Here’s a not-so-quick rundown on the three classes that make up the 2018 International Motor Sports Association WeatherTech SportsCar Championship racing series:

This is the flagship class, and the only one of the three that doesn’t start out as a production car. There are two different Prototypes: those that adhere to the World Endurance Championship “LMP2” model, which stands for Le Mans Prototype 2, and the DPi, which stands for Daytona Prototype international.

The LMP2 is legal for the 24 Hours of Le Mans (as long as it has a Gibson engine, the only powerplant allowed for LMP2 cars by the WEC). The “P2” differs from the more exotic “P1,” which is the top class at Le Mans. The DPi is very similar—in fact, it takes a trained eye to tell an LMP2 from a DPi—but was developed for IMSA competition. Unlike the WEC, IMSA allows for different engines.

There’s the aforementioned Gibson, a normally aspirated 4.5-liter V8; the Mazda, a 2.0-liter turbocharged four-cylinder; the Cadillac, a normally aspirated 5.5-liter V8, down from 6.2 liters in 2017; the Nissan, a 3.8-liter turbocharged V6; and the Acura, a 3.5-liter turbocharged V6. Despite the differences, all the engines are governed by IMSA to around 600 hp. The chassis on both types of car are carbon-fiber monocoque (the original IMSA Daytona Prototypes were tube-framed) with a total weight of just over a ton.

Corvette Racing's Chevrolet Corvette C7.R and drivers Antonio Garcia, Jan Magnussen, Mike Rockenfeller will be a team to watch in the GT Le Mans class at the Rolex 24. LAT PHOTOGRAPHIC

The faster of the two GT classes (GT stands for Grand Touring and signifies a production-based car) is also legal for the 24 Hours of Le Mans, and IMSA purposely doesn’t schedule a race in this class around Le Mans to allow the teams to participate if they want, and most do. The cars participating (BMW M8 GTE, which replaces 2017’s M6 GTLM; Chevrolet Corvette C7.R, Ferrari 488 GTE, Ford GT and Porsche 911 RSR) are factory-backed and have either six- (Porsche and Ford) or eight-cylinder engines, making around 525 hp. The tire brand is not specified, but all the GTLM teams last year used Michelins. (The other two classes must run Continentals through 2018, but that changes to Michelin in 2019 and beyond.)

Scuderia Corsa's Ferrari 488 GT3 will be driven in the Rolex 24 GT Daytona class by Cooper MacNeil, Alessandro Balzan, Gunnar Jeannette and Jeff Segal. LAT PHOTOGRAPHIC

IMSA considers Prototype and GT Le Mans to be “pro” classes, while GT Daytona is “pro-am,” meaning at least one driver for the regular season must be IMSA-ranked as an “amateur.” These cars are built to the global FIA “GT3” specification, legal for dozens of race series worldwide, and are sold by the manufacturers as race-ready models. Cars approved by IMSA include the Acura NSX GT3, Aston Martin Vantage GT3, Audi R8 LMS GT3, BMW M6 GT3, Ferrari 488 GT3, Lamborghini Huracán GT3, Lexus RF GT3, Mercedes AMG-GT3, Nissan GT3-R and Porsche 911 GT3-R. Porsche, Nissan and Acura use six-cylinder engines; Aston Martin uses a V12; Audi and Lamborghini use V10s (basically the same engine) and BMW, Lexus and Mercedes use V8s, all with about 500 hp. GT Daytona cars are slightly lighter than GT Le Mans models, though IMSA reserves the right, through its Balance of Performance regulations, to adjust minimum weight (up or down) to help maintain parity. And finally, Prototype Challenge: This class is missing from the 2018 field, as the aging open-cockpit models—grandfathered in from the American Le Mans Series, as part of the merger between ALMS and Grand-Am in 2014—are now history. That said, IMSA has a support series called the IMSA Prototype Challenge Presented by Mazda, but those are completely different cars that run in their own races, not as part of the WeatherTech series.

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