I think recent Camaro owners had a similar thing happen, where the 1999 Camaro with it’s best engine option (forgive me, I cannot recall the lettering) was actually putting out near the same power as the Corvette. The Mustang message boards I used to hang around posted many dyno printouts stating as much, done on stock Camaros and Corvettes (why on the Mustang site? Beats me…)
Yes, I am referring not only to the claims of individuals, but also the spreading of these claims through inaccurate reporting, much like urban legends are spread.
Yes, I have particular experience with this engine. It’s funny though - every single person I meet with a 454 somehow happens to have the highest powered version ever made (how’d that happen? 
) - when there were actually very limited runs of these very high power engines, as I posted.
One article that comes to mind (sadly, unavailable to me now) compared all of the top-engined Mustangs of the glory years with a 1999 GT. All the way up to and including a 429 CID equipped one (I don’t think it was stock). The results were just plain sad. The 1999 GT had a peak power of 245 hp - none of these other Mustangs from the past got any closer than 230 hp, IIRC. The most sad one was a 351 that was “factory rated” at 390 hp, that achieved around 170.
I personally would consider 50 hp in that case to be an enormous difference, but that’s me.
Well, yes and no. One thing I am very careful not to claim is that the muscle cars of old were not fast. They were fast - very fast, even with poorer tires and without the proper suspension to put the power to the ground. My issue is that people treat cubic inches too often like they use pubic inches* - they always claim to have more power than reality.
Another thing that comes into play (that you already mentioned) is the quality of the power. The fat, broad, smooth torque bands of the larger displacement muscle car engines is wonderful, and yields a much faster car than is apparent by comparing peak horsepower numbers. This is why a 225 hp 4-cylinder NA 2.0 l car will not match up very well to my 225 hp 8-cylinder NA 4.6 l Mustang (you knew that, of course, I’m just trying to generally illustrate my point).
[sub]And because someone has to say it…for some women, there’s no substitute for pubic inches…[/sub]
Several things come to mind…
In the mid sixties and up, when the Musclecars were king and the insurance agencies weren’t quite up to speed yet- so to speak- engines were typically rated at “gross” horsepower, though they didn’t call it that.
Gross simply meant the maximum power the engine could produce on a dyno, without the parasitic losses of alternators, waterpumps or fans, and typically with a more free-flowing dyno-stand intake and exhausts.
As the insurance companies started leaning on the manufacturers, they simply “adjusted” the numbers. That 455 Hurst/Olds? Sure, it may have actually put out about 425 hp at 3,500 rpm (as I recall) but the “official” output as measured at the pamphlet might have been “400 hp at 2,800 rpm.”
It’s a horsepower CURVE, see?
And yes, the stickers… hey, stickers are worth two tenths in the quarter, don’cha know. My brother has a '70 454 Chevelle… it’s actually a “marine duty” block, meaning the engine was never intended to be installed in a car… But Year One has a great supply of “LS-6 454” stickers for the valvecovers and air cleaner…
Even Anthracite wouldn’t be able to tell the difference unless she got under there and checked numbers… Heck, it could have started out as a smogger 396 with a two-barrel out of a '72 Caprice wagon. You think the owner is going to actually tell his buddies it’s “just” a 396?
Anyway, over the years, engines were rated differently, even by the same manufacturer. The HP as measured at the crankshaft with no accessories, will of course be greater than WITH the accessories. HP measured at the tranny output shaft will be lower still, and different between a manual and an automatic. HP measured at the rear wheel is of course lower still, but perhaps a little more applicable to the “real world”.