[vin63]

Originally Posted by theastronaut

..Instead of the forces being absorbed by the frame (twisting), the frame will be more solid and transfer the forces into the suspension instead. Boxing the frame should spread out the forces being transferred through the frame over a larger area. I would think that the engine/trans/body mounts would be less stressed since the frame won't be twisting as much; the mounts wouldn't see as much movement....

This is the same principle that allows the use of solid trans and motor mounts in full-chassis drag cars. As an example, when I raced my '63 Chevy II in bracket classes with only subframe connectors many, many years ago, I would occasionally crack my trans case. I built a full chassis with a 14-pt roll cage, solidly mounted my trans and engine with more than twice the horsepower, and have yet to crack a trans case in 20 years of Super Gas racing. These days, I build double frame rail chassises for really high HP applications, like my funny car where everything is solidly mounted to the frame.