Why do Japanese car engines have a 280 HP limit on older models?

The 'gentleman's agreement' was a voluntary industry pact among Japanese manufacturers (1989-2004) to rate all production sports car engines at 280 PS (276 HP) regardless of actual output. This was partly a response to concerns about escalating performance numbers. Cars like the Skyline GT-R and Supra Turbo had actual dyno-measured outputs of 300-330 PS despite the 280 PS factory rating.