I would not run a 52T spur with a big motor. It will be geared too steep and your truck will wheelie out of control (annoying). 18/52 will not even mesh properly. I would gear taller with a 47T Spur.
Check this:
http://www.hpiracing.com/graphics/instr/savagegears.jpg
Check this:
http://www.hpiracing.com/graphics/instr/savagegears.jpg