Chip Ganassi Racing (CGR)’s IMSA SportsCar Championship programme expanded from one car to two for the 2022 season, in the process re-branding itself as Cadillac Racing. With that, Danielle Shepherd was promoted from a CGR IndyCar simulation engineer to the lead race engineering role for the CGR-run #02 Cadillac DPi-V.R.

Shepherd’s debut as lead engineer was the 2022 Daytona 24 Hour race, in which her Cadillac Racing #02 DPi-V.R. proved fast enough to lead but not dependable enough to win. However, second time out, and staying in Florida, Shepherd engineered her car to victory in the Sebring 12 Hour classic.

Danielle Shepherd race-engineers the Cadillac Racing #02 DPi

At the following race on the 2022 schedule, at Long Beach in California, Anne Proffit caught up with Shepherd to quiz her on the challenge of race engineering a contemporary IMSA DPi car, with an emphasis on the operation of the powertrain.

The heart of the Cadillac DPi-V.R. is a production-based naturally aspirated 5.5 litre pushrod V8 (see sidebar: The Cadillac DPi-V.R.). ECR Engines fettles this and has Lucas Lafond in charge of trackside support for the #01 car, with Ian Magor in charge of trackside support for the #02. They both report to Scott Meesters, the program manager, sportscar engines, at ECR Engines. Judd Glenn is the chief calibration engineer.

Shepherd says she has a very good relationship with Magor and his ECR Engines colleagues. “They’re very responsive to questions. If I ask Ian how do we get ‘this’ out of the engine he is always right there with answers about it.

“Ian will be on the timing stand with us to watch his telemetry data live. Basically, he makes suggestions on different [engine] settings; we’re involved in that, though. Basically we watch the vitals, but his single role is to monitor the engine. So while we’re looking at some of the general metrics, we rely heavily on Ian to make sure everything is running on his side.

“We had fuel pressure issues in Daytona. Ian was communicating what the thresholds for this pressure are, and we were sitting there watching it too and asking how critical the issue is. Are we going to be fine? Should we go to the back-up? Do we need to come in? So it’s more of an open dialogue.

“We have an intercom so it’s easy to just ask him questions or have him look at data. He will also come into the debriefs and he’ll give suggestions on the drivers’ comments.”

Are the engine settings adjusted by the driver? “They can adjust the traction control setting, and they have some different throttle pedal sensitivities they can choose, but that’s pretty much all they address on their end. Then, if something goes wrong, if they are having certain engine issues, it would be under direction from Ian to make the necessary changes.”

And how is Ian with following your instructions? “Well, other than to make us go fast, I don’t know what instructions I have. He’s pretty good at making us go fast!”

How would you assess the significance of engine performance in DPi versus IndyCar? “I think it’s important in both series. Sometimes I’m not sure the engine techs realise how important every little bit of the engine [performance] actually is, especially for an IndyCar on an oval. There, every little bit of engine power they can give us can be more [to find speed] than we as engineers can do from the set-up. So any way we can get it, we take it.”

With all DPi cars running under a Balance of Performance (BoP), what do you consider to be the key engine characteristics? Is it top-end power, power delivery, engine response, overall engine driveability, fuel consumption?

“It’s kind of a combination. I mean, you need the top speed from it, in a sense, but you also need the fuel mileage. Top speed doesn’t matter if you’re burning too much fuel. So I feel like you need a balance of all those factors. Even the driveability in the lower gears, you need the driveability of the engine to make sure you aren’t compromising too much time in in those [slower] sections. So I think it’s a balance of top speed, driveability and fuel mileage.”

And having the right engine response and power delivery? “Yes – I put that under driveability, in the sense that it is the power delivery method. The driver’s pedal position to the actual torque response is the driveability of the engine, in my opinion.”

What are the Cadillac engine’s strengths and weaknesses in these respects? “Our engine techs are good, and they work with us so that we can try to save as much fuel as possible, and try to get ourselves in a decent position that way. And obviously they seem to have good driveability as well.

“Sometimes I think we tend to lack top speed but that’s not necessarily in the engine side of it; sometimes more the BoP side of it. And then the Cadillac chassis is good on some courses and the Acura is better on some of the others – the more aero-dependent ones. So there’s some trade-offs both BoP wise and just what each manufacturer is focused on or how they have done their development.”

To what extent is fuel consumption a major factor at Daytona and Sebring? “I think it’s a factor at every race track, even the long-distance races. If it goes yellow on track and therefore you’re coming in for a pitstop, you always want to make sure you have fuel in the tank to match your competitors.

