Banks experiment - altitude and hp
Neat video...I skipped past some of the explanation portion as it drug on some. His 8.1L starts out at 347hp and then drops to 285hp at 5600'. Video
Forum Discussion
valhalla360 wrote:
- 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 mentioned, many vehicles run superchargers.
No, I didn't assume superchargers run wide open. They're throttled just like NA and turbo gas engines. But regardless of how much you open the throttle, they have a fixed pressure ratio (boost ratio).
If the ratio is 2:1, at sea level, 100% throttle, then you manifold pressure is 14.7 psi. At an elevation of 0.8 atmosphere, you'll be at 11.76 psi.
At 50% throttle, you'll be at 7.35 psi, and high elevation 5.88 psi (grossly simplified, but you get my point).
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).
With NA, I bet test results = math.
To guess a turbo's "room" left to boost at altitude, you could look at how much top end hp a vehicle gains with only a tune.
On small turbo engines like my lil Mini Cooper, a tune can gain 30% of torque in the mid range, and only 10% above 5000 rpm. We can make an educated guess at say beyond 3000 feet (0.9 atm), it'll probably start to lose power. Because at that altitude, it requires the turbo to generate 10% more boost ratio.
