Exactly. The bigger the mismatch then the bigger the gain. I've seen over 100 hp difference before by changing the intake manifold so 100 hp on the exhaust side is within reason. Or you can flip the script and design an engine that would have basically zero difference between HP manifolds and headers. People who just look at the two numbers don't understand what is really going on.
What real world engine would show zero difference between HP manifolds and headers?
Excellent question even if it is rhetorical.
Rhetorical answer time, a non-running engine or one running so poorly as to be non-functional.
For those wearing blinders the point of discussion is that without knowing what cam and without tuning for the application this dyno is about as useful as a square of used TP. Do headers help? Most of the time but they have their issues as well. They are noisier, they put more heat into the engine compartment when running, they can have fitment issues, they are more prone to leaking, many hang real low and get damaged, finally they can make other maintenance chores more difficult. Cost is also a factor as the ones that have less of the issues mentioned are likely to be the more expensive ones as well, Quality costs.
If your only concern is HP then headers are part of the plan. If the issues I mentioned concern you then headers may not be part of the plan. Also, the more mild the combo the less help headers are and the more likely the issues headers have are important.
