The new SLS (Space Launch System) booster will be slightly larger than Sat V. It's beyond planning and into component testing now.
There's a cool article on the net about the efforts to reverse engineer the F-1 first stage engine to build a new F-1 for the SLS strap-on boosters. The Sat V engines were built by welders and other skilled craftsmen; even the holes in the mixing plate in the combustion chamber were drilled by a guy at a drill press -- they could see his drill placement mistakes.
Oops — that’s the article I was thinking of.
The SLS relies on extended versions of the SRBs from the STS. That was F U N. Anyway, 3.5 million pounds of thrust is less than half a Saturn V, but engine for engine is bigger than an F1. The liquid fueled engines being built for the SLS won’t get the contraption off the ground — they’d be better off dumping the big useless liquid fueled mains and using all SRBs, with cryo-fueled upper stages for the trip out of Earth orbit.
http://www.freerepublic.com/focus/news/3266795/posts