van der Grinten map projection

I`m trying to understand a map produced by MapQuest, which I want to
use as a backdrop for a model where I will have to place real-world
locations (based on Lat/Long) on a grid for display.

The best I can tell, MapQuest uses the van der Grinten map
projection. I found the equations to convert from Lat/Long to
Cartesian coordinates (x,y) at
http://mathworld.wolfram.com/vanderGrintenProjection.html . However, I
don`t seem to get numbers than make sense. Some of my calculations:

For Lat/Long 51N, 65.8W, I get x = 2.0692, y = 6.4904

For Lat/Long 34.3N, 65.8W, I get x = 18.1152, y = 1.2581.

but they are both at 65.8W.

Any help or pointers or more explicit links would be
appreciated.

Thanks, Alan