Developed around an Oreca chassis (as was the current Acura DPi car), the 2023 Acura GTP/ LMDh car had its shakedown at Circuit Paul Ricard in mid July with HPD factory driver Ricky Taylor and HPD engineer Matt McMurry, an IMSA class champion, taking turns at the wheel. A month later HPD finally provided some information on its engine.
The Acura ARX-6, which will make its competition debut next January in the Daytona 24 Hours has a bespoke V6 twin turbo of 2.4 litre displacement. This is sandwiched between the Oreca chassis ‘spine’ and the spec transmission and hybrid system mandated by IMSA.
The new engine is dubbed the Acura AR24e and is the smallest displacement engine HPD has produced for Prototype racing, following its production-based 2.8 litre LM P2 and 3.5 litre DPi V6 twin turbos and before that its naturally aspirated 3.4 and 4.0 litre V8 pure race engines.
The AR24e has the same displacement and 90 degree bank angle as the twin turbo V6 currently under development by HPD for IndyCar racing from 2024, which likewise will be direct injected and married to a spec hybrid system.
The LMDh performance target is 500 kW / 670 bhp which is comparable to the output in Indy spec of the 2024 IndyCar engine, which is being developed to run on ‘sustainable fuel’. However the IndyCar engine is restricted by regulation to 12,000 rpm, the LMDh by regulation to 10,000 rpm. HPD says that the AR24e’s combustion chamber “has been designed to run on sustainable low-carbon fuel”.
If the LMDh engine requires higher boost in view of its lower maximum rpm to reach the mandated peak power level, overall its average plenum pressure requirement is unlikely to be far away from that of the 2024 Indy engine. It would be very surprising indeed to find this engine is fundamentally different from the (by regulation) 96.5 mm bore IndyCar engine (which has a stroke of 54.6 mm for 2396 cc).
Both the LMDh and IndyCar 2.4 litre V6 twin turbos have not only been designed and are being developed by HPD but are also manufactured in its Californian facility.