Docboz

This is simply not true, FI is affected by altitude just not nearly as much. There's less oxygen at alltitude which requires the FI unit to work harder to make the same boost levels. This has been proven on many dynos.

miniceptor86

Could you help me understand about the Fuel Injection system "working harder" to make boost at altitude?

maplelakeduckslayer

Cause he means forced induction by saying fi

QwkTrip

Turbocharged engines do lose power at altitude. There is a 5 psi difference of air pressure between seal level and 10K feet. Asking the turbo to make up that difference doesn't come free. The intake air charge will have different temperature and pressure.

Docboz

Docboz

If you want i could point you in the direction of common acronym's for automotive use tho. I understand how using the term FI may confuse you but when its used in a sentence talking about boost its pretty self explanatory especially in a disscussion talking about NA vs FI (thats naturally aspirated vs forced induction).

miniceptor86

Well thanks then. Sorry I didn't make the connection. Earlier in the thread there was talk about the fuel injection system compensating for altitude.

Docboz

Ok sorry for the sarcastic response, i thought you were being sarcastic yourself.

miniceptor86

No sarcasm, just old brain not following.

Depending on what method of forced induction is being used the compressing mechanism may or may not be working harder. Any forced induction mechanism that is driven directly off the engine such as off the crank shaft such as positive displacement roots type or centrifugal pump would experience less resistance because of the thinner air at higher altitudes. Being governed by crank speed they are not able to compensate for loss of atmospheric pressure (density) and so suffer from "altitude sickness" similar to engines using atmospheric pressure to fill the cylinders.

The turbo charger because of the thinner air and no direct mechanical connection to the crankshaft will work harder. It is able to spin faster at higher altitudes than at sea level and thus maintain better induction pressures at altitude.

Kenferg1

Agreed. I just read some postings about WWII aircraft turbo and supercharging. Interesting setups in the old slide-rule days. The general consensus is that turbos provided better pressure, and therefore more power at higher altitudes. Superchargers were single or two stage types often being fed air by one or two turbochargers. The bottom line was max power at altitude for piston driven engines. While I have no evidence in the way of dyno runs at altitude vs sea level, I am sure that given the ability to manipulate boost pressures via tuning, increase fueling, and manipulating boost pressures, turbocharging has an advantage (however slight at 11-12,000 feet) to claim superiority. Now, set it up like the old timers did with sequential boosting into a supercharger... well that's a whole 'nother beast!