As the NTT IndyCar Series and its engine suppliers prepare to launch the 2021 season this weekend, the work will continue behind the scenes by Chevy and Honda as they develop their new-for-2023 hybrid motor package.

That’s the norm when a racing series sets an ambitious change in motion for the future. Despite having a new season to run, Chevy’s partners at Ilmor Engineering and the Honda Performance Development group remain entrenched in a second, private race away from the spotlight to get their 2.4-liter twin-turbo V6s on the dyno and making big, reliable power.

Speaking with Darren Sansum, IndyCar’s director of engine development, there are a few areas Chevy, Honda, and any new engine suppliers can play with on the design side as the series looks to retire its 2.2-liter twin-turbo V6s at the end of 2022 and welcome the 2.4s mated to kinetic energy recovery systems.

“From a high level, the 2.4-liter is actually not so different to the 2.2,” Sansum told RACER. “There were some things that were open on the 2.2 to homologate at the beginning in 2012, but we’ve actually converged on one solution. So for example, bore size used to be a freedom, as long as the swept capacity met the criteria. We’ve actually fixed the bore size for the 2.4 at the request of the manufacturers so that they don’t have to go and do a lot of rig work in order to determine the optimum bore size.

“We just said, ‘Well, let’s just agree on one and then it’s the same for everybody.’ But there are freedoms on bank angle with the V, therefore crankshaft design and those such things are open. The 2.4 fits in the same package as the 2.2; it’s the same length and it will fit in the current car. Crank center height’s the same. What all that means is, with a larger capacity engine in the same dimensions of the 2.2, it’s quite a challenge on the crankshaft design. You’re trying to pack more bang inside the same physical package.

“And these engines are already pretty highly loaded. The bottom end is under pretty significant stress, being a turbocharged engine with very high specific output. So the new engines are going to be a good challenge for the manufacturers on getting that design right.”

The 2.4L motors must, by rule, fit within the dimensions of the current 2.2L motors and bolt directly into the DW12. (Marshall Pruett/RACER)

In the decade or so since the 2.2-liter V6 formula was unveiled, new manufacturing technologies have reached the mainstream. One popular tool could be used with the 2023 motors, as 3D printing is on the list of approved methods for engine suppliers to employ. The long-held and expensive process of casting major engine components could fall prey to cutting-edge additive production.

“The engine block, for example, must remain aluminum, but it doesn’t necessarily have to be a casting anymore,” Sansum said. “We’re allowing some different manufacturing techniques for the cylinder block, which will allow some freedoms. As the regulations are written right now, there’s nothing new and nothing specific about additive manufacturing, but we are actively discussing with the manufacturers on how to address that in the future.

“We are looking at those because obviously there’s a huge explosion in the area. There are components from the engine now that are additive, that’s no secret. You only need to look at the exhaust systems to see that. There are external pieces that you can see. But there are bigger areas where you could spend a lot of money on making additive parts and potentially you get quite good advantage, but we’re trying to keep that cost capped.”

Sansum, Chevy, and Honda are working on a new minimum weight figure for the 2.4 as well. Although the motors will not be any larger than the 2.2s, a planned hike in horsepower to the 800-900 throughout the 2.4’s lifespan will likely see more metal used in key areas to add strength and robustness.

“The 2.2 is 112.5 kilos (247.5 lbs), and the 2.4 is heavier than that by a little bit,” he said. “We’re close to an agreement on the new number. And we are sticking to the same number of engines in a lease per season, so they’ll not be allowed any extra engines, and the extra weight allowance does give them the freedom to make some parts stronger. It’s completely up to them on how they use that extra weight.

“Obviously again, go back to the crankshaft does get heavier because it’s going to have to be bigger. So that’s one of the main things that will get heavier.”

Both manufacturers are already well down the road with the development of their 2023-spec engines. Lumen Digital Agency

New turbos are part of the 2.4-liter package as the series and engine suppliers look to added boost to assist in the power increase.

“It is a new turbo design for the new engine,” Sansum said. “Because of the increased air flow of the engine, we’ve got to reoptimize the turbo maps, so we’ll reoptimize the compressor and turbine size in order to be operated in a better position. So that all agreed to and prototypes are available.

We’ve also gone up nominally on boost so we’ll have a power hike equivalent to the capacity increase. So our base boost level at road courses will be up from 1500 millibar (21.75 psi) to 1600 millibar (23.2 psi), which is just the smidge under where we at for the push-to-pass right now.”

The biggest piece of the 2023 hybrid 2.4-liter puzzle left to solve is the introduction of harvesting and deploying electric power to complement the twin-turbo V6’s output. While IndyCar has settled on a KERS solution for road and street circuits, and for ovals as well, Sansum isn’t ready to reveal their plans, but he was willing to share some general insights.

“It is interesting, and you will be excited by it,” he said. “The idea of using the system for push-to-pass is still our primary goal, and not having it automatically engaging and supplementing the internal combustion engine as it does in Formula 1, but to essentially replace what we do with the push-to-pass boost right now. So we’re looking to remove turbo boost push-to-pass and replace it with this.

“We’re not sure yet where we’re going to need to artificially limit the amount of use or just allow it to organically play out. So that’s on the power side. And then on the regeneration side, we’re looking at a number of different modes on how to regenerate that. It’s a particularly interesting topic. At the ovals, no one has done this yet. We think we’ll be the first. And so obviously our biggest show is here at Indy, and that’s the one where focus is on how much energy can you generate at the Speedway?”

Standard practice for race engine manufacturers is to build a test a single-cylinder model containing its ideas for how to get the most out of a new formula, and once those concepts are proven or discarded, it’s time to move onto building a full-size prototype. Both Chevy and Honda would be expected to have been running single-cylinder test mules for a while now, and with the shift to 2.4-liter V6s as the next step in the process, Sansum will ensure development stays within the boundaries of the regulations.

“We do stand back to some extent as the manufacturers are extremely private about what they’re doing,” he said. “They’ll give a little snippets away, but like, ‘Oh, we have a prototype or we found something valuable kind of information,’ and it is at the point now where it’s no secret that they both, are in the process of testing things. So very soon as we start going through the rest of this year, I will be inserting myself in and seeing what they have in order to make sure that we don’t get any big surprises when it comes around to homologation at the end of 2022.

“We don’t want to find their interpretation of the regulations is different to my interpretation. So it’s definitely time to be involved in that loop now, and we will see the engines intimately from the inside out to make sure that they don’t get any surprises. You can’t get so close to the racing season and then find out the wrong path had been followed.”