I know that I have built and tuned plenty of older Chevy Camaros and such, and they ran ok without exhaust to get the down to the exhaust shop, just don't get on it until you get the exhaust.... Now one other thing, is possibly be prepaired to retune some after having the exhaust installed, as it will change your back preasure and can also cause some issues that way, but other than that you should be ok to run it up with no exhaust for a short bit...