I would not recomend it for street use at all. If your going to do it your going to have to go as far as material will allow you to see the gain. It changes the intake port angle by standing the valve up straighter and making more power. Mostly this is done for small cubic inch engines in heads up classes to get as much hp/ci. Another downfall is when you angle mill .200 your rolling the head over towards the intake side and your headers have to be modified if you dont have room for them to roll with the head.
