I used them on my 440 with TTIs.They lasted about a week before they leaked.The cheap white ones that came with the TTIs lasted about 4 years.Now I use Mr Gasket Ultra seal.Mine have been on 4 years now.No leaks.Had them on the kids sb truck.I even took the headers off and reused them and they still sealed.The other kid has them on his 413 with headers.They are at least 10 years old.Reused them once and they are still sealed.Rocky