This is an old "gentleman's agreement" to keep each manufacturer from one-upping the other by adding just a few hp. I think it was a great idea, and certainly much better than the myriad of American lies, which include but aren't limited to...
- presenting hp as "gross", meaning without smog pumps or other power-sapping bits (re: muscle-cars)
- deliberately underrating the hp by quoting it at non-peak rpm (re: L88 Corvette)
- waiting until the last minute to release your hp stats so you could have 10 more than the competition (re: all of them), or...
You get the picture.
"Gross" horsepower wasn't a lie. It was an outdated testing method that stuck around since the Model T (when cars really didn't have any accessories to drive), but it wasn't a "lie." The methodology was published (in fact, it was an SAE standard, specifically, J245 and J1995) and could easily be replicated. Since every US car used that methodology at the time, it also allowed intelligent comparison among different US cars. It's confusing to us now because we're accustomed to SAE "net" horsepower (SAE J1349) as the ratings method and comparisons between "net" and "gross" ratings are difficult. But at the time the SAE gross standard was used it was absolutely an independent standard. I suppose that you can say that they should have switched to the newer J1349 standard sooner, but it was hard enough to explain the different method to consumers when every car company switched at the same time. Can you imagine trying to be the one company that switched when the others didn't? There's no way you'd be able to explain to the average consumer what the difference was.
How is deliberately underrating the L88 any different than deliberately rating an engine at "276 hp" even though it put out over 300, which is what the Japanese were doing? At least with the L88 it was underrated to intentionally discourage non-professionals from buying the engine. Hell, the L88 didn't even have a heater or a choke on the carburetor in the first couple of years. At least the underrating of the L88 (and other "super" engines like Ford's 427 and 428 engines) was due to lower redlines for the street versions (which were warrantied) than on the race versions (which were decidedly not warrantied). The Japanese 276 hp "gentleman's agreement" only happened because the manufacturers were afraid that the government was going to step in and legislate the maximum power. The Japanese manufacturers agreed not to advertize more than 276 horsepower and the government agreed to back off from its push to create a horsepower limit that was imposed by law.
I'll grant that waiting until the last minute to release specs in order to preserve a bit of one-upsmanship is annoying, but it's not really a "lie" either. As long as the stats are accurate it's just annoying marketing. It should be noted also that back around 2005/2006, Honda and Toyota were found to be over-stating the horsepower in most of their cars. For example, the 2005 Camry V6 was rated at 210 hp, but, after re-testing, the exact same engine in 2006 was rated at 190 hp.
All of this is not to rag on Japanese manufacturers, but rather simply to point out that your disdain for US manufacturers is misplaced. The issues surrounding horsepower ratings are present for all manufacturers and there really aren't any that are particularly worse than others.
