  We calculate explosive nucleosynthesis in Chandrasekhar mass models for Type
Ia Supernovae(SNe Ia) to obtain new constraints on the rate of matter accretion
onto the progenitor white dwarf and on the ignition density of central carbon
deflagration. The calculated abundance of the Fe-group neutron-rich nuclei is
highly sensitive to the electron captures taking place in the central layers.
The yields obtained from a slow central deflagration, and from a fast
deflagration or delayed detonation in the outer layers, are combined and put to
comparison with solar isotopic abundances. We found that (1) to avoid too large
ratios of $^{54}$Cr/$^{56}$Fe and $^{50}$Ti/$^{56}$Fe, the ignition density
should be as low as \ltsim 2 \e9 \gmc, and that (2) to avoid the overproduction
of $^{58}$Ni and $^{54}$Fe, either the flame speed should not exceed a few % of
the sound speed in the central low $Y_e$ layers, or the progenitor star has to
be metal-poor compared with solar. Such low central densities can be realized
by a rapid accretion as fast as $\dot M$ \gtsim 1 $\times$ 10$^{-7}$M$_\odot$
yr$^{-1}$. In order to reproduce the solar abundance of $^{48}$Ca, one also
needs progenitor systems that undergo ignition at higher densities. We also
found that the total amount of $^{56}$Ni, the Si-Ca/Fe ratio, and the abundance
of elements like Mn and Cr (incomplete Si-burning ashes), depend on the density
of the deflagration-detonation transition in delayed detonations. Our
nucleosynthesis results favor transition densities slightly below 2.2$\times
10^7$ g cm$^{-3}$.
