Christos

I know we has a bit less O2 up here, but does this mean that since we are 2.X PSI less than sea level up here, that we can boost by another 2.X psi to 'fix' the altitude problem?

~RedLineLs1~

iTrader: (1)

www.bandimere.com

You will actually see better times at bandi even though its higher then PMI (in Pueblo). Bandimere is a very nice track...especially compared to PMI. But Im only 10 minutes away from PMI...so it doesnt bother me too much.

Tiago

iTrader: (27)

if the gauges are calibrated at sealevel, does that mean that if you are at 8000 ft and reach 10 psi , I would assume the turbo already made up for the losses from the altitude, or in otherwords, that would bein absolute pressure.

MIGHTYMOUSE

iTrader: (59)

thats what i'm thinking.. but

hey people in the upper atmosphere.. what do your guages reed with the engine off? is it in vaccum any or no?

RealQuick

iTrader: (14)

I never thought I'd see the day when a neon can smoke an fbody...

y2khawk

iTrader: (5)

One of the guy's i work with is heading to colorado over christmas vacation. I'm gonna make him take my old mechanical gauge as a test reads 0 here...

klatinn

Hi,

Just stumbled over this thread.
It's really very simple. Air mass per volume (density) is dependent on (absolute) pressure and temperature. If you would run the same ABSOLUTE manifold pressure with the same IAT, you would make the same power regardless of altitude. Typical boost gauges do not display ABSOLUTE pressure though, but relative pressure (gauge pressure), relative to atmospheric. So if you use gauge pressure, you make less power because you put less air MASS in the engine, even though the indicated boost level (relative to atmospheric) is the same.
I said above 'same IAT', because to make the same absolute pressure at altitude as at sea level, the turbo needs to work harder (faster). This raises IAT's. Hotter air has a lower density -> result is less power even for the same absolute pressure. As the outside air is also less dense at altitude, an intercooler works less efficiently as there is less air (mass) flowing around it to cool.
Lower air density at altitude also means less aerodynamic resistance at high speed. For some forms of racing this can offset the power losses a little.

Example:
Airplane engines very typically encounter power loss with altitude. This can cause problems during takeoff from a high level airport. The FAA does not allow aftermarket turbo kits to increase engine power beyond the sea-level rated power. BUT, they do allow a turbo kit that maintains sea-level (absolute) pressure in the intake, regardless of altitude. This kit allows the engine to maintain sea-level power rating at altitude.

Regards,
Klaus

red ws6 99

As stated most "boost" gauges (and most pressure gauges) will read zero at whatever atmospheric pressure they are located. Pressure transducers can be absolute type (most often) or gauge (atmospheric) compensated. Power is influenced by temperature, altitude, humidity,etc. So while a turbo will maintain a constant pressure ratio no matter what altitude you are at it will not maintain a constant density ratio. So you will have power fluctations. My car ET/mph will fluctuate the same as a normally aspirated car under the same weather variations. If temperature and humidity is up the normally aspirated cars (not just f-bodies) will go up a tenth and so will my car. The intercooler efficiency will also drop due to the density loss, plus the compressor will have to spin faster to make the same boost. Both lead to hotter intake temperatures.

Its not uncommon in southern New Mexico to have density altitudes in the summer time of 9000 ft even though actual altitude of 4200 ft, because air temperature is 100+ and humidity is 30+%.

Gary

Christos

So if you are living high up here like I am, does that mean that I can boost more, to match closer to what the sea level's, "absolute" pressue would be?

klatinn

Hi Christos,

Yes you could boost to the same absolute pressure (or higher gauge pressure), but you would need a bigger intercooler to compensate for the lower compressor and IC efficiency at altitude.

Regards,
Klaus

GrannySShifting

iTrader: (10)

I would run more compression

~RedLineLs1~

iTrader: (1)

Its not so fun...trust me.

eviltwins

So you're limited to being able to run even less boost at altitude to compensate? That doesn't make much sense.

Rudolph

iTrader: (1)

Damn, many of you complain about altitude, but where i live is every day´s bread. I live at 8500 ft, and i feel my car strong, but when any lower than that, i feel the car as a total beast.

You could say that every 100 meters is a 1% less of your engine performance, so lets put it this way, if you have 300 hp and you are at 1000 meters of altitude you get 30 hp less that would put you on the 270 hp range. The meters to feet conv. is 0.383 ft i think, so it would be every 383 ft you lose a 1% of your engine performance. The 1% rule may vary obviously depending on the air humidity (which engines love), the temperature, that is base on a 16°C as excellent (every extra 5°C is a 1% less, due to the heat), mmm! sorry, but i do not remember the factor to turn °C to °F.