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A Guide to IMSA Sports Car Racing Classes

International sports car racing attracts a large, passionate fanbase, as well as multiple manufacturers. The best test of a race car’s endurance is a 24-hour race like Le Mans or Rolex 24 at Daytona. The favored addition of multiclass racing during these events adds excitement and interest for spectators. But some people wonder why exotic prototype entries compete on the track with the slower, larger, and heavier GT cars, such as Mercedes, Corvette, and other popular sports car brands. The reason is that these different types of cars are racing for victories and championships within their own group of competitors, and it’s thrilling to watch faster drivers thread their way through slower traffic.

The premier multiclass racing organization in North America is the International Motor Sports Association (IMSA). IMSA’s first race of its 2023 schedule was at the Daytona International Speedway, and the Rolex 24 began the 11-race WeatherTech SportsCar Championship. The Rolex 24 saw 61 competitors start the 24-hour race as teams fought to win a Rolex watch by finishing first in one of the five racing categories: Grand Touring Prototype (GTP), Le Mans Prototype 2 (LMP2), Le Mans Prototype 3 (LMP3), Grand Touring Daytona PRO (GTD PRO), and Grand Touring Daytona (GTD). Here’s an explanation of each of those classes: 

The GTP hybrid prototypes require a large technical team to maximize performance and reliability. The team prepared the No. 1 Cadillac for a pre-race warm-up.

Style of Car: Grand Touring Prototypes

The GTP entries must comply with the international LMDh Hypercar technical regulations. Approval allows any manufacturer who produces more than 2,500 vehicles annually worldwide to build and race a Hypercar prototype. Acura, BMW, Cadillac, and Porsche were approved to compete in this international class in 2023; Lamborghini will join in 2024. These manufacturers can compete at Le Mans and other international events. Each brand adds their own wind tunnel-enhanced body design to one of the four approved chassis constructors. The manufacturers are ORECA for Acura, Porsche with Multimatic, Lamborgini with Ligier, and Dallara (being used by BMW and Cadillac).

Engine choices vary, but all competitors are required to use a 50kw (67hp) hybrid power unit. Acura is powered by a 2.4-liter (146ci) twin-turbo V-6, and Cadillac uses a 5.5-liter (336ci) non-turbo V-8. BMW runs a 2.4-liter (146ci) twin-turbo V-6, and Porsche has a 4.6-liter (280ci) twin-turbo V-8. The combined horsepower of these engines and hybrid units ranges from 643 to 697 horsepower. Each prototype is priced at $2,200,000-plus, and that does not include spare parts or crew expenses. Performance is adjusted with the Balance of Performance (BoP) process by IMSA. BoP regulates horsepower, weight, and aerodynamics to maintain competition equality. The No. 60 Meyer Shank Acura ARX-06 started first and was the race winner. Its fastest race lap was 01:35.616 at 134.036 mph.

Le Mans Protoype 2

The LMP2 category is powered by a 4.2-liter (254ci) 500-hp V-8 and a chassis from Ligier, Multimatic, Dallara, or ORECA. The ORECA chassis is preferred by most of these competitors. Its homologated price is $506,000. The No. 55 Proton Competition ORECA LMP2 started 19th, and finished first-in-class and 7th overall. Its fastest race lap was 1:39.606 at 134.036 mph.

Le Mans Protoype 3

The LMP3 is an entry-level prototype race car. It is powered by a 5.6-liter (342ci) Nissan V-8 truck engine that produces 450 horsepower. The No. 17 AWA LMP3 started 20th, and finished first-in-class and 15th overall. Its fastest race lap was 1:43.542 at 123.776 mph.

The pits were busy during practice and qualifying. A Porsche 963 GTP and the Corvette GTD PRO teams made final adjustments before returning their cars to the track.

Style of Car: GT

The IMSA GTD class mimics the worldwide FIA SRO GT3 racing category. The main difference between the GTD PRO and GTD is the driver’s FIA ranking (bronze, silver, gold, or platinum). The GT3 cars are identical. The GT3 class was developed by Stephane Ratel, president of SRO Motorsports Group, and it received FIA approval in 2006. It has been a worldwide success, with grids exceeding 40 entries, and typically the No. 1 to No. 20 qualifying positions are separated by 0.9 second. Audi, Porsche, Lamborghini, Ferrari, Aston Martin, Callaway Corvette, BMW, Mercedes-Benz, Ford GT, McLaren, and Bentley have all competed in GT3 since 2006.

GTD Classes

When Grand-Am merged with the American Le Mans Series in 2014, the GTD class was created. It blended Grand-Am GT entries with GT3 cars to form one class. Today, IMSA follows the FIA Group GT3 format and rules, including dividing GTD into two categories: GTD PRO and GTD. The amateur class allows only bronze- and silver-rated drivers to compete; GTD PRO is for the experienced gold- and platinum-rated drivers.

In GTD, the No. 27 Heart of Racing Team Aston Martin Vantage GT3 qualified 37th, and finished first in GTD and 16th overall. Its fastest race lap was 1:46.078 at 120.816. In GTD PRO, the No. 79 WeatherTech Racing Mercedes-AMG GT3 qualified 31st, and finished first and 17th overall. Its fastest race lap was 1:45.51 at 121.431 mph.

