Using a 2.4 liter turbo V6 for its new ARX-06 GTP car is either a brilliant strategy, or a blunder of historic proportions that will act as an albatross on Acura’s neck for at least the next five seasons.
The new IMSA GTP era starts this weekend with the 24 Hours or Daytona, and at the top of the 61-car field will be the new hybrid GTP class. Acura and Honda Performance Development, which won the last DPi Manufacturer and Team title in 2022, will be fielding two cars against old rival Cadillac, as well as newcomers Porsche and BMW .
All the cars use a spec hybrid system that adds about 40 horsepower to the package. Acura’s rivals all elected to use V8 internal combustion engines of at least 4 liters displacement, either naturally aspirated (Cadillac) or turbocharged ( BMW and Porsche).
Honda Performance Development went a wildly different direction by developing a brand new 2.4 liter V6 with twin turbochargers. The engine was originally designed to be shared with Indycar beginning in 2024, but indycar has ditched the planned upsizing and will stick with the predecessor 2.2 liter engine for the foreseeable future.
The HPD 2.4 liter should be lighter and produce the same power as the V8 alternatives in the performance balanced class. But will it suffer under high-traffic situations?
*What were Acura’s alternatives?
*
The
GTP
formula specifies that the combined Internal Combustion Engine and Hybrid unit produce no more than about 670 horsepower. So there were plenty of options for
HPD
to consider:
Continue with the existing J-series 3.5 liter V6: This engine won three Dpi titles in the hands of Team Penske, Wayne Taylor Racing and Meyer Shank Racing. So it was a perfectly reasonable, proven option. And it would have cost very little to develop. But for racing, the 60-degree V was sub optimal with a lot of weight high in the chassis. Also, it was limited to about 6300 RPM and ran out of breath on longer straights.
A different production-based engine: HPD could have built a racing engine based on the 3.5 liter NSX engine (which already powers the NSX GT3), or the 3.0 liter DOHC V6 type S engine hardened for racing. Developing either of these likely would have cost nearly the same as the new racing engine, and would not have all of the advantages of the racing power plant, especially the lower center of gravity.
A clean-sheet racing engine: At the time the IMSA powertrain was being developed, HPD was in the midst of developing a 2.4 liter V6 for Indycar to replace the 2.2 liter used since 2012. It was designed to work with Indycar’s planned spec hybrid system, so using it in IMSA for the same purpose made some economic sense. And the 90-degree V lowers the center of gravity a lot compared to other alternatives.
*Advantages of using a V8
*
Why didn’t any of the other three competitors in
GTP
go with a relatively small purpose-built racing V6? In addition to the cost of a brand new purpose-built racing engine (which none of them used), it likely came down to the characteristics of multi-class racing. Top class cars are often called upon to get around slower cars quickly. What is required in that situation? Torque for quick acceleration. The common logic would recommend a high-torque, relatively high displacement V8. Like the Corvette-based engine in the Cadillac and the turbocharged V8s in the
BMW
and the Porsche. In those traffic situations, a small-displacement V6 would appear to be at a significant disadvantage.
*Advantages of a small V6
*
HPD
says that it came to the conclusion at the beginning of 2022 that the future Indycar was the way to go with the
IMSA
powertrain. This came after weeks of intensive simulation runs. That plan runs counter to common assumptions about how best to deal with traffic. What does
HPD
know that others don’t?
HPD
isn’t saying at this point. But we can make an educated guess or two.
As we mentioned before, the GTP class will be performance balanced. IMSA will make adjustments to assure competitiveness. But some characteristics are easier to balance than others. Horsepower is limited in GTP and torque output can be balanced. All the cars should be close in downforce and drag due to IMSA wind tunnel testing and aero homologation. So power and terminal speed of all the cars should be similar, and would have been no matter what power plant Acura chose.
The way that the manufacturers use the hybrid system is open to development. Perhaps HPD , working with F1 engineers at HRC , is using the hybrid power to fill in the torque holes of the smaller v6 in some innovative way.
Another possibility is HPD and Oreca (the maker of the Acura chassis) are going all out to maximize vehicle dynamics. It would be very hard to Performance Balance vehicle dynamics. The racing V6 should be lighter than its competitors, with a lower center of gravity. This would allow HPD and Oreca more ballast and options to distribute ballast than competitors. This would give the teams more race-to-race options for modifying the chassis to fit the characteristics of particular tracks.
All of the GTP cars are longer and have more of a rearward weight bias than the Dpi cars they replace. The Acura should have less of this rearward bias because of the lighter engine, and the engine mass will be lower in the chassis that its competitors.
There are changes to the IMSA sporting regulations for 2023 that might have played into the decision. In particular, teams will have access to fewer sets of tires over the course of a race weekend, and the tires for 2023 are harder than last season to compensate for the increased vehicle weight. That factor, along with the increased weight and reduced downforce of the new cars, could have led HPD to go all-out for vehicle dynamics.
The 2.4 liter engine can rev to the 10,000 RPM limit. No other power plant can. This could yield a very wide power band.
Where does this leave us? At the fork in the road between brilliance and blunder.
If we see the Acuras regularly qualify up front but get eaten alive by its torque monster competitors in traffic, then this will be a gamble that has failed.
But if we see that the Acuras are easier on their tires, and more nimble than their competitors with their higher displacement engines and bigger rearward weight bias, then we will see Acura dominance until its competitors figure out how to overcome the Acura’s superior vehicle dynamics.
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