Coming from Colorado, do any of you turbo guru's know if a turbo can compensate for loss of power due to altitude? Also is a larger turbo more effective? When I drive in the mountains at 8000 plus feet my loss of hp on a non turbo is greater than 25%, anyone know what it would be in a forced induction vehicle? Thanks

 

The 996 Turbo provides boost above atmosphere, so as you gain altitude the boost remains true to the boost mapping until you get to the maximum altitude the turbos can physically keep the boost.

Turbos loose less power with altitude versus non-turbo cars.

 

This is true but the thinner air a high altitude makes the turbo work more to keep the boost the same as they would at 2000 feet. I Live at 7000 feet and have not had a problem with my car, but I trached my turbos on my S4 at the same elivation.

 

My experience at 6500 ASL says that I run fast because the lower Cd (thin air) benefit is greater than the power loss. Obviously not true of NA machines.Hope that helps.

R

 

I have recently moved to Denver and am now experiencing "altitude power loss shock". Here is a real quick break down as I have discovered. A normally aspirated motor loses about 18% of it's power here in Denver, a supercharger loses 8% or so and a turbo will lose about 3%. So while the turbo does lose a bit it is nowhere near what the NA cars suffer. Also a bigger turbo will have more lag which will be amplified at altitude.

 

Unless specifically programmed not to do so, a turbo motor will allow the turbocharger wheel to spin ever faster to compress the ever thinner air to achieve the original target boost. I know that a 944 turbo (electronically controlled wastegate) allowed full boost to 8000 ft (no power loss) then finally the DME would taper off as the altitude increased further - of course the turbo takes longer to achieve the same boost levels since its having to reach higher rpm's.

I would be very interested to know how a stock 996TT handles altitude - is it full boost to 8000 ft as the old 944?

Electronic controls notwithstanding, it only stands to reason that a stock 996TT with its modest boost (0.75 bar max) would have much more turbo wheel rpm "headroom" to compensate for the altitude than a chipped car using the same turbo - it makes you wonder how many of the aftermarket companies have taken into consideration that the high boost turbos (even with diff turbos) may reach overspeed RPMs at altitude much sooner than stock since boost is SO much higher. Did they alter the stock DME software code in the TT to address the (new) RPM limitations of the (new) particular turbo setup at the (new) boost level?

Bond

 

Porsche rates the car as capable of pulling full boost up to something like 8500 feet.

I notice that I pull .9 a bit more often with a stock 996TT than I do while down near sea level.

The car is one of the few I have driven in Denver where the difference between sea-level and 5280 is not really noticeable at all.

 

Stock 996TT w/more HP @ 8500 ft than CGT?!

For every 1000 feet you climb above sea level, there is a reduction in air density of approximately 4.5 percent

Source:

http://www.bassandwalleyeboats.com/s..._page_175.html

Let's see

Carrera GT = 612 hp @ sea level

less (5.280 x 0.045) = 0.2376 or 145 hp, netting 466 hp in Denver
less (8.500 x 0.045) = 0.3825 or 234 hp, netting 378 hp

At 7153 ft, both stock 996TT and CGT net 415 hp - the beauty of turbo charging!

Bond

 

Steve do you see 0.9 on the 415 hp (non X50) 996TT?, Under what conditions? - I am hard pressed to see 0.8 (have seen it a few times very briefly over the past 2500 miles) - mostly 0.6 - 0.7 though........

Bond

 

The car is an 02, non X-50 stock 996 Turbo.

In St Louis I generally see .6 max boost with the occasional .9 spike (never really anything in between, and .9 flashes by almost before you realize).

In Denver I would see .9 around town under full throttle for what I believe was a longer spike. It could be my imagination or it could be the turbo's trying to compensate for the lack of oxygen.

 

Thanks to all for the response. Bond your point on tuning is exactly the reason for my question. My 03 x-50, consistently shows .9 boost and I was hopeful that it was still making most of its power here at 5000 ft. I have considered a chip but I have concerns if the programming would work as advertised at this altitude. My car certainly feels strong but I have never driven a turbo at sea level so I have no comparision. Any tuners have any views? Fish

 

Hi all, I've been giving this issue of altitude some thought recently (living in Colorado myself!). It seems to me that the turbo controls probably operate on a pressure differential between the outside air and full boost, unless they have an altimeter of some type. If the turbo controls are based upon pressure differentials, then it seems to me that a turbo car would lose the same amount of HP as a normally aspirated one. Any comments?

Sincerely,
Paul Rubin
prubin@equilter.com

 

Not true. Evidence of this is supported in the fact that blown and turbocharged cars still manage to run 9/10's of what they are capable of in terms of 1/4 mile timesat sea level at Bandimere here in Denver.

 

Thank you Steve,

Do you know if there's any published data on the Bandimere turbo runs? How close to top performance were they getting?

Sincerely,
Paul Rubin
prubin@equilter.com