It seems that we’re living in a new era of factory horsepower wars. Hot on the heels of the announcement that the forthcoming Camaro ZL1 will make 580 horsepower, we have some one-upsmanship from Ford with their news that the 2013 GT500 will have 650. While that might seem like the final shot fired in that particular Ford versus Chevy battle, I’d like to point out that not all horsepower numbers are created equal, and that the Blue Oval brigade should probably wait until those Mustangs are actually rolling off the production line before they claim victory. Here’s why:

As information about the ZL1 became public, it was clear that Chevy was playing a very conservative game with the information they were releasing. At first, even the name was shrouded in mystery, with most news outlets (including us) referring to the mystery top-of-the-line Camaro as the Z/28 before the true ZL1 designation was known. Then, photos of test mules appeared, placarded to indicate the engine being used was a derivative of the Cadillac CTS-V’s 556 horsepower LSA.

With that information, it became possible to take a reasonable guess at where the true horsepower output for the ZL1 would fall – we discovered that the ZL1’s number would be “north of 570 horsepower,” and it would also be reasonable to assume that Chevy wouldn’t build a Camaro with a better number than the ZR1 Corvette at 638, so we knew it would fall somewhere between those extremes.

Then, Chevy took the production-spec ZL1 engine in for SAE testing, which is a Big Deal: the rigorous protocol is the industry standard for advertised horsepower, and you can get in a lot of hot water for fudging this number (more on that in a minute.) Even with testing complete, we couldn’t pry the true number out of anyone inside Chevrolet, because they were concerned that a leak traced back to them would cost them their jobs.

Finally, we got the official announcement: 580 horsepower “at the brochure” for the ZL1, eclipsing the existing GT500’s 550.

Compare that to how the 2013 GT500’s horsepower number became public. In contrast to how close to the vest Chevy played the ZL1’s information, Ford was almost casual about it. “Oh, yah. 580 horsepower, that’s nice for you guys. The Shelby will have 650.” That’s certainly a nice round number, and it will mean that the GT500 outguns the mighty ZR1 Corvette. If it turns out to be true, of course.

You see, Ford has a history of playing fast and loose with Cobra horsepower numbers – ask anyone who bought a ’99 about that. While rated at 320 crank horsepower, those production cars suffered from intake, cylinder head/compression ratio, and exhaust restriction issues that Ford internally rated at a total deficit of between 13-15 horsepower, though debate raged among enthusiasts about what the real number was. 1999 SVT Cobras were recalled to remedy the defects, and production of a 2000 model was suspended to allow the problem to be corrected.

In the wake of that debacle, Ford introduced the supercharged 2003 Cobra, which turned out to be substantially underrated, the company having apparently learned a lesson about disappointing buyers of your top-of-the-line performance car with less horsepower than advertised.

So where does that leave us? We have Chevrolet, with the ZL1’s take-it-to-the-bank 580 SAE horsepower. And we have the 2013 GT500, with a promised 650 horsepower rating. Will it actually live up to that promise, like the ’03 Cobra did? Or will it turn out to be just a number pulled out of thin air to take the spotlight off of the Camaro and buy some time while Ford comes up with an actual, production-spec powerplant for 2013?