Originally Posted By: BikeWhisperer
Originally Posted By: Cujet
Originally Posted By: dave1251
Why? Less dense air means less air being squeezed in the cylinders=less power and heat. Less heat means a lower octane requirement because ignition detonation is less. So lower elevation locations require more octane and higher elevations require less.
Many of today's cars are turbocharged or supercharged. Altitude plays no role in turbocharged automotive engine performance. The lower octane negatively affects boosted engines. In fact, some cars require 93 octane, with good reason.
In theory a forced induction engine would not lose power at altitude with the turbo/super charger compensating for the lower density. However in reality, in order to accomplish this the turbine would need to spin at a greater rpm to suck in enough air to compensate for the lower density. This will result in you needing to run higher engine rpm's to attain the power resulting in a greater lag before the power comes on. In addition, higher engine and turbine rpm's means increased engine temperatures above the designed efficiency range and increased temperatures means decreased power. Finally the CAC will not cool intake air as efficiently because the lower density air will not provide as much cooling at 6000 feet as it would at sea level.
So while they will see less power loss than a normally aspirated engine, they will still lose power.
I understand your point clearly, as we've performed hundreds of turbocharged dyno runs and operational tests in Colorado.
For automotive use, and at typical elevations, my point stands. The normally aspirated 3% per 1000 foot lapse rate is easily offset by the turbocharger. The bottom line is that the turbine has to do slightly more work. What many people fail to understand is that there is sufficient waste energy in the exhaust gasses to provide this slight increase in additional work.
This does not result in significant HP loss at any normal elevation with modern cars. In fact, most automotive engines will produce rated power to high altitudes. In fact, Ford clearly states that the 3.5L produces peak torque to altitudes well above 5000 feet. Owners notice no difference in performance to 11,000 feet. The only real difference is the turbocharger(s) RPM.
As for intercooler efficiency and effectiveness, as a general rule, higher elevations are cooler. Intake air temperature is affected by overall system efficiency. Once again, it's typical to see normal IAT's at altitude in Ford engines.
Back to the question at hand. High elevation locations often sell lower octane fuels. In modern turbocharged engines, this can result in loss of power. Using 85 octane in a Ford Ecoboost is not within the specifications and not a good idea.