I tuned a vehicle using a Dart cylinder head. All I can say is the motor dropped a valve within 7 days using Dart's valvetrain. I don't know if the issue had to do with the kid not knowing how to drive or if it was a failure in the head. I was not very impressed with the hp gains made by using the head over a traditional head, however it was only a 1.8L n/a setup using mild compression & a crappy GSR DC sports header & restrictive exhaust system.