Track times really tell the tale. Dynos can be manipulated way to easy.
For example, let the car completely cool and make a run. Then make 3-5 more back to back runs and the power will start to decline due to heat soak. What's to say the base line wasn't a dead hot run and the new and improved a bone cold run? A true 5HP gain now becomes 11-15 on paper.
Dynos are really nothing more than tuning tools. The times I've tested parts, I've done it back to back without ever unstrapping the car from the dyno. Same tire pressure, etc. I do three runs and take the average. That will give the best idea of what it actually gained. You also have to watch the correction factor and smoothing used as those can both affect the numbers.
Here's the testing I did on the Challenger with cat back and CAI.
<table border="1" cellpadding="3" cellspacing="5" width="498" align="center"><tbody><tr><td width="120">
Stock Intake HP
</td> <td width="120">
Stock Intake Torque
</td> <td width="120">
Mopar CAI HP
</td> <td width="120">
Mopar CAI Torque
</td> </tr> <tr> <td>
Run 1: 335.08
</td> <td>
355.52
</td> <td>
340.19
</td> <td>
366.86
</td> </tr> <tr> <td>
Run 2: 333.97
</td> <td>
356.11
</td> <td>
340.14
</td> <td>
358.89
</td> </tr> <tr> <td>
Run 3: 335.77
</td> <td>
358.98
</td> <td>
340.73
</td> <td>
364.32
</td> </tr> <tr> <td>
Average: 334.94
</td> <td>
356.87
</td> <td>
340.35
</td> <td>
363.35
</td> </tr> </tbody></table>
<table border="1" cellpadding="3" cellspacing="5" width="600" align="center"><tbody><tr><td>
Magnaflow 16515 HP
</td> <td>
Magnaflow 16515 Torque
</td> <td width="120">
Magnaflow 16515
and
Mopar CAI HP
</td> <td width="120">
Magnaflow 16515 and
Mopar CAI Torque
</td> </tr> <tr> <td>
Run 1: 347.01
</td> <td>
373.36
</td> <td>
347.98
</td> <td>
373.02
</td> </tr> <tr> <td>
Run 2: 344.40
</td> <td>
370.07
</td> <td>
346.64
</td> <td>
373.70
</td> </tr> <tr> <td>
Run 3: 343.85
</td> <td>
365.20
</td> <td>
347.01
</td> <td>
368.26
</td> </tr> <tr> <td>
Average: 345.09
</td> <td>
369.54
</td> <td>
347.21
</td> <td>
371.66
</td> </tr> </tbody></table>
Now with the motor and blower it's right about 600RWHP and 600RWTQ.