These IMSA/ACO/FIA multiclass racing categories are unique, and the heritage of this system can be traced back to Le Mans, France. In 1923, the Automobile Club de l’Quest (ACO) held the first multiclass 24 Hours du Mans in the French village of the same name. The first 24 Hours of Daytona was held in 1966, and both are now premier international racing events.

Acura Racing

The pole-position Meyer Shank Racing/Curb Agajanian Acura ARX-06 hybrid GTP quickly pulled away from the other GTP competitors.
The Acura GTP’s hot pace helped it to quickly begin lapping the slower competitors, like this Ferrari 296 GT3 GTD (green placard). The Ferrari was eliminated in a late-race accident after completing 655 laps.
Racers Edge Motorsports competed with this No. 93 Acura NSX GT3 in GTD. The team qualified fourth and started 31st. They finished sixth-in-class and were 26th overall.
The race-winning No. 60 Acura hybrid comlpeted 783 laps at the end of 24 hours and was 4.190 seconds ahead of the second-place Acura when the checkered flag fell on Sunday.
The No. 13 Duqueine D08 qualified seventh in LMP3 (orange placard) and was 11.791 seconds and 10.447 mph slower per lap than the Acura GTP. Here, it was passed by the Wayne Taylor Racing No. 10 Acura ARX-06 that finished the race in second position.

Cadillac Racing

Cadillac Racing’s No. 01 V-LMDh hybrid (black placard) maintained constant pressure on the leading Acura during the chase for overall 24-hour victory. Drivers Renger van der Zande/Scott Dixon/Sébastien Bourdais finished third overall, a scant 9.630 seconds behind the winning Acura.
This normally aspirated flat-plane-crank 5.5-liter V-8 No. 02 Cadillac GTP was fourth overall, 11.176 seconds behind the winner. It was a pleasure hearing this engine scream when it was wide open on the Daytona banking.

Porsche Racing

This Penske Porsche 963 finished eight laps behind the winning Acura. It experienced a mechanical issue during the race but crossed the finish line seventh in GTP and 14th overall.

BMW Racing

GTP No. 25 BMW P66/3 4.0L hybrid qualified eighth overall and completed 652 laps to finish 48th and ninth in GTP.
BMW raced its new No. 95 Turner Motorsport M4 GT3 in the GTD PRO class (red placard). They qualified seventh and started 47th, but did not finish after 635 laps because of a broken power steering unit.
This No. 96 Turner Motorsport BMW M4 GTD (green placard) qualified 12th and started in 44th position. They finished 17th-in-class and 44th overall.

Mercedes-AMG Racing

This GTD PRO WeatherTech Racing Mercedes-AMG GT3 (red placard) was driven by Daniel Juncadella/Maro Engle/Cooper MacNeil/Jules Gounon. The team qualified first in GTD PRO and was 12.753 seconds slower per lap than the pole-winning Acura GTP.
This GTD PRO WeatherTech Racing Mercedes-AMG GT3 (red placard) was driven by Daniel Juncadella/Maro Engle/Cooper MacNeil/Jules Gounon. The team qualified first in GTD PRO and was 12.753 seconds slower per lap than the pole-winning Acura GTP.

Corvette Racing

Corvette Racing began competing with its C8.R GTLM Corvette in 2020. GM is building 20 customer C8.R GT3 cars that will race in 2024, priced at $740,000. This GTLM entry was altered to fit into the IMSA GTD PRO category for 2023. It qualified fourth and finished second behind the front-engine Mercedes.
Corvette Racing practiced pit stops during qualifying for the Rolex 24. The team executed precision pit stops, which helped their overall racing performance.

Aston Martin Racing

This photo of the No. 27 Heart of Racing Team Aston Martin Vantage provides a good look at the complexity of a GT3/GTD race car. It won the GTD category and finished 16th overall.
The Aston Martin No. 64 was powered by a twin-turbo 4.0-liter V-8 and qualified fifth in GTD PRO, and finished ninth-in-class and 45th overall after completing 674 laps.

Ferrari Racing

This new Risi Competizione Ferrari 296 GT3 qualified ninth in GTD PRO but did not finish after damaging its floor in an off-course incident during the race. It completed 349 laps.
The No. 21 AF Corse aFerrari 296 GT3 (green placard) was identical to the No. 62 Ferrari raced in the PRO category. It qualified 17th in GTD and finished 19th-in-class and 47th overall.

McLaren Racing, Lexus, and Lamborghini Racing

The Inception Racing No. 70 McLaren 720S GT3 qualified sixth in GTD and started 34th. The Inception Racing team drivers Marvin Kirchhöfer/Brendan Iribe/Frederik Schandorff/Ollie Millroy finished third in GTD and 20th overall.
Lexus first raced this RC F in 2017, and here it is at the 2019 Rolex 24 Hours. The Vasser Sullivan team raced two of them at this year’s Rolex 24. No. 14 RC F GT3 competed in GTD PRO and No. 12 in GTD. The PRO car finished third-in-class while the GTD finished fifth.
The second-place Acura ARX-06 blasted past this No. 42 NTE Sport Lamborghini Huracan GT3 EVO2 on the high banks of Daytona. The Lamborghini did not finish due to a broken oil tank after completing 356 laps. Passing slower cars is always a challenge for faster cars.

Photos are courtesy of Tyler Thurn

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