Turbo boost measured from ambient pressure?

[Dartos]

With the proliferation of turbos I have been reading that turbos don't loose power as altitude increases.

That made me think about what the base line is for a turbo building 10 pounds of boost. It must be from ambient pressure + 10#. Otherwise if it was to a maximum manifold pressure instead of a maximum differential, the amount of boost would actually change with altitude.

Ambient correct?

 

[Wheel House Motorsports]

turbos loose power at elevation, they can just overcome it easier by spinning faster or running more boost.

most gauges are zero'd for X amount of PSI and read above that, they dont adjust to above ambient, so the baseline when the engine is off changes due to temp and altitude and whatnot.

ideally we would all measure PSIG to compare boost being run, as it is the level above ambient. Just an example, my boost gauge reads about 2 psi of vaccum sitting in my room at 6000 feet as it is zerod for lower. so if it says im running 6 psi, that means im running 6 psi above 14.7, but say approx 8 psig due to less pressure at elevation.

 

[AKSNOWRIDER]

one thing for those of you running liquid filled guages..you should crack loose the filler plug at normal riding altitude to equalize the pressure(then retighten)..helps with accuracy(this is what autometer told us years ago when they first came out with liquid filled guages)

 

[HYFLYR]

one thing for those of you running liquid filled guages..you should crack loose the filler plug at normal riding altitude to equalize the pressure(then retighten)..helps with accuracy(this is what autometer told us years ago when they first came out with liquid filled guages)

True!

 

[revpilot]

You're onto it Dartos, good explanation here:http://www.2-stroke-porting.com/altiden.htm

 

[allblowdup]

Most of the OEM turbo sleds work on absolute boost pressure. Meaning that the engine will always see the same amout of boost. At sea level 14.7 + 10 psi boost = 24.7 absolute. At 6000 ft 12.7(approx) + 12 psi boost = 24.7. That is why they say that they do not loose power at altitude. Most after market turbo kits are not like this so you have to turn up the boost the higher you go. You can also get away with more boost.

 

[hatchers]

With the proliferation of turbos I have been reading that turbos don't loose power as altitude increases.

Anything that compresses air (engines/compressors) will loose potential output power when everything remains the same except elevation….and turbo just compresses what air is sucks in, thinner air wont compress as much ad low alt heavy air…its just that simple