The GS 400 is called that because of the 400 cubic inch engine. That being said, that may not be the most accurate name. Many hold the belief that the horsepower rating was stated lower, in hopes of keeping insurance premiums lower, too. With 340 horsepower on record, it may have had more than that. That horsepower was an increase (by as much as eight percent) and the peak torque was higher than previous models, too.
There were many great additions to the GS 400 over previous models. For example, it was offered as a hardtop and a convertible. A three speed turbo Super Turbine 400 automatic transmission was available. If that sounds unique, it is, as it’s considered to be one of the top automatic transmissions built, period.
Motor Trend magazine’s comments at the time still hold true today: “Power is all there for street running, especially when you put your foot in it and open all four barrels. Downshifting acceleration really puts you back in your seat. One distinct characteristics of the engine seems to be its smoother idle with a big cam. It’s not nearly as rough as similar super cars with similar grind cams.” Indeed, the GS 400 shows how Buick added to and improved their vehicles year after year.