This Astronautix page gives the old Saturn F-1 engine a vacuum thrust
of 1,740,134 lbf at a weight of only 18,498 lb for a thrust to weight
ratio of nearly 100 to 1:

F-1.
http://www.astronautix.com/engines/f1.htm

The Astronautix page on the Ares I solids give it vacuum thrust of
3,480,122 lbf but an empty weight of 221,230 lb (!) for a thrust to
weight ratio of only 16 to 1 (!):

Ares.
http://www.astronautix.com/lvs/ares.htm

The tank mass for a kerosene-LOX engine is only about 1/100th that of
the propellant mass. So even if you used the same propellant mass as
the Ares I solids of about 1,400,000 lb that would only add 14,000 lb
to the lower stage empty mass. But actually the propellant mass would
probably be less since the F-1 had a better Isp at 304 s compared to
265 s for the Ares I solids.
Given this, how much larger payload could we launch to LEO using the 2
F-1 engines in place of the Ares I solids as the 1st stage?
How much could we launch to LEO using just 1 F-1 engine as the 1st
stage?


Bob Clark