"When you play New Zealand franchises you're playing teams with the same philosophy, a philosophy of 'let's play football and may the best team win' but I think the Africans pose a different challenge," Kirwan said.
"They are a bit more brutal, they play to their strengths, they bash you up and are very physical and aggressive, so we've got to be ready for that."
Tasman prop Tim Perry will make his Super Rugby debut in place of Tom McCartney, while Quentin MacDonald replaces James Parsons at hooker.
Liaki Moli will start ahead of Culum Retallick at lock and Steven Luatua shifts to the back of the scrum to replace Peter Saili as Kane Barrett slots in at blindside flanker.
In the backs, Baden Kerr will make his first start in the number 10 jersey in place of Chris Noakes while Taranaki wing Waisake Naholo will make his Super Rugby debut on the left wing.
Ronald Raaymakers, Marty McKenzie and Jamison Gibson-Park are all poised to make their Super Rugby debuts after being named on the bench.
After a 31,014 strong crowd converged on Eden Park for the Blues' first home game of the season last week, Kirwan said he was hoping for another bumper crowd tomorrow afternoon at 4.05pm.
Head to Head: Played 17 Blues 11 Bulls 5 drawn 1.
In Auckland: Played 6 Blues 6 Bulls 0.
Last clash: Round 3, 2012: Blues 29 Bulls 23 at Loftus Versfeld.
Blues
Charles Piutau, Frank Halai, Rene Ranger, Francis Saili, Waisake Naholo, Baden Kerr, Piri Weepu, Steven Luatua, Luke Braid, Kane Barrett, Ali Williams, Liaki Moli, Charlie Faumuina, Quentin MacDonald, Tim Perry. Reserves: James Parsons, Angus Ta'avao, Ronald Raaymakers, Brendon O'Connor, Jamison Gibson-Park, Marty McKenzie, Albert Nikoro.