I have read comments from a guy on another forum that put one on his 409 and he absolutely loves it from the git go. That was about a year ago and he has expierienced no problems to date and say's the response is great and fuel mileage is good also. He said that the self tuning feature worked great on his built 409 and did not need to do any alterations. He highly recommend the system. Just to note his car has a closed hood also.