He starts the opening Rugby Championship clash against the Wallabies at Ellis Park at the back of the pack, moved from the flank in a move designed to counter Australia's prowess at breakdown play.
"My role will change slightly in the lineouts and the scrums, but other than that I'll be fulfilling my usual role," Kolisi told a press conference on Friday.
"Playing No.8 at the Sharks certainly helped me, although the role here is different," he said of previous experience at franchise level.
"I'm also not the same type of player as Jasper (Wiese) or Duane (Vermeulen) in terms of my size, so I'm going to give what I can offer."
Vermeulen was a colossus at No.8 for the Boks when they won the last two World Cups and since his retirement Wiese has similarly been physically brutal in his style. However, he is suspended for Saturday's clash.
"The breakdowns are going to be a big area of the game, so myself, (flankers) Marco (van Staden) and Pieter-Steph (du Toit) have important jobs, although that said, the breakdowns are a team effort," added Kolisi, who wins a 94th cap.
Kolisi at flanker gives South Africa more effectiveness at breakdown play, countering Australia's threat, said coach Rassie Erasmus earlier this week.
"The more we prepared, we realised the only time Siya really plays at eight is during scrums, and scrums happen maybe 13 or 14 times a game. General play happens far more. Australia are a huge threat at the breakdown, and Pieter-Steph, Marco and Siya are really strong there," said the coach.
Saturday's clash comes after Australia lost their home series 2-1 to the British & Irish Lions, albeit winning the last Test in Sydney at the start of the month.
South Africa will start as strong favourites but Kolisi cautioned about looking ahead to a potentially stiffer Test against New Zealand later in the southern hemisphere championship.
"The talk in our camp has solely been on Australia. We saw how they played against the British & Irish Lions, and we've been in the position they are now in the past, so it would be foolish to think that they won't throw everything at us," Kolisi said.
