Originally posted by: SVT Cobra
Originally posted by: Heisenberg
Originally posted by: Whoozyerdaddy
Originally posted by: Heisenberg
Higher altitude = lower pressure = less oxygen per unit volume to combust.
That's what I figured but pleanty of other cars seem to make it up to the top. (10,023') Wasn't sure why mine would crap out.
I dunno. You could have a slight problem in something like an O2 sensor that's not an issue at lower elevations, but keeps the PCM from getting the air/fuel mixture right as you go higher.
Edit: Oh the thing is supercharged? That's really odd - a supercharger helps a lot with power loss at altitude.
Let?s start by noting air is the working medium of internal combustion engines, and the more air (mass of air) processed by the engine, the more power it will make. We also all know air density decreases with elevation, so engines lose power the higher they operate.
Let?s also note supercharged and turbocharged engines are naturally aspirated upstream of the supercharger or turbo. In other words, we?re still relying on something (atmospheric pressure) to drive the air into the blower or turbo. So, the higher we go, the less power the engine makes unless something changes to process more air through the engine. As you noted, the naturally aspirated engine loses power because it can?t process any more air?the engine can?t magically grow displacement or increase rpm. Likewise, a mechanically driven supercharged engine doesn?t get any larger, doesn?t rev any higher nor does the supercharger turn any faster. Therefore, the mechanically supercharged engine doesn?t process any more air and begins losing power as it rises above sea level just as a naturally aspirated engine does. This effect is typically masked in automobiles because the supercharged engines have so much power at sea level that it?s easy to use full throttle earlier and longer while driving in the mountains and not notice the difference. The same is true of turbocharged engines, except for one thing. Turbocharged automotive engines are often fitted with relatively large turbos with excess capacity at sea level, plus a wastegate to limit turbo boost. Take such a car into the hills and the wastegate simply stays closed earlier and longer, and voilà, a sea-level air mass is forced into the engine. Well, it is until the engine?s critical elevation is reached; that?s where the turbo system runs out of capacity due to its sizing, or insufficient atmospheric pressure to feed it, and then only sea level or less power is possible. The important point is a forced-induction system has to increase speed or have reserve capacity to maintain sea-level horsepower at altitude. This can be done with a mechanically driven supercharger if fitted with a transmission (once common on aircraft), or as we saw, more easily with a turbo. Likewise, some turbo systems are carefully sized to limit sea-level boost to a predetermined level and have no wastegate. Such engines cannot spin the turbo faster or earlier, and they lose power with elevation starting immediately. But again, they likely have so much power to start with, you can use more throttle earlier and not notice any drop for the first 2000 to 3000 feet of elevation.