[Dominik]

Yes, DIN and SAE came closer in the early 70s. But the typical hot rodder likes the "old" SAE. Now, let me get into this:

A rear wheel horsepower reading of 500Hp does not translate into:
500x1,2 (20% drivetrain loss) = 600Hp, plus 80Hp exhaust and accesory loss = 680Hp. Let make it 700...

It does translate into 550Hp DIN (in my car, most cars).

Sorry, to burst your bubble: There is no 20% drivetrain loss (in direct drive, 4th gear).
Just imagine 100Hp which is about 70 kiloWatt (240000Btu) which would be the same as 70 off 1.000Watt electrical heaters, or blow dryers.

Your transmission would almost be glowing red hot.