2017 IMSA GT Racing Rules

The 2017 Daytona 24 hours has an interesting field and mix of cars, especially in the GT class. Although I have been involved in racing sports cars for over 40 years, I found the rules for the GT classes quite confusing this year. Gone are the days of Group 4 (Porsche 934) and Group 5 (Porsche 935), where things seemed more simple. Today there seem to be confusing sets of rules on both sides of the Atlantic and worldwide as regards GT racing. It was not clear to me, which cars could run in IMSA, and which ones could run at Le Mans or the FIA GT championship, or if there was any cross-over at all. To try and make some sense of it all, I took some time at the 2017 Daytona 24-hours to sit down and talk to my brother, Mark Raffauf, who is the Senior Director of Series Platforms for IMSA, about the 2017 IMSA GT racing rules.

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Mark has been involved in sports car racing since the 1970s. He is a long-time employee of IMSA, being possibly the longest tenured employee. He has held many positions at IMSA including President, Chief Steward, Yearbook Editor, Series director and Competition Director.

Although our discussion concerns Porsche RSR GTLM and Porsche GTD (GT3) cars mostly, the Daytona 24-hours race features GT cars from many different manufacturers, including Ferrari, Ford, Chevrolet, Lamborghini, Honda (Acura), Mercedes, Toyota (Lexus).

What follows is an edited version of our conversation, which hopefully helps to clear up some details:

Martin Raffauf: In IMSA there are GTLM class cars, which include the new RSR Porsche, Corvettes, BMWs, a Ferrari 488 GTLM and of course the Ford GT, as well as GTD cars which has a whole other mix of cars, including a Porsche GT3. What is the basic difference between these cars?

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Mark Raffauf: Well, GTD (or GT Daytona) is a class based on the FIA GT3 car. These cars are based on production cars with a minimum production level specified. The cars are homologated by the FIA, and IMSA will make modifications with power and weight (Balance of Performance – BoP) to equalise the cars and conform to a desired lap time at US circuits, about 4 seconds slower (at Daytona) than GTLM. GTLM is a class created by the FIA and ACO (Automobile club de L’Ouest) which are highly modified, somewhat production based (meaning more technical waivers are allowed on an individual basis in the vehicle homologation) GT cars. In IMSA, GTLM are in effect, ‘factory backed’ cars, making this a manufacturer class. GTD cars are private entries, albeit with quite a bit of manufacturer assistance.

Martin Raffauf: So, the GTD cars are homologated by the FIA, and the GTLM cars are basically free and open?

Mark Raffauf: No, not exactly, the GTD car is an FIA GT3 car that is homologated by the FIA. There are technical waivers and exceptions to the basic homologation by the FIA, which are controlled by a written homologation process. IMSA basically accepts the FIA homologation, and adds some safety rules, as well as some potential BoP changes. The GTLM cars are also homologated by the ACO and FIA under a more specific process tailored to each make and model. IMSA accepts the car as homologated with minor exceptions, again BoP-based. So, the GTLM cars are also regulated via homologation, and are not ‘free.’

Martin Raffauf: Does IMSA accept any FIA GT3 car as GTD and any ACO approved GT car as GTLM?

Mark Raffauf: For the most part yes, although we run our own engineering tests on GTLM cars prior to acceptance at facilities in North Carolina (engine dynos at the NASCAR technical centre and Windshear wind tunnel). Only large volume auto manufacturers who are producing significant volumes of these models and marketing their brands to the public, are eligible. ‘Specialty’ cars are not accepted, though there are some with National homologations in GT3 in overseas series.

Martin Raffauf: Why would you as IMSA, have to change the cars from an as homologated car, that is, to have different BoP than say Le Mans for example?

Mark Raffauf: The main reason is, we are the only series worldwide that runs four classes of cars. Prototype (DPI/LMP2 IMSA), PC, GTLM and GTD. So, in general we attempt to keep a three to four second gap between classes for our races, to provide a consistent show for the fans. We dyno and wind tunnel test our cars (except PC (spec) and GTD) to help us set the proper parameters. For example, at Daytona, we would like a four-second gap in lap times between GTLM and GTD, so the BoP is adjusted accordingly. We must also take into account that in the GTLM class the tyres are ‘free’ (Ed: all cars in the class today are running on Michelin tyres), while the GTD class uses the series tyre, which is Continental.

Martin Raffauf: So, both IMSA GTD and GTLM cars could run at Le Mans?

Mark Raffauf: Well, no. GTLM cars with some minor modifications (BoP) could and do run at Le Mans (reference the Ford GT/Corvette/Porsche and Ferrari 488 in 2016). GTD cars, being GT3, are not WEC legal cars. GTD cars can run in various FIA GT3 championships in Europe and Asia with some potential minor BoP changes, as each of those series also use minor BoP adjustments for their specific needs

Martin Raffauf: So why does a company like Porsche build cars for both classes, GTLM and GTD?

Mark Raffauf: They use GTLM as a factory car in IMSA, and sell the GTD cars to customers.

Martin Raffauf: How does a company like Porsche approach IMSA with regards to rules?

Mark Raffauf: Well, they don’t really. The manufacturers like Porsche, work with the FIA and ACO to get their cars homologated. We, as IMSA, do not really have much to do with the actual homologation process. Once the car is homologated then we would be involved with doing our engineering tests, specifically on the GTLM (as well as Dpi).

Martin Raffauf: Thank you, this has been very helpful and enlightening.

Mark Raffauf: You are welcome…my pleasure.

Written by: Martin Raffauf
Images by: Martin Raffauf