One has to take all mfg hp and torque claims with a grain of salt.
That said, a well-designed DP will eliminate the severe restriction in the neck of the stock DP design, and is likely to have a full 3 inch internal tube diameter. It will either be catless or have a high flow cat, since the original pre-cat in the DP is pretty restrictive. It will be followed by a race pipe (RP that is catless, or the RP will also have a high flow cat. You probably already know all of this.
Most of the DP/RP combos out there from reputable manufacturers have high quality build and meet these basic design needs. So, most are going to perform in a very similar manner, just like most aftermarket SRI's or CAI's will perform similarly.
My point is that you should probably not dwell on whether Cobb's claimed numbers, if any, are accurate. They will be very close to that of any other DP from anyone else, if you are comparing catted to catted or catless to catless.
What is the big deal is that a good DP/RP regardless of the manufacturer, if it is a good product and fits well, is going to produce a huge bang for the buck in increased performance, especially if matched with a good aftermarket intake.
Actual dyno numbers are going to vary from car to car depending on other mods, depending on the model of dyno, depending on where the dyno is located and depending on temperature, humidity and literally a thousand other variables. You can see pretty significant differences in dyno numbers from the same dyno on the same car on different days.
Regardless of the hp and torque numbers (I've got them, but it is pretty meaningless for comparisons to other cars), a simple measure of performance gain can be done with a cheap stop watch by measuring times from 30 mph to 100 mph on the same road surface before and after mods, or by using an accelerometer for the same purpose, but measuring from the moment of launch. The numbers you get apply only to your car, but are highly repeatable.
With my performance mods, which are pretty much a true CAI and a catless DP/RP, and colder plugs, my times have plummeted.
Look at the attached graphic from an accelerometer run a couple weeks ago, time v. speed Even with the really crappy launch, the power, once the car hooked up is amazing.
Then run, do not stop, but run to some vendor of your choice and get a good DP/RP and a set of one step colder plugs. If you don't have a good SRI or CAI, get one at the same time. You'll be very happy you did this. This engine is already running pig rich, so the stock ECU will still be able to keep everything within safe parameters for these mods.
