It's actually a pretty common thing on the 55K's. I don't know what their gains are to the ground or anything but I remember hearing that just on bored valves the engine was able to flow 20% more air in, and 15% more exhaust out. Pretty huge gain, and that IIRC that wasn't including the porting. Which on the heads for sale was extravogent to say the least, they shaved a TON of aluminum out. And I've seen the inside of the heads on the NA's the SRT's and the NA V8's in person, NA55 and 55K in pics. All of them could DEFINITELY use a good port job. The one downside? The set I just saw go used on the MBWorld forum went for $3500...