Vintage-liveried Porsche 911s like this one will share the grid with modern GT3 Cup cars and DPis at the HSR Classic 10 Hour.
Michelin Raceway Road Atlanta hosts the second running of the HSR Classic 10 Hour presented by Mission Foods this weekend, and if the name conjures a continuous ten-hour green flag like Daytona or Sebring, recalibrate. Groups A/B, C and D each contest three 42-minute heats spread across Saturday and Sunday, adding up to something close to ten symbolic hours of combined track time without a single car ever turning an actual ten-hour stint. That’s not a shortcut for marketing purposes. It’s the only sensible way to run a grid spanning five decades of chassis technology on the same racetrack at the same time.
Consider what’s actually sharing pavement this weekend. David Agretelis returns in the 901 Shop’s 1972 Porsche 911 S/T, a car built around drum-adjacent brake thinking and period-correct tire compounds. His 901 Shop stablemate Ben Myers rolls out a 2017 Porsche 991.2 GT3 Cup car running carbon brakes and modern slicks, built in an era where Porsche’s factory-adjacent GT customer program is currently fighting over balance-of-performance in IMSA’s premier GT ranks. Pierce Marshall and Eric Foss bring a 2017 Cadillac DPi prototype that once raced wheel to wheel with factory-backed manufacturer programs in real IMSA endurance events. Put all three on a racetrack for an uninterrupted ten hours and you’re not running a tribute event anymore, you’re running an insurance claim. Splitting the field by era and capping heats at 42 minutes keeps brake fade, tire degradation and driver fatigue inside limits fifty-year-old chassis were never engineered to survive, while still letting HSR call the aggregate distance a “10 Hour” that echoes the endurance classics it’s built to honor. We’ve covered why a genuine 24-hour format is considered motorsport’s toughest endurance test elsewhere on this site; the Classic 10 Hour borrows the branding, not the punishment.
That branding exercise is deliberate. The Classic 10 Hour is round two of four “tribute events” inside the HSR Classic Endurance Championship presented by Mission Foods, a points series built specifically so historic and vintage sports cars can race under the names of America’s longest-running endurance classics: Watkins Glen’s 6 Hour heritage in June, Road Atlanta’s 10 Hour this weekend, Daytona’s 24 Hour in November and Sebring’s 12 Hour in December. It’s the first points championship of its kind for vintage cars in the U.S., and it exists in this form because HSR, founded at Road Atlanta in the mid-1970s, folded into IMSA’s ownership in 2022, inheriting the sanctioning muscle, live timing and ticketed-weekend infrastructure of a professional championship, the same infrastructure IMSA has been expanding through outside partnerships that reach well past the racetrack fence.
The championship math is what turns this weekend into more than a parade lap. Agretelis and the Marshall/Foss Cadillac crew both won their classes at the June opener at Watkins Glen, and both were also inaugural 2025 Classic Endurance Cup champions in those same categories, meaning they’re defending real titles, not just chasing a trophy. Marshall and Foss are specifically chasing a distinction of their own: becoming the first repeat winners of the Classic 10 Hour outright, in just its second year of existence. A repeat for any of the Glen winners this weekend hands them a psychological edge heading into the final two rounds at Daytona and Sebring.
None of this happens in isolation from the rest of Road Atlanta’s calendar. The Classic 10 Hour headlines a five-day production called the HSR Fall Historics, which stacks the B.R.M Endurance Challenge, the SascoSports International-American Challenge, the Mission GT Challenge and the 90-minute HSR Prototype Challenge around it, plus doubleheader sprint races for every Run Group. That’s a lot of vintage metal turning laps for a paying, ticketed crowd, and it’s proof HSR’s tribute-race concept is being run and marketed like a genuine professional weekend rather than a car-club track day with a fancier name.
Saturday’s card opens with the combined Groups A and B heat at noon Eastern, worth watching for how a 1970s GT car and a modern Cup car handle braking zones and closing speeds while sharing the same 42 minutes of green flag. The result that actually decides anything arrives Sunday afternoon, when each group’s final heat starts at 1:15 p.m. Eastern and the combined times across all three segments determine the Classic 10 Hour winners outright. Down in IMSA’s modern-day record book, the same weekend finds the GTP class fighting a math problem of its own, with Acura trying to close a significant points gap with only two championship rounds remaining, a reminder that this is a big month for IMSA-sanctioned racing at both ends of the calendar. From Road Atlanta, the HSR Classic Endurance Championship heads to Daytona in November for its 24 Hour tribute round, the closest thing this series has to a season-defining stage before Sebring closes the books in December.
About the Author
