Porsche 991 Turbo Accessport Development & Pikes Peak Hill Climb Testing Part 2

With the Porsche 991 Turbo Accessport release growing nearer by the day, we wanted to share some of our findings with the community.  We have been working on the 991 software for quite some time now and have learned a great deal about these cars.  Here, we’ll go over some Accessport basics along with some of the COBB exclusive features that will be available with the 991 Accessport.

Reading/Writing of the ECU

How long does it take?  The initial install of the Accessport takes around 6 minutes.  Once installed, a map change takes approximately 1 minute.

Map changing is done on the Accessport and you can select from calibrations that come preloaded on the device.  We have Stage1 maps that are for otherwise stock cars as well as Stage2 maps that are made for cars with upgraded exhaust systems.  These calibrations come for ACN91, 91, 93, and 100 octane fuels.

We do require that a battery charger be connected to the car for the initial Accessport install process on the 991 turbo.  Once installed, a battery charger is not required for map changes.


A great deal of time and resources have been invested to make sure we are offering an exceptional, feature rich, tuning tool.  One that can not only flash but also allow the end user to monitor the health and status of their car; something that only the COBB Accessport can do!  Data collection is an instrumental part of making a proper calibration.  Without data you are only taking an educated guess of the vehicle’s state.

The Accessport is able to datalog the most crucial parameters for the Engine Control Unit at a sample rate of 40 samples per second.  We currently have the ability to log every single factory monitor as well as a slew of custom created monitors that not even Porsche can see!  As we continue to learn more about these cars, we will have the ability to create custom monitors using any data that is reported to, or calculated by, the ECU.

Below is an example of a small sample of data monitors we currently have access to, viewed in conjunction with a dyno run from one of the many 991 turbos we have been testing with:



Over the previous months we have flown around the country and tested our OTS maps for these cars in varying climates and elevations using a variety of fuel grades.  A majority of the R&D was performed out of our COBB SoCal facility which has access to some very poor quality 91 octane fuels as well as 100 octane race fuel.  We have also performed a great deal of testing in extreme climates and elevations.  From a freezing Pikes Peak to an extremely hot and humid Puerto Rico, we were able to test the cars and calibration files in a variety of relative air densities.  Below, we’ll take a look at a few of the quirks we’ve learned along the way.

First, the factory intercoolers leave much to be desired even in stock form.  With raised boost pressure we have seen intake temps as high as 185*F while in Puerto Rico and 205*F on Pike Peak pushing the pressure ratio of turbos in an extremely low barometric pressure environment.  Intercoolers will be a highly recommended upgrade for these cars in the future as cooling the intake charge will be absolutely vital for making power in a safe manner.

The fuel system on the 991 Turbo seems to be a bit more capable than that of the previous 997.2 Turbo.  We have experimented with alternative fuel mixtures and thus far have had great results.  We have successfully tested up to E30 in a Stage2 Turbo S without any issues whereas the direct injection fuel system on the 997.2 Turbo car is not capable of maintaining pressure with that amount of ethanol content.  We will continue to experiment with alternative fuel blends in order to find and push the limitations of the factory fuel system.

The turbochargers on the 991 Turbo appear to be more efficient than those of the previous generations.  We performed some exhaust gas back pressure testing in the 991 and compared the results to those from a 991.1 Turbo.  We noticed that the 991 spools earlier as well as holds boost longer with less backpressure.  Backpressure is still quite high in the upper RPM range but not as bad as the 997.1.

Below is a dyno plot illustrating the differences between the 991 and 997.1:


The solid line is from the 997.1 and the dashed is from the 991.  The blue line is the barometric pressure (InHg), pink is temperature (*F), red is relative boost pressure (psig), and orange shows exhaust manifold pressure (psig).

You can see that the 991 spools quicker and makes more boost with less back pressure than with the 997.1.  The average boost from 2200RPM to 6500RPM on the 991 in this example was 19.4psi with and average exhaust gas back pressure of 24.2psi.  The average boost for the 997.1 over the same rev range was 17.3psi with an average exhaust back pressure of 24.182psi.  At 6500RPM the exhaust back pressure of the 991 is just shy of 10psi lower than that of the 997.2.  In general, it is preferred to keep exhaust gas back pressure at a minimum in order to keep temperatures under control.  When exhaust gas back pressure is too high it puts excessive strain on the turbocharger and effectively lowers the overall volumetric efficiency of the engine.

Power Gains

The 991 Turbo’s gains on the OTS (Off The Shelf) maps are substantial.


This is a graph of a bone stock 2015 991 Turbo S with just a flash.  As you can see the car picks up a lot all over the power band!  Another strong example of a car we have tuned with some basic bolt-on modifications:


Pikes Peak Hill Climb

In conjunction with our testing we are also helping in calibration for a 991 Turbo S to be run at this year’s Pikes Peak Hill Climb!  The car is Piloted by David Donner who is a long time veteran of the mountain.  We have learned a lot about the cars testing in these conditions and apply all that we learn into our OTS calibrations so out of the box they will work at all elevations and temperatures.

The Porsche’s main competitor this year is Randy Pobst in a Nissan GT-R.  This should prove to be a great race and competition between the two veteran drivers as the cars are very evenly matched!  And, both are on Accessports!


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