GM advertised horsepower jokes
 

Don't bet the pink slip on GM advertised horsepower claims. I've never heard of any C5 vet dyno stock higher than 295 RWHP! If my math is correct that would not equal 350 horsepower. I think that would be 295 RWHP and 335 HP. Try a Ford SVT 2003-2004 Cobra that honest Ford claimed at 390 HP except I own one and have several fellow owners that had the same baseline HP experience. 03-04 Cobras dyno at 401-405 HP at the flywheel (more not less than advertised horsepower numbers) thats 342 RWHP! By the way for about $5400 worth of bolt-on parts and top race team labor rates (Johnny Lightning Performance) a cobra will put over 600 true RWHP. By the way, try looking up a 2001 corvette recall and service bulletin on edmunds.com and see the 28 page list, then try looking up a 2003 SVT Cobra and find 0 recalls and 0 service bulletins. I have owned several high performance vehicles over the years and have a small collection now. I like the C5 vette, Love the 03 Cobra.

RE: GM advertised horsepower jokes
 

Well I've been to many "Dyno Days" and I never saw a stock Corvette C5 dyno any less than 295 RWHP. In fact, my 01 dynoed at 316 RWHP with no mods. After just an intake and exhaust, it went up to 329 RWHP. Divide that by .88 (12% drivetrain loss) and I've got about 375 HP. Add a $6000 ATI supercharger and I'm looking at 525 HP. Couple that with a vehicle that weighs in at 3200 lbs and you end up with a modded Cobra-squasher in acceleration AND handling. It's great that the Cobra has the dyno numbers, but that cast iron block and steel body really does a number on it at the dragstrip.

RE: GM advertised horsepower jokes
 

Well the one thing you have to realize with the whole HP issue is that Ford actually underrated the Cobra. For what reason I couldn't tell you, but it probably had to do with insurance cost for potential owners. Based on what a C5 will dyno at the wheels GM is pretty much dead on with the crank HP ratings.

RE: GM advertised horsepower jokes
 

Add a blower to the Vette and the Cobra gets eaten alive. GM actually rates their HP pretty close to what is advertised, Ford has generally done pretty well there also. Chrysler corp. has generally been a bit high in their claims excepting the Viper.

RE: GM advertised horsepower jokes
 

There will always be some controversy about how to compute equivalent HP ratings from rear wheel dyno tests. What I would ask Snake Bite, is that we have no bashing of any type here: you original note is close to that: vettes don't put out power but my car does . . . nah nah nah, come on -- that's immature and isn't what any of us like to see on any forum. Vettes are good cars, so for that matter are Mustangs, whether Cobras or just plain GTs -- even V6s are pretty nice, actually. Every car enthusaist loves their particular car, even if it is a Trabant, so just leave it at that . . .

As for RW HP the most widely used rule for conversion (but maybe not the most accurate) is 15% losses from the flywheel. Which means that 295 at the rear wheels corresponds to about 340 HP. But most stock C5s (A4) I have seen do about 292 on a rear wheel dyno - always within a 10 HP band around that figure, and m6s I saw would do around 295 to nearly 305 - the average is about 300 (before retuning) which is the # I use (I know some owners claim the average is 305 but I haven't seen it, and of course most people who own Fords claim C5s do "only" about 295. I have seen up to 315 on a stock M6 vette after careful re-tuning of the ECM to lean it out and advance ingition to the limit premium fuel will allow. That is stock.
Regardless, I use 300 for the M6 because it is what I have actually seen as they come from the factory.

What that corresponds to is up to how you compute it: I always assumed the factory is correct and the earlier ones were 345 HP, so 300/345ths means there are 13% losses. On the other hand, my ZO6, when stock put down a baseline stock best run of right under 360 (359.8) and 360/405ths==>11% losses). That is the figure I inverted to estimate flywheel HP for all my mods: 640 rwhp x (405/360)=720 flywheel, etc.

Some cars were underrated by the factory: One was the LS1 Camaro. My Camaro (305 Hp rating) put down 288 when stock (5.5%) losses from 305 HP, but of course it was well understood that GM fudged the #s down slightly to give the 'vette more HP advantage at the brochure, and this number indicates it was somewhere around 325-330 at the usual 11% losses for the GM M6 drivetrain I use. Another underrated car was the '03 Cobra: why Ford underrated it, I don't know. I have not seen a stickly stock one put down 390 rear wheel HP, (stock with only a pulley change is another matter, of course) but I've seen two that did put down about 377 -380, which is close, so I always assumed they were about 425 Hp from the factory. It is worth noting that the Ford GT so puts down very close to its rating at the rear wheels, so maybe Ford just underrates its SC'd engines.

On the other hand Ford rates its other cars consistent with GM (and Chrysler for that matter): I've watched two dyno tests of '05 M5 Mustang GTs (300 HP rated, 260-265, which is around 14-12%. I saw a T-bird (280 Hp 4.2 liter V8) put down right at 245 with a manual trans, again, right at 13%. And yes, I know the factory does not put a manual in those cars, this guy had installed one from a Jag which of course was an easy fit since its basically the same engine, and later SC'd it which turned it into a decent car (300 rwhp).

Porsche is about the same way: my 320 Hp rated 996 puts down 265 (17% losses - automatic, and a similar car with the M6 put down 280 (13.5% losses).