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COBB Flex Fuel For GTR

COBB Flex Fuel programing and proper calibration ensures optimal and engine power at a full range of ethanol concentrations without the inconvenience of actively switching fuels. Full ethanol dependence of timing, fuel target, injector scaling, and boost control creates a final calibration that elegantly responds and adapts to ethanol changes. The only discernment of any response to increased ethanol content is simply increased power. Using this tuning approach, you never have to worry about ethanol content.