Stop in for a cup of coffee

It's because you aren't using the equation correctly. To determine HP you need to know the torque at a given RPM and then apply the equation to get the HP at that RPM.

Torque at any given rpm does not meant that you can use the equation to calculate the entire torque range unless it is a completely flat or linear curve and you already know what the slope is. The short answer is that the equation is only used to calculate one value from the other (HP or Tq) at any given RPM, not across a range
OK.. i get that on a chassis dyno there are torque multiplication factors from gearing and parasitic losses...... I'm just looking at engine dyno stuff (which seem to use about 3k as their bottom rpm range). But if any engine makes 300 lb-ft of torque at 2626 rpm, horsepower is half that? Math says so... and if it makes 400 T, HP is 200???? Just trying to wrap my head around it. Seems the 'gap' between HP and torque curves should look the same (or similar) for any engine (granted it's torque producing properties could make the slopes of the lines radically different, but the numeric 'gap' should remain the same, percentagewise).. i may be high tho...