The only word that comes to mind is baffling. In all aspects, at one of the premier racing events worldwide each year we find ourselves for the second year in a row staring at results that have yet to go official, and the balance of performance taking center stage yet again.
Going into the season with the newly defined BoP process was always going to be a work in progress, but it was so far off for a few teams in GTP, and in GTD, it found BMW and Ferrari “exceeding performance.” Without further explanation as to what the exceedance was, it cost Ferrari and BMW significantly in season-long points, but not the win. But where exactly did they exceed the performance?
I decided to dive into the data available to see if a trend can be found.
Before that, let us discuss the BoP IMSA monitors through its classes. Looking at the BoP tables gives us an idea of what we know they are looking at and caring about to determine performance. Boost pressure for turbo cars, fuel loads, aero and weight are the biggest ones we see as fans. But we also know from previous discussions that Michelin is reporting tire pressures, loading, and sets used. Refueling times and flow are monitored, which have caught out competitors in previous years. MSR most notably last year was altering tire pressures to gain performance, and that of Land Motorsport with a “faster than expected” fueling time in 2018.
It’s not exactly clear what either manufacturer violated. SC365 reported that BMW was seeking clarification on exactly what they violated. Ferrari and IMSA have not commented to date and it will be left up to us to figure this out.
One of the things I love about my job as a paramedic is that I get to assess a patient’s vague complaints and then use my knowledge to come up with a working diagnosis to make treatment decisions. We can do the same thing here with the “exceedance of performance.” In the world of EMS, we begin our diagnosis with the initial complaint and dispatch information to help form a picture for treatment, I did the same with the issue here at hand and formed my working hypothesis initially around the weather between the BoP testing in December and the race.
As the Ferrari 296, and the BMW M4 GT3 are both Turbocharged cars, my first thought was the air density during the Daytona 24 was higher, causing higher-than-expected performance.
To gather this data we have to know a few things. The first is the weather, thankfully IMSA provides this data for all sessions. Secondly, we have to know the specifications of each turbocharger. Finding this information was tricky, and I’ve had to make some assumptions here.
The stock BMW M4 uses a TF035HL-4W Turbocharger from Mitsubishi and has been used widely throughout their automotive lines. The horsepower reported from BMW’s literature on the car would suggest that they are not using anything more than a stock turbo housing with a modified cold side impeller, exhaust manifold, piping, and boost control equipment. Reliability is key in GT3 and there is no reason to shy away from a well-proven unit capable of producing upwards of 750hp with modifications.
Ferrari is using a modified RHF55B from IHI that is present on the 488 GT3 and the F8 Tributo, this is reportedly an evolution of those two designed for better spool times and efficiency.
Both of the spec sheets on these are similar enough that we can make some general assumptions on performance with the given atmospheric conditions. We will get to this a bit later.
There is an interesting thing about wondering about the boost limits - what about the Aston, Acura, and McLaren?
The BoP process is a mystery, kinda.
We have to look at both the sporting regulations and the BoP tables to be able to understand how IMSA is putting these together.
For the Roar where the Daytona and the remainder of the 2024 BoP would hit it’s starting point, we are going to look first at the boost tables that were set.
It became evident that the M4 and the 296 are running a much higher boost ratio across the rev range than their competitors. The ratio is defined in the Sporting Regulations and it requires math with numbers that are not available for review that would give us a better indication of boost pressure through the rev range. But we do know what the boost limits are based on the BoP tables.
For the Roar before the 24, this is the GTD BoP that the teams were given, the updated BoP for the race came out and had the adjustments listed based on the performance recorded at the Roar.
We can see that the BMW and Ferrari had changes with the 296 seeing a standard change and the M4 having the most adjustment in the middle of the rev range.
What this equates to in actual pressure loss isn’t easily known. But the key part of this here is what they took away, and another part of the performance plan where I think we saw the “exceeding of performance” occur.
Acura, Aston Martin, and McLaren all have a lower boost ratio because of how they make their power through the engine’s volumetric efficiency.
But what about the rest of the BoP?
As I said earlier, part of my job as a paramedic is to look at the information I’m given and decide what is relevant to the patient I’m looking at. For example, if I’m presented with a patient with chest pain, I’m going to do an EKG to see if the patient is having a heart attack, but it comes down to the story I’m told to help me solidify my case and course of action. In an instance like this I want to hear keywords, or triggering events - things like “I’m sweaty and nauseated and I just finished mowing the lawn” is a much different story when it’s a 19-year-old college kid or a 65-year-old pensioner who has previous heart history. Of course, it’s entirely plausible that 19-year-olds might have a cardiac structural defect, but it’s more likely that the 9 energy drinks they’ve consumed, coupled with poor sleep have found us in this situation. It’s much more obvious for the 65-year-old as to why they’ve called for an ambulance.
