Why does the BMW M4 GT3 Evo have to compete with a new turbocharger this year via a re-homologation? BMW Motorsport Director Andreas Roos argued that the change in the car's fifth year of competition - the second with the Evo package - was due to costs. "The main reason was to get the costs down, because it is now 1:1 the production turbocharger as it is used everywhere in the M3 or M4," Roos said when asked by Motorsport-Total.com.
"That is nonsense," says a BMW insider who does not want to be named. "Of course the new turbo is cheaper, but the changeover cost at least a mid to high six-figure sum. For that amount of money, you could have given customers many turbochargers at a cheaper price."
As we understand, the turbocharger change actually requires extensive test sessions with a dedicated testing team, because the change also has to be applied on the dyno. The application is necessary because the tuning of a turbocharger is very complex and the goal is to get as close as possible to the Balance of Performance specifications in order to reach the performance limit. But what actually happened behind the scenes?
Supplier change alerted FIA to BMW in 2024
According to information from Motorsport-Total.com, there was turmoil surrounding the BMW turbocharger during the 2024 GT World Cup in Macau. The German manufacturer had previously applied to the FIA for a supplier change for a part inside the turbocharger because the previous partner could no longer deliver.
In the course of the application, the FIA officials likely became aware that the turbocharger previously used in the M4 GT3 was not a production product, even though the GT3 regulations require it. How the turbocharger nevertheless received approval from the FIA during the car's homologation at the end of 2021 is beyond our knowledge.
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There does not have to be intent behind it, because there are also numerous grey areas when homologating a GT3 car - and theoretically, staff changes at the FIA or differences in interpretation could also have played a role.
BMW threatened with Macau withdrawal due to turbocharger
After the FIA recognized the discrepancy, word is that BMW's participation in Macau in November 2024 was even at risk. It was only after enough members voted in favor of the M4 GT3 being allowed to continue participating in an FIA vote that the green light was apparently given - and Raffaele Marciello almost took the victory for BMW. However, the world governing body demanded a swift change.
This demand was withdrawn a short time later: Since a turbocharger change on a GT3 car has an impact on fuel consumption, combustion, engine maps - and also on the Balance of Performance (BoP) - the FIA turned a blind eye for the time being. BMW was allowed to complete the 2025 season with the familiar turbocharger before the change was requested for the 2026 season.
But does the turbocharger change have an impact on performance? Motorsport Director Roos says that the change in combustion behavior brings "perhaps a slight advantage" in one area, but could also have a "negative" effect in another and is overall "negligible."
The disadvantages of the turbocharger change
Especially at the beginning, it is not that easy to match previous performance with a new turbocharger. This has nothing to do with whether the new part is better or worse, but with a lack of experience.
First, the manufacturer has to get the fine-tuning right so that there are no so-called "overboosts" with the new turbocharger when driving over curbs or bumps - because the wheels spin. This means that the boost pressure specified by the BoP is exceeded - which leads to disqualification.
And then the BoP officials also have to get to know and understand the new technical baseline, which often leads to the car being classified more cautiously in the early stages. Because especially with a fundamental innovation on a car, empirical data is missing - and nobody knows exactly whether the impression corresponds to the facts or whether performance is being deliberately held back.
Change due to sustainable fuels?
One difference is obvious: While BMW was the only GT3 manufacturer to rely on a high Lambda value of 1.1 - and thus a lean fuel mixture - with the previous turbocharger, they are now moving into the range of other manufacturers with 0.9.
This could be due to the now widespread sustainable fuels: Because a lower Lambda value ensures better combustion - and sustainable fuel in particular is considered very difficult to ignite. The disadvantage, however, is that fuel consumption is higher than before due to the lower Lambda value.
