Problem exhaust drone: Solution 1/4 wave, or Helmholtz resonator?

[Bean]

Have the closed of part of the pipe as a sleeve going over the rest of the construction. That way you'll be able to adjust the length until you get it right.
It will take quite some time testing but honestly no amount of calculations will get it right. The calculations will only give you a starting point, as there are way to many factors involved which you can only approximate for.