SIMPLEC (SIMPLE-consistent) is selected by setting "consistent" option true/yes:

SIMPLE
{
    nNonOrthogonalCorrectors 0;
    consistent yes;
}

which relaxes the pressure in a "consistent" manner and additional
relaxation of the pressure is not generally necessary.  In addition
convergence of the p-U system is better and reliable with less
aggressive relaxation of the momentum equation, e.g. for the motorbike
tutorial:

relaxationFactors
{
    equations
    {
        U               0.9;
        k               0.7;
        omega           0.7;
    }
}

The cost per iteration is marginally higher but the convergence rate is
better so the number of iterations can be reduced.

The SIMPLEC algorithm also provides benefit for cases with large
body-forces, e.g. SRF, see tutorials/incompressible/SRFSimpleFoam/mixer
and feature request http://www.openfoam.org/mantisbt/view.php?id=1714