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[h=2]Insight: Next step for IMSA DPi[/h] By Marshall Pruett / Images by LAT

The reaction to IMSA's new Daytona Prototype international formula has been overwhelmingly positive since Cadillac, Mazda and Nissan brought the concept to life late last year.
Cadillac's stretched DPi-V.R, with its throaty 6.2-liter V8 and sharp bodywork fitted to Dallara's base 2017 LMP2 chassis, has conquered everything in its path during the opening rounds at Daytona and Sebring. Mazda's curvy, flowing RT24-P (below), built on the Riley/Multimatic Mk 30 chassis and propelled by a stout 2.0-liter four-cylinder turbo, has shown pace and potential. And the angular Nissan Onroak DPi, constructed upon Ligier's JS P217 chassis and powered by a 3.8-liter twin-turbo V6, has demonstrated serious speed amid technical teething pains.
In a short period of time, the custom, IMSA-only DPis have revealed specific strengths and weaknesses, and with the three models at various stages in achieving their full potential, the next step in the introduction process is to understand the development options available to the DPi brands.
Simply put, now that IMSA's custom DPis are here and racing, what can teams and manufacturers do to make alterations and improvements with their aero or to the technology beneath the bodywork?
"Once they are homologated, unless they have a demonstrated need for some safety items, they are going to be locked down in their homologation through the life of the car," Geoff Carter, IMSA's Senior Director of Technical Regulations and Compliance, told RACER.
At present, all three DPi models are competing under draft homologations. During this draft period which has no specific end date in place, according to Carter, Cadillac, Mazda and Nissan can lobby IMSA for changes to be made to their cars. IMSA can also use this time to contemplate the final homologation specifications for each car and call for any changes it deems necessary.
One example of the DPi draft homologation process took place during pre-season testing when the Action Express Racing Cadillacs arrived at Daytona fitted with brakes supplied by AP and the Wayne Taylor Racing Cadillac (below) came with Brembo's equipment installed. With two options to consider for the DPi-V.R during the draft phase, Brembo was ultimately chosen as the sole vendor for the car and AXR made the switch beginning at the Roar Before the 24.

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A deeper look into the DPi rules reveals an interesting decision by IMSA. Despite taking the base rules established by the ACO and FIA for 2017 LMP2s in a completely different direction with manufacturer participation and custom bodywork and engines, IMSA still elected to pattern its DPi governance after the European spec LMP2 system. The choice to use a French template for North American DPis – especially after the ACO/FIA banned DPi participation at Le Mans and in the World Endurance Championship – is another interesting call by the Florida-based sanctioning body.

"The short answer is [the DPis] are in general bound by the same rules," Carter added. "IMSA is respecting the same homologation standards and rules of the FIA/ACO."
It means that once IMSA moves the three DPis from draft to final homologation, the Cadillacs, Mazdas and Nissans will, in effect, be locked into the same type of rigid technical configuration as their spec 2017 LMP2 counterparts. As Carter explained, with the homologation process closed, no innovations or mechanical/aerodynamic component changes will be permitted.


Giving DPi manufacturers one shot up front to get it right with big decisions on powertrain choices, aerodynamics, suspension design, and vendors to create the car is a tall order. Although the draft homologation period provides some flexibility to make fixes, once it closes, the inability to make further changes – or to use the DPi platform to develop new technology as it emerges during the car's lifespan – is another unique decision taken by IMSA.
With chassis, engine and aero developments banned at the conclusion of homologation, the only recourse for changes of any kind would come from the use of an aero "joker," which is also based off the European rules.
"[DPi manufacturers cannot make aero updates] unless they want to do an EVO, but the procedure for that is pretty well laid out in the P2 regulations," Carter (pictured) said. "The FIA and the ACO, they do have what they call a 'joker.' So if a P2 car feels like they need to use the joker, there's a whole process they can go through to resubmit an aero program using the joker."
Provided a DPi manufacturer approaches IMSA about using a joker, the series has a formal process in place and timeline for its receipt.
"It's a pretty delineated process," Carter continued. "The long and short of it is for a current homologated car, if they want to apply for any sort of a bodywork change in terms of styling, that there's a whole process of CAD submissions, CFD and scale model testing that needs to be applied for by August of the current year, whichever year that is."
Based on the DPi aero performance data IMSA has captured so far through CFD and wind tunnel testing, Carter does not anticipate the need for Cadillac, Mazda or Nissan to ask for bodywork changes.
"We went through and did all of the aero testing to put these cars from scale to full-scale in a performance that we are comfortable with," he said. "So from an aero standpoint, we are very comfortable with the aero on these cars now. We don't feel like there are any of them that are outside the box.
"And, the tools that are listed on the aero table are the tools necessary to make sure there is parity from an aero standpoint to the [spec 2017] P2 cars as a reference."
Altogether, IMSA's chosen approach to managing the DPi formula in competition places full responsibility on its technical department to use Balance of Performance to regulate the competitiveness of Cadillacs, Mazdas, Nissans and all incoming DPi models through BoP.
Whether IMSA will reconsider its spec treatment for DPis in the future, or whether – as Carter noted – the series intends to keep DPis "locked down in their homologation through the life of the car" will be yet another interesting thread to follow in the years ahead.