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It helps not to work in ridiculous units. Power = torque x angular velocity

So in this case let's take the position of the bend, where power goes flat (4000rpm, 250kW, 600Nm): P=4000 x 2x pi/60 1/s x 600 Nm = 251kW

Seems to be correct.

The scales are different: torque is from 0 to 700 Nm, power is from 0 to 300 KW.

I didn't see any graphs in units of hp or ft-lbs. Do you have a link?

There's a torque-to-kilowatt graph roughly near the top of the article, and you can convert kw to hp by multiplying by 1.341.

Crap, my bad, I didn't even realize the graph was using NM and kW. I'll go back into my cave now.

> HP & Torque curves vs RPM should always cross at 5252 RPM

Not really. First, this number only applies to imperial units. Second, axis scaling will move the crossing point. The only way this happens (provided we are talking about imperial units) is if the torque and power axis scales are explicitly scales such that the curves intersect at 5252 RPM.

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That doesn't appear to be true? https://auto.howstuffworks.com/question622.htm Mathematically, the OP seems to be correct.

It is mathematically impossible for the curves not to cross at 5252.