  The failure of purely gravitational models of X-ray cluster formation to
reproduce basic observed properties of the local cluster population suggests
the need for one or more additional physical processes operating on the
intracluster medium (ICM). We present results from 84 moderate resolution gas
dynamic simulations designed to systematically investigate the effects of
preheating - an initially elevated ICM adiabat - on the resultant, local X-ray
size-temperature, luminosity-temperature and ICM mass-temperature relations.
Seven sets of twelve simulations are performed for a LambdaCDM cosmology, each
set characterized by a different initial entropy level S_i. The slopes of the
observable relations steepen monotonically as S_i is increased. Observed slopes
for all three relations are reproduced by models with S_i: 55-150 keV cm^2,
levels that compare favorably to empirical determinations of core ICM entropy
by Lloyd-Davies, Ponman & Cannon. The redshift evolution for the case of a
locally successful model with S_i = 106 keV cm^2 is presented. At temperatures
kT > 3 keV, little or no evolution in physical isophotal sizes or bolometric
luminosities is expected to z < 1. The ICM mass at fixed T is lower at higher z
as expected in the canonical evolution model. ICM mass fractions show a mild T
dependence. Clusters with T > 3 keV contain ICM mass fractions depressed by
modest amounts (< 25%) below the cosmic mean baryon fraction Omega_b/Omega_m;
hot clusters subject to preheating remain good tracers of the cosmic mix of
clustered mass components.
