IMSA has set participation requirements for GS class manufacturers competing in next year’s Continental Tire SportsCar Challenge, in the wake of the introduction of GT4-spec machinery.

Aimed at “providing more flexibility and diversity of vehicles in the class,” only manufacturers that that are Official Automotive Partners with approved vehicles will be eligible to compete for the manufacturers’ championship.

Manufacturers that have already entered into agreements in the WeatherTech Championship will be included as part of IMSA’s “overarching partnership agreement.”

IMSA, however will also permit approved GS cars from manufacturers not electing to enter into partnerships to compete for race victories and driver and team championships, but those teams would not be eligible for the year-end points fund or manufacturers’ championship.

Official Automotive Partners, meanwhile, will receive “name and logo recognition across a variety of activities and reports” unlike non-automotive partners, according to the sanctioning body.

A number of existing GS manufacturers are already IMSA Automotive Partners, including Ford (Mustang GT4), Porsche (Cayman GT4 Clubsport MR) and BMW (M4 GT4), although other GT4 automakers, including McLaren, do not currently have agreements.

IMSA will only accept GT4 cars from “mainstream or select small volume” automotive manufacturers, with vehicles from bespoke race car manufacturers, such as SIN and KTM, not being eligible.

The move is similar to what IMSA established in the GT Daytona class, prior to 2016, when it allowed non-Automotive Partners to compete, but without branding or the cars being eligible for the manufacturers championship.

An Automotive Partnership is currently required for participation in the GTD class.

The changes to GS come after a series-low single-digit car count for the majority of the season, which saw as few as four cars take part in a race this year.

IMSA has also confirmed other changes to the series for next year, including the establishment of a year-end points fund, and a reduction in the number of at-track days for competitors.

Teams forgoing the optional Promoter Test Day will now be able to have their cars scrutineered at a later time in the weekend, which will trim at least five at-track days from the season compared to 2016.

Competitors will also see an increase in practice time by 35 minutes on most weekends, despite the reduction of the majority of races from two hours and 30 minutes to two hours.

As previously revealed, Platinum-rated drivers have been banned from competing in the series, despite no Pro-Am enforcement in either GS or ST classes.

The 2017 season kicks off with a four-hour enduro at Daytona on Jan. 27.