  We show the presence of CVs with orbital periods in the range 3.5-7 h and
mass ratios q=M2/M1 above the critical values for dynamically stable mass
transfer. We explore whether the magnetic fields produced in the secondaries
alter the theoretical mass ratio limits allowing dynamical stability. Since
magnetic fields change the specific heats and the polytropic exponent gamma of
the gas in the convective envelope, the mass-radius adiabatic exponent xi_ad
also changes. We find that turbulent magnetic fields can produce 10% less
restrictive critical q-profiles while large-scale toroidal and poloidal fields
have smaller effects. Thus, magnetic fields alone do not account for the
stability of all the anomalous CVs. However, we found that the small variations
of xi_ad induced by solar-type magnetic cycles explain the amplitudes of the
cyclic accretion luminosity variations shown by several CVs.
