https://phys.org/news/2019-02-spacex-raptor-chamber-pressure-russia.html > The RD-180 was the product of the Soviet-era Energia rocket program, which sought to create a super-heavy launch vehicle that would take the reusable Buran spacecraft (Russia's version of the Space Shuttle) into orbit. While the program was discontinued, the engine survived and was even imported to the US, where it became part of Lockheed Martin's Atlas III rocket and United Launch Alliance's Atlas V. > For decades, the RD-180 and its predecessor (the RD-170) held the record for combustion chamber pressure, ranking in at 26.7 MPa (3,870 psi) and 24.52 MPa (3,556 psi), respectively. However, three days after Musk initially tweeted about the Raptor's performance results, he declared that the chamber pressure had "reached 268.9 bar" – which works out to 26.89 MPa (3,900 psi), thus establishing a new record by about a 1 percent margin.