I'm no engineer, but, being around streamliners and engineers awhile, I would say that you would need around 2500-3000hp (reliable hp) to achieve these speeds in the 400-450 range. Summers Bros. was around 2400hp. Where's Pork Pie?? The 411s setup was, if I remember right, about 2350hp each at 7500rpm. So 4700hp not withstanding drivetrain power loss to the wheels, and if everything is working just right. I think the idea on multiple engine cars is to have enough available hp to not over stress the engine package.