Milling the head.............
There are several advantages to milling the head on the new edition Whizzers, but most importantly it increases the head surface mating area. Most [if not all] have a very small area between the 10 MM bolts and the combustion chamber. The combustion chamber walls are tapered, and the area between the 10 MM bolts and the combustion chamber increases as the head is milled. Almost always [approx. 95%] the head gasket leaks in this area, and most often on the exhaust side.
While it is true, increased compression does add extra power, it is most noticable at lower speeds, and the biggest increase is torque, not HP.
The most common comment I hear about Whizzers is the major difference between the original motor and the new edition version. Everyone that owns or rides an original Whizzer notices the low end "grunt" [torque] and how much easier it is to put the bike in motion. There are three reasons this is so, first the compression ratio, and secondly the combustion chamber design, and lastly the "flywheel" action. It would be next to impossible to duplicate the original flywheel, but the head is another matter.
The original head was different is several ways, but with a little effort the new generation version can be made to closer match the "torque" of the vintage motor. In order to explain the needed changes it is important to identify the various versions. The WC-1 heads were very similar to the "H" & "J" motors of yesteryear, and in fact the very rare early NE head was a close copy of the WC-1 head but had the "island" machined out for better flow. I guess it would be a good time to mention the early NE head was really strong [did I mention very rare?], but when the "island" was removed the area next to the 10 MM head bolt was reduced too much, and often resulted in a leaky head gasket. I won't spend a lot of time discussing the early head because they are so rare, but milling this version increased the metal surface between the combustion chamber and the 10 MM bolts and reduced the need to replace the head gasket as often.
The next generation NE head not only needed to be milled but a lot of time needed to be invested in trying to "smooth" out the maze of crazy angles and sharp edges. Sadly this is the most common head used on the NE motor. As a rule I end up removing a lot of metal from the combustion chamber to blend the walls for better flow, and normally I mill these heads at least .065" ~ .070" to make up some of the compression lost via re-shaping the chamber.
A few, not many, of the NE motors sported a special head. I call it special because it is "almost" identical to heads I designed & tested in 2006 [except for the oval shaped valve pockets], however I consider it the best head Whizzer offered for the NE motor [did I mention they only made a few?].
For the few that express concerns about the bottom ends ability to survive milling the head. Of the 4 known crankshaft problems, 2 were "twisted" [caused by using an "impact" wrench], and 2 were snapped off because of early tests with CVT drive systems [I think the flywheel was doing at least 40 MPH traveling down the road without the rest of the motor]. I have one motor with over 165 pounds of compression, and the crankshaft is not something I worry about.
The cost to have the head milled by the average machine shop is almost always over $75.00. Over the past few years I re-worked the combustion chamber, milled the head, and shortened the head bolts for less than half that amount. Because of the many hours, Dremel stones, sanding drums, and sanding disks needed to make the modifications my rate will increase on March 1st.
This information isn't intended to "bash" anyone, company, or vendor.
Have fun,