open downpipe bad for motor? Options

[95st-celica]

well i have had 2 people tell me the same thing this week, and its starting to get me worried. my uncle and father both said that running an open downpipe isnt the greats for the motor. 1) because when its sucks back in cool air it starts to twist the fins on the turbo, and also its not to good for a valves and it will caus them to bend. i know i need an exhaust and thats next on the list, i dont want to drive it around with an open downpipe but right now i have no other choice. i just wanted to see if anyone on here has ever heard of this happening or if it has heppened to them. as soon as i get som money together i will get one put on, but right now theres not much i can do. any comments and suggestions are more then welcome..i would like to hear a couple oppinions on the matter. Thanks