So let’s dissect the facts.
When we look over the lap times and deltas, stint lengths, pit times, and all other obvious items that BoP would affect, there is not a consistent trend. Both of these models were in line with the rest of the GTD and GTD Pro fields and I don’t think the “performance exceedance” occurred in these locations. Also, it’s very important to note that had the cars failed in any of these other categories, they’d have found that in post-race tech, or IMSA would have adjudicated penalties in the race as they’ve done previously.
Both the #1 and the # 62 from Paul Miller and Risi Competizione respectively were sent to Parc Ferme for post-race investigation as is normal. They passed that section without problem so the rest of the BoP issues can be tossed aside and ignored.
What is the issue then?
When I was going over this data, the point that struck me the most was a parameter IMSA calls “High Overboost Limit” as well as the “Low Overboost Limit.” Essentially these two parameters are limits that cannot be exceeded. In the sporting regulations the “Low Overboost” is allowed to be met or exceeded 5 times, this is reset when the car crosses the pit in/pit out timing loop. The “High Overboost” limit is a single instance that can never be met or exceeded. The Technical Regulations define the low condition as 30mb(0.4psi) over 1-second duration and the high as 100mb(1.4psi) over 1 second.
Turbo systems use a wastegate or diverter valve to control boost. To avoid boost spikes and boost creep, the wastegate has to be able to respond in time to control the flow. Both of the turbocharger types I think the M4 and the 296 are using have internal wastegates. These are normally fine for many applications and don’t have many problems unless the wastegate is unable to handle the flow or doesn’t respond fast enough to dump the excess boost. When that occurs we get boost spikes, or boost creep - which, if not worked around or dealt with, would result in a low or high over-boost exceedance.
During the Roar, the weather conditions were much cooler and much drier compared to that of the 24. When the BoP was set, it was based on the session conditions, given that it was significantly cooler and drier, the turbos would have been working less hard to achieve the baseline boost levels. Essentially, they’d have been far less prone to creep and spikes. In the hotter weather a few weeks later, to get similar performance, they had to work much harder higher into the rev range which would have led to spikes and creep.
That is exactly where, in my opinion, BMW and Ferrari ended up exceeding performance values set by IMSA.
Naturally, teams are going to maximize performance at every place they possibly can, I have no question that the plan was to run right up to the limit with minimal margin for the over-boost exceedance. I would do the same thing as an engineer. I think where they got tripped up was the weather being hotter, and more humid than expected.
The data sent to the scrutineering logger is coming from the same sensors the teams have for telemetry on the pit stand. It’s a Bosch CANBUS system. The other consideration I had regarding this came from the comments that BMW mentioned. Andreas Roos, in his interview with Sportscar 365 mentioned that they couldn’t find the discrepancy.
“This is what they say, but we can’t see it on our side,” he said. “So this is what we have to investigate and understand. - Andreas Roos
During the Roar, IMSA issued a CANBUS update for the scrutineering logger, it was a code change that involved the boost pressure sensors that lie in the intake manifold, along with several other changes. Is it possible that a line of code was bugged for the BMW and Ferrari during installation and it caused a discontinuity between the scrutineering logger recordings and the reported telemetry back to the pitbox? Yeah, I think it could be. I’m not familiar enough with the system to know if this is the case though.
The Fallout.
With the post-race penalties handed down, and for the second year in a row, we see teams get to keep their watches the podiums, and the trophies, despite running a car outside of the regulations. What happened last year with MSR was something that should have been punished harshly, the car deserved to be disqualified entirely, and the rest of the celebrations should have gone to the WTR Acura.
IMSA has now set a precedent that you can successfully run a car outside of the regulations, win, and take home one of the most coveted prizes in motorsport, and other than losing points and a mediocre fine for a factory effort, nothing bad will happen.
This is now a slippery slope, and when teams will do anything to gain an advantage, and IMSA refuses to penalize it appropriately, there is nothing that will stop anyone from doing this other than the loss of points. Unfortunately, it’s not enough - you can recover from this through the season if you run well enough and still take home a manufacturers and drivers championship.
If a Rolex is on the line, why wouldn’t you push the boundaries?
You have to do better IMSA. This is silly.
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