Ramanujacharya was shunted out of Tamil Nadu by the Shivites.He lived in the Hoysala kingdom.He converted many people during his stay(including the Jain King Bittideva to Vaishavism,after conversion,the king was known as Vishnuvardhana(the same king who has built the belur and halebid temples)).Ramanujacharya converted many others and they were the Iyengar's of the karnataka origin.Infact many of the Iyengar's of Karnataka have their origin in Karnataka rather than Tamil Nadu.There may be some people who migrated to Karnataka(including the one's who moved to the old mysore area during the anti brahmin movements of DMK during 60's/70s),but the majority of the iyengars living in the Hassan belt are of Karnataka origin and some of them in the Mandya region were again converted to Vaishnavism by Ramanujacharya when he was in that region.Melukote is a place where you can find many iyengars,where again Ramanujacharya's influence can be seen. To say that iyengar's belong only to Tamil Nadu is wrong.
