Is it true... (LT1 vs LS1)
Would this still be true if the heads and cam were changed in the LT1, as opposed to stock heads and cam. Ex: 400 rwhp LT1 vs. 400 rwhp LS1. I know torque would be another variable.

As was said, there are FAR too many factors to make a statement like that. Driver, gearing, auto or manual, stall, curve (one of the most important factors), etc.

