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.

As I said, I understand the math but it's always nice to see how it turns out in reality.
- I don't think any production vehicles are running superchargers...so not really relevant but even there, you are assume they are on 100% of the time. Assuming there is a control mechanism, there can be a difference.
- As you indicated, the turbo may run out of blow at some point, so how close to the theoretical no impact does it get?

My intent was actually 4 options:
- NA gas
- turbo gas (production style turbo)
- NA diesel
- turbo diesel

Theoretically both NA should see similar percent reductions and both turbo should see similar percent reductions but actual field tests can bring to light issues not readily apparent (like small turbos only partially negating the thin air).