In 1966 he returned to Porsche for a comeback in the World Sportscar Championship, as Porsche started a serious effort there. Following several podium finishes with the still underpowered two liter Porsche 906 and later models, he won the 1968 24 Hours of Daytona in a 907 as well as the Sebring 12 Hours again, now together with Swiss Jo Siffert. The overall win of the 1000km Nürburgring always eluded him, even though Herrmann had taken part in each of these races at the Nürburgring since they were introduced in 1953, and had finished second three times in a row from 1968 to 1970, behind teammates Jo Siffert and/or Vic Elford.
