I didn’t know most of this and I just thought it had to do with emissions, etc. It’s a really interesting read, too much to quote:
There are a lot of misunderstandings among car enthusiasts and historians about vintage horsepower ratings… When asked the reason for the huge difference, gearheads tend to shake their heads and mutter about emissions controls and anemic, low-octane unleaded gasoline — which is true, but only partly.
The 2005 changes “SAE Certified Power” includes fully dressed engines with full application specific exhaust systems, so you truly get a accurate representation of engine output. A 500hp engine of the 60’s is nothing like a 500hp engine of the 2000’s. Most Ol’ timers are unaware of this.
When it comes to manufacturers underrating their HP figures, as far as I know BMW HP ratings are close to actual WHP! I could be very wrong though…
Manufactures still don’t report accurately. Cars are getting so powerful on the performance side of the model line that to me the numbers don’t really mean anything anymore to me when comparing stock to stock.
I do always find it interesting to talk with older “muscle car guys” that get on talking about how fast their cars were back in the day when the reality is that most muscle cars suck from a daily driving stand point. Terrible torque curve, terrible reliability (if they were fast), high maint and so on