COBB AP take into account over spinning the turbos at high altitude?

[RabbidSasquatch]

I noticed at my altitude which is around 5200 ft, im holding boost at about 26 psi (WOT) and sometimes shift spikes to 28-32 psi.Im only on stage 1 on the 91 octane map. The only thing im concerned about is since cars at high altitude try to achieve full boost by boosting higher psi, could this overspin my turbos or is their a safety limit set in the CObb Ap to potentially avoid over spinning the turbo due to higher psi compensation which would cause excessive wear on the turbo at high altitude?

[MilehighM3]

My limited experience with the ap @6k feet only shows a peak of 17-18. What kind of gauge are you using that shows that boost reading?

[1speedbike]

Woah... 32 psi... that cannot possibly be correct

+1 to Bmw135er's question.. what boost gauge are you using? is it calibrated?

The ECU should automatically adjust for the altitude in stock form, so I'm sure Cobb took that into consideration with their reflash.. but 32 psi just seems crazy. I'd ask them. Good luck!

[ErvGotti]

+1 on your guage not being calibrated. You'll need to do a log.

[dfv2]

datalog this with the AP and post the csv file for review.

[Turbolader]

32 psig or 32 psi?

32 psi - (Standard air pressure @ 5200ft ~ 12.3psi) = 19.7 psig.

While still a little bit higher than I would expect, much more believable. If your barometer was high on that day, then your air pressure would have been higher, meaning the effective air pressure of the turbos were lower than 19.7 psi.

[moveswiftly]

Originally Posted by RabbidSasquatch

I noticed at my altitude which is around 5200 ft, im holding boost at about 26 psi (WOT) and sometimes shift spikes to 28-32 psi.Im only on stage 1 on the 91 octane map. The only thing im concerned about is since cars at high altitude try to achieve full boost by boosting higher psi, could this overspin my turbos or is their a safety limit set in the CObb Ap to potentially avoid over spinning the turbo due to higher psi compensation which would cause excessive wear on the turbo at high altitude?

Could be making 16psi at 5200, but still thats a LOT of boost. The engine is probably pulling back timing like hell. I think your PSI is off by 10 lol. But yeah log it and compare it...

[RabbidSasquatch]

I was reading the psi from the Boost gauge in the Cobb ap itself and i'll post the csv graph in a couple more mins.Just from reading the tables on the csv file, I noticed that im holding boost at around 14-15 psi and occasional spikes to 22 psi , but for some reason my boost (psi) reading from the COBB ap shows the exact same numbers that the requested boost is showing. The graph is attached now.

[sluflyer06]

Red line is absolute pressure (atmospheric+boost).

[COBB Tuning]

There are two kinds of boost readings. Relative and Absolute.

Absolute is Manifold pressure + Ambient pressure. Which is what you are logging. So this adds the pressure the turbo is making with the atmosphereic pressure that you feel everyday. This is NOT what most people refer to as "boost".

Relative pressure is boost pressure relative to ambient pressure. That is, the amount of pressure the turbo is making in the manifold over ambient pressure so Manifold pressure - Ambient= Relative. This is generally what is referred to as boost.

The spike you are seeing has been documented as a "false spike". Basically the throttle plate closing causes a brief pressure spike. This has to do with the MAP sensor's placement in relation to the throttle plate. Go ahead and do a lot with Rel Pressure and you will see actual manifold pressure.

As far as overspinning the turbos, I don't really think this is the case. If the turbos are still within their efficiency range and making usable boost, they are not being overworked per se. Rob was able to find a compressor map for these units, I will see if I can find that, that will tell you if and how the turbos are being overrun.

Travis
COBB Tuning