Banks experiment - altitude and hp

RoyJ wrote:

valhalla360 wrote:
It would be fun to see a series of similar tests with diesel and turbo vs non-turbo.

As you say it matches the math but it's always nice to see confirmation.

A naturally aspirated diesel would have the same ratio of loss as an NA gasoline. A supercharged engine, despite popular belief, also loses just as much power with elevation gain as NA, as the supercharger is spinning at a fixed rpm. Unless the supercharger is purposely bleeding off boost at sea level, and then doing full boost at elevation.

With turbos, it depends on the size of the compressor. If they're undersized, like say an Ecoboost (for throttle response), then at high elevations you'll run into the limit of the compressor, and lose some power. Usually significantly less than NA though.

With a "performance" turbo, where the compressor has plenty of room left on the compressor map, then at elevation it may retain near 100% of power. Trade-off is a relatively laggy throttle response.

Exactly. I'm not sure everyone realizes turbodiesels do well at altitude because of the turbo, not because they are diesels. Gas turbos reap the same benefits.

Interesting fact regarding superchargers and altitude. Some supercharged airplanes had two speed superchargers so they could spin the supercharger faster at high altitudes to gain some power back.