  We extend our recent derivation of the time evolution equations for the
energy content of magnetic fields and turbulent motions for incompressible,
homogeneous, and isotropic turbulence to include the case of nonvanishing
helicity. These equations are subsequently numerically integrated in order to
predict the present day primordial magnetic field strength and correlation
length, depending on its initial helicity and magnetic energy density. We find
that all prior analytic predictions for helical magnetic fields, such as the
epoch when they become maximally helical and their subsequent growth of
correlation length L ~ a^{1/3} and decrease of magnetic field strength B ~
a^{-1/3} with scale factor a, are well confirmed by the simulations. An
initially fully helical primordial magnetic field is a factor 4 10^4 stronger
at the present epoch then its nonhelical counterpart when generated during the
electroweak epoch.
