There were quite a few assumptions being made so I purchased an N52 cam and measured it against an N55 cam. The numbers help give a much better idea of how the cam swap will affect an N55. Quite a few of the assumptions in this thread are wrong... including some of my own. Post #67 mixes up the pictures. N55 is left and N52 is right. Post #107 has a lot of assumptions that don't seem to hold true. What I did find with my own measurements was that while the N52 and N55 share very similar exhaust cam profile in their respective engines, there are some other part differences that will produce much different profiles when the cams are swapped.
You can see the previously stated roller ratio of 1.64 can't be true (based upon my measurements). Resulting valve lift would only be 9.27mm. We know the exhaust valve lift for all three engines is 9.7mm so we can use that information to deduce the actual rocker/roller arm ratio for the N55 to be 1.72. It was hard to measure this ratio by hand because as little as 1/64" difference can swing the ratio from say 1.68 to 1.71. The math is simple though and the cam measurements are pretty accurate. 5.65*x=9.7 ==> x=9.7/565 ==> x=1.72. Do the same basic math for the N52 cam and you get a rocker arm ratio of 1.66.
This is important because the ratio play a direct roll in overall valve lift. Multiple the lobe lift provided by the N52 cam by the N55 roller ratio of 1.72 and you get a resulting valve lift of 10.03mm (5.83mm * 1.72 ==> 10.03mm). This is an increase of .33mm lift over stock N55 cam. The exhaust valve will also open earlier and close later. How much? That is not something I plan to try to figure out. It would require more measuring equipment and time than I have.
The general theory would be that more duration and lift out of the exhaust valve could potentially increase whp at high rpm while sacrificing a bit of torque down low. How much? certainly not 100whp. This kind of cam change would be chasing 10whp at best is my assumption. Maybe on an 800whp build you might pick up 50whp... That is reality of making small changes to the exhaust cam especially so with leaving the intake cam stock. Exhaust port restrictions are still there as well.
There are also a few things that need to be considered when doing the swap such as, Spring travel/bind, piston to valve clearance, hydraulic lifter preload/travel, torque on the cam ledge, etc. Most of which might be considered moot since it's a working swap. Stock springs have the travel from what's been measured by others... not too sure what kind of issue might pop up with the lifters.
here is a link to the pics and spreadsheet:
https://drive.google.com/open?id=1R-GaBRBd7Gw6xIL5_GlULuCk3DTbD2O1
Maybe
@CobraMarty or someone like
@MOTIV Motorsport can be so kind as to share some opinions/speculation?