Dancing in the dark: the #02 at Sebring

“You want to have as much fuel as possible, so that your stop is as short as it can be, so you don’t lose time to your competitors. Or you can beat them out of pit lane and back onto the track. So you’re always trying to make sure you have enough fuel not to compromise track position, but also you don’t want to compromise lap time. You kind of want to find the optimum balance between lap time and fuel consumption.”

Can Ian Magor do anything to influence fuel consumption during a race? “In general, no.”

So what factors do influence it? “A lot of it is driving style, just how they are on track, how they are using their right foot. How aggressively they’re on throttle. They can lift and coast into corners; if they’re doing that efficiently or not. And how they are in traffic. How well they’re going through traffic is a lot of it as well.”

Do your two primary drivers, Earl Bamber and Alex Lynn, complement one another in terms of driving style? “Luckily, yes. I feel like it’d be really difficult if they didn’t.”

What do you have to do during the race to influence fuel consumption? “Obviously before a race, we talk about strategy. And we typically have a fuel target number for a stint. The driver has to go however many laps we feel necessary for his stint.

“And then they have [real-time] information about what their fuel consumption is and what they would need to go one more lap. Sometimes that’s feasible, sometimes not. The idea is that we can manage with them how much fuel they’re using to try to hit our targets.

“Also, it doesn’t help if you need one more gallon to do one more lap but you have only 0.9 of a gallon, then you will be coming in with more fuel than you needed to. Maybe you lost lap time for not actually gaining an extra lap. So it’s good to make sure the drivers know where they are in the fuel-saving process.”

Traction control is another key driver input? “Yes, different settings are programmed into the ECU, and then the drivers have knobs on their steering wheel that they can use to increase the amount of traction control or decrease it. Basically, they start in a middle range of traction control and then the driver can turn it up or turn it down as needed.”

Is the traction control setting the same from corner to corner? “At Sebring they would like it to be adjusted corner by corner but it is a manual adjustment. So there are places where they want it to be corner by corner, but it depends on whether they can actually adjust it and by how much.

“A lot of it depends on the track conditions at the time. So a lot of it will be a gradual change based on the conditions and how the track is evolving.”

Is the clutch and its set-up the same from circuit to circuit? “Yes.” To what extent do you change gear ratios from circuit to circuit and from testing to practice to the race?

“In general we do but that’s one difference between the DPi and the IndyCar – the Cadillac gear ratios are quite a bit coarser than the IndyCar ones, which are quite a bit finer. So while you have a lot of adjustability on the IndyCar side with the gears – and that was a lot of my focus on the simulation side – there just aren’t as many options for the DPi.

“And just the way engine responds to the gearing; it’s just not quite as defined as on the IndyCar side.

“Wind direction obviously plays a factor. If the weather’s the same across the whole weekend then there’s no reason to change gearing. If for some reason there is going to be quite a big shift in wind direction, you might need to change ratios. But often with the DPi if you adjust for one place on the circuit you’re compromising in another, so it’s kind of deciding where those compromises should be.”

Do you run the same differential settings everywhere? “We have played around with the differential a bit in testing but at this time our settings are pretty consistent.”

Is race engineering a DPi harder than you imagined?  “I maybe never thought about how hard it was going to be when I started. I mean, lead engineering the #02 DPi comes with the same challenges as engineering any car would. There’s a lot of managing some of the finer details that I’m not sure I knew was part of the position, although I’ve been around long enough that I kind of knew what the position entailed.”

What are the secrets of winning a 12-hour race? “Have a fast car and a little bit of luck.”

How does it feel to be the first lady since Leena Gade to engineer a winning Prototype at Sebring?

“It's exciting. I mean, I’m here to be a race engineer to win races. And yeah, whatever I can do to inspire others to join me in racing is great.”

Leena Gade has won both Sebring and Le Mans. How realistic do you feel it is to match that feat one day? “That’s why I’m here. That’s the goal!”

DANIELLE SHEPHERD

Born on July 20, 1992, Danielle Shepherd hails from Northfield, Ohio. Encouraged by her mother and a grandfather, she grew up following racing as a fan. At college she double-majored in maths and physics, and her maths adviser helped her obtain an internship with a maths professor at Davidson College, North Carolina, who was working with racing teams.

That internship led to Shepherd joining KV Racing Technology in 2015 as a data acquisition engineer. After the team closed she moved to a similar role at CGR, on Charlie Kimball's car, in 2017. For 2018, she graduated to a simulation engineering role, initially for Scott Dixon’s car. As such, Shepherd was part of the CGR Dallara-Honda engineering team behind Dixon’s 2018 IndyCar title, and she played a similar role in Alex Palou’s 2021 title.

