Builder had another engine that might be more suited to sonic games. I forgot where it is though.
I think what you're thinking of was more of a proof-of-concept that the sonicTI developers at UTI were doing it all wrong, thinking about advanced physics when in reality it was much simpler -- apparently Builderboy's engine wasn't optimized enough or even written in a dynamic way to support a full Sonic game, as he said. However, if anyone is making a sonic game I sincerely bade you to search for his sonic engine, it was very well done overall.
