us, and the best one was a bigger turbo that offered some improvement in the efficiency, but it's subtle and comes from aerodynamic changes to the turbine wheel. So we said that if we were going to be forced to go from our single to the twin, we said we wanted to do it with turbos that pulled hard all the way to the redline. It meant some sacrifice down low, but it's small. I was also looking at where we're going in the future, and if we're asked to make more boost, I wanted a solution that gave us some headroom."

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