Shepherd’s last IndyCar race was 2021’s September finale at Long Beach, where it shared the bill with a round of IMSA’s DPi SportsCar Championship. Having seen the CGR-run #01 Cadillac in action there, she went to the IMSA finale, the 10-hour Petit Le Mans at Road Atlanta, in November as an observer, albeit not yet knowing she would be lead engineer for the #02 car to be added the following year. 

“The longest race I had been involved in was the Indy 500,” she says. “So, at Petit Le Mans I was learning about things like how they transition the drivers. How they do the balancing of the multiple practice sessions and of the multiple drivers. Even just learning some of the IMSA rules I wasn’t as familiar with: how they do the caution flag periods, for example.”

Shepherd and the crew assembled to run the #02 car were able to do a test at Road Atlanta and then another at Daytona, before the Daytona season-opener. These days, that event incorporates the ‘roar’ practice and a qualifying race, which are held one week ahead of the 24 Hours.

Thus was Shepherd thrown in at the deep end. “Luckily, John Hennek had been engineering the #01 car last year and he could give me the benefit of his experience. It helped to have someone to lean on when some of it was new to me.”

Asked how engineering a Prototype differs from engineering an IndyCar, Shepherd notes that both have extensive and sophisticated data acquisition. “However, there are some different tools on an IndyCar, some things you can adjust that you don’t have on a Prototype – IndyCars have adjustable front wings, for example.

“Obviously they’re different car configurations and there’s a lot more that’s homologated on the DPi. There are things that aren’t quite as well-defined on the IndyCar side. But in general, a racecar is a racecar. Still, there are the fine details that you use to adjust the car that vary between the series.

“And then obviously, on the strategy side, they’re different. The strategy is different doing a long race versus doing the shorter, lap-defined races they have in IndyCar. And even just the way the yellow flag periods work differently can change the way you work strategy-wise during the race.”

Despite Shepherd’s inexperience, her car was fast enough at Daytona race to lead the 24 hours, only for various issues to cost a good result. “It was a bit on our side, in trying to get a brand new car up and going, some details got overlooked. But then from that you update your procedures. And that’s what makes you better in the long term.”

Good enough in fact that the very next race at Sebring brought victory.

THE CADILLAC DPi-V.R.

The Cadillac DPi-V.R. was introduced in 2017. It is based on a Dallara LM P2 chassis and has homologated GM-designed bodywork. These days it runs on spec Michelin tyres.

The engine is a GM production-based naturally aspirated 5.5 litre pushrod V8 fielded by ECR Engines. Initially, in 2017, this ran at 6.2 litres, as profiled in RET 103 (June/July 2017). The modifications involved in the switch to 5.5 litres were detailed in our 2018 24-Hour Prototype Engine report (RET 112, August 2018).

In the Grid section of RET 116 (February 2019) we described the development of the 5.5 litre version through to the start of the 2019 season. Since then its specification – having been homologated – has remained essentially unchanged. Under IMSA's Balance of Performance (BoP) the car ran a pair of 31.9 mm intake air restrictors in 2019, and since 2020 has had a pair of 32.2 mm.

Maximum rpm is set by IMSA at 7600 rpm while, with the fuel a mandatory VP E20, the compression ratio is homologated as 12.5:1. The 2019-20 restrictor size increase was an increase in intake area of only 1.8%, and top-end power rose from 562 to 570 bhp. Maximum power is made at 6800 rpm with torque topping out at 460 lb-ft (624 Nm) at 5900 rpm.

The DPi-V.R. V8 has Mahle pistons driving a Bryant crankshaft through Carrillo con rods.

Routine mileage is within the 3800-4000 mile range, and the engine has proven highly dependable over a number of years. It helps that ECR has been working with this naturally aspirated platform for many years. Compared to its turbo-supercharged 3.5 litre V6 Acura rival, individual cylinder pressures are lower, while any time cylinders are cut for traction control, there is greater resolution than in the case of fewer cylinders.

Pit stop for the #02 en route to victory in the Sebring 12 Hours

ECR handles all the vehicle traction control and shifting. The engine is run by a Bosch EMS with ECR Engines’ firmware. The clutch is a manually controlled 5.5 in Tilton triple plate carbon-carbon item, while the six-speed transverse gearbox has a sequential shift operated via steering wheel paddles.

The gearbox is the Xtrac P1159F, which has its origins in the transmission used by the 1999 Le Mans-winning BMW. The P1159 model was introduced in 2014 for LM P1, with a six-speed version for LM P2 following in 2016. The DPi 1159F has been used since the current cars were introduced in 2017.

Input is via a pair of bevel gears with the straight-cut ratio gears arranged in a ‘cassette’ cluster for ease of ratio changes. The straight-cut final drive feeds via an Xtrac limited-slip ramp and plate-type differential with output flanges to suit tripode joints.