  We study cosmological models with modified Chaplygin gas (in short, MCG) to
determine observational constraints on its EoS parameters. The observational
data of the background and the growth tests are employed. The background test
data namely, H(z)-z data, CMB shift parameter, Baryonic acoustic oscillations
(BAO) peak parameter, SN Ia data are considered to study the dynamical aspects
of the universe. The growth test data we employ here consists of the linear
growth function for the large scale structures of the universe, models are
explored assuming MCG as a candidate for dark energy. Considering the
observational growth data for a given range of redshift from the Wiggle-Z
measurements and rms mass fluctuations from Ly-$\alpha$ measurements,
cosmological models are analyzed numerically to determine constraints on the
MCG parameters. In this case, the Wang-Steinhardt ansatz for the growth index
$\gamma$ and growth function $f$ (defined as $f=\Omega_{m}^{\gamma} (a)$) are
also taken into account for the numerical analysis. The best-fit values of the
equation of state parameters obtained here are used to study the variation of
the growth function ($f$), growth index ($\gamma$), equation of state parameter
($\omega$), squared sound speed $c^2_{s}$ and deceleration parameter with
redshift. The observational constraints on the MCG parameters obtained here are
then compared with those of the GCG model for viable cosmology. It is noted
that MCG models satisfactorily accommodate an accelerating phase followed by a
matter dominated phase of the universe. The permitted range of values of the
EoS parameters and the associated parameters ($f$, $\gamma$, $\omega$,
$\Omega$, $c^2_{s}$, $q$) are compared with those obtained earlier using other
observations.
