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 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.

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.

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 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.

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.

Photos are courtesy of Tyler Thurn

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