I took my car to a local performance shop to have my 4-1 header put on. After a few hours of work i was told by the mechanic that i needed a flex pipe put on in order for the header to bolt up underneath. He said to take it to an exhaust shop and tell them i need a flex pipe put on at the same my header is put on. As anyone had the same trouble?

Edit: The car is a 98 Integra GSR