I bet you somewhere someone calculated exact drop in power. But for N/A engines rule of thumb is 3% of loss. Your butt dyno, depending on vehicle, might or might not notice difference (your cooling system on other hand will, for sure). For example, my 328 with some 270hp on crank and some 225-230lb-ft, it is still quick, it is quick at 10,000ft. But it is 3600lbs, stick shift. My 2009 Pilot? Oh boy. That is slug fest once you cross 8,000ft which is pretty much anywhere in CO once you hit mountains. Sequoia with 5.7? I can feel it, but there is enough power to still leisurely push it.
Now, Tiguan doesn’t struggle whatsoever. Only thing I can feel on “butt dyno” is bit longer turbo lag. My Atlas was similar and proven far more powerful at 11,000ft than Atlas with 3.6 VR6 and less weight. 2.0T had 235hp and 258lb-ft, 3.6 VR6 is rated 276hp and 266lb-ft at sea level. At 11,000ft? I obliterated VR6 with roof box, three bikes on bike rack and full trunk of bags, grill, cooler etc.
Now, how much pressure turbo makes compared to sea level at 14.7psi atmospheric pressure? Don’t know. But, unless vehicle has really good power to weight ratio like my BMW (and they are known to have much lower losses through drivetrain) turbo is way to go at altitude.
6,000ft? It is still ok. My house is at 6,800ft. But, once you hit mountains, 6-8-% grade, 8-12,000ft (in some cases) it becomes struggle. Not to mention that at that attitude cooling engine is far less efficient than at any ambient temperature, regardless how high, and now you are 30-35% down on power, pushing high rpms to go over pass, and cooling system is now working overtime. Turbo? You can do all that, but between 2-3,500rs, instead 5-6,500rpms.
