effects of elevation
 

As i understand it naturally aspirated engines lose approximately 3% per 1000 feet. So instead of ~170whp stock i am closer to 150whp at 4500 ft.

The question I have is does anyone know how this affects mods and tuning. Meaning will i get lets say 25hp from hks headers or will it also be dropped by that amount.

Will it be linear or will i get more/less at elevation than people at sea level.

An experienced tuner could answer this more accurately than I can. Since the air pressure is a measurement of available air density, the amount of air your engine can ingest is limited. The only way to overcome this limitation is via forced induction (turbo or supercharger). You need more air density to make more power, no matter the tune. So mod for mod, a car tuned at altitude will always make less power than a car at seal level because there's fewer air molecules to mix with the fuel.

The fuel contains the energy to make power, but it's ratio to the air molecules needs to be measured precisely. So, less air means less fuel, which ultimately means less power.

This is also why higher elevations may only see 91 octane gas instead of 93. We have fewer air molecules to compress, so less heat is generated before combustion, and there's inherently less risk of preignition (detonation, knock, ping) making lower octane safe.