The general consensus among most major tuners I've found is that a Mustang dyno is the one they prefer since it doesn't tend to overreport like others do.
I've had many vehicles on the dyno. It is not uncommon whatsoever to see differences sometimes up to 10 HP or more on the same day, back-to-back. Again, there are so many variables to consider for why this is. The bottom line though is that if an advertiser says their intake provides a 5-10 HP gain, they are saying that for a reason. Because they know damn well that you can't measure that sort of a gain with any sort of realistic results.
It helps to understand from the get go that while some vehicles suffer from restricted air intakes, the TJ is simply not one of them.
It's also helpful to understand that if you want more air into your engine that can equate to more power. However, it needs to be done in conjunction with a bigger intake, ported plenum, ported heads, tuning, etc.
An engine is a gigantic air pump. Simply opening up the air box a little will do absolutely nothing in most cases. Same thing as putting on a bigger throttle body. Why? That doesn't change the fact that the rest of the air intake path is still corked off.
