  We present time-resolved spectroscopy and photometry of the double-lined
eclipsing cataclysmic variables AC Cnc and V363 Aur (= Lanning 10). There is
evidence of irradiation on the inner hemisphere of the secondary star in both
systems, which we correct for using a model that reproduces the observations
remarkably well. We find the radial velocity of the secondary star in AC Cnc to
be K_R = 176 \pm 3 km/s and its rotational velocity to be v sin i = 135 \pm 3
km/s. From these parameters we obtain masses of M_1 = 0.76 \pm 0.03 M_sun for
the white dwarf primary and M_2 = 0.77 \pm 0.05 M_sun for the K2 \pm 1V
secondary star, giving a mass ratio of q = 1.02 \pm 0.04. We measure the radial
and rotational velocites of the G7 \pm 2V secondary star in V363 Aur to be K_R
= 168 \pm 5 km/s and v sin i = 143 \pm 5 km/s respectively. The component
masses of V363 Aur are M_1 = 0.90 \pm 0.06 M_sun and M_2 = 1.06 \pm 0.11 M_sun,
giving a mass ratio of q = 1.17 \pm 0.07. The mass ratios for AC Cnc and V363
Aur fall within the theoretical limits for dynamically and thermally stable
mass transfer. Both systems are similar to the SW Sex stars, exhibiting
single-peaked emission lines with transient absorption features, high-velocity
S-wave components and phase-offsets in their radial velocity curves. The Balmer
lines in V363 Aur show a rapid increase in flux around phase 0 followed by a
rapid decrease, which we attribute to the eclipse of an optically thick region
at the centre of the disc. This model could also account for the behaviour of
other SW Sex stars where the Balmer lines show only a shallow eclipse compared
to the continuum.
