I may be wrong here but this is what I think. GM didn't develop the 400sb as a performance engine because when this engine was introduced the performance era was over. This motor was developed to be used in trucks as a torque motor. The extra displacement was used to compensate for the effects that the emissions systems of that era had on power. GM would be remiss in developing this engine as performance motor as there was no market for a performance motor at that time and it would be money wasted. This scenario seem logical to me. It took a while before the performance aftermarket took notice of this engine and began to understand it. That is why performance development has bee lagging. Correct me if I'm wrong please but that is the way I see it happening.