I have the Energy Suspension motor mounts in my car with Flowtech headers. I had to dimple the header and grind a small amount of metal off of the top of the mount to get 3/16" clearance.
When you get into the throttle the motor will flex in a direction that acts to close that gap. The harder you get into it the more it moves. The mounts are really stiff and there is very little motor movement. After 3500 miles there has not been any contact between the header and the mount. I only get into the throttle about every 5 minutes when I am driving it. Hope that helps.
FFR 2772, Torch Red, Artic White Stripes, Image Wheels, 302EFI, 3.55 gears, Power Steering and Power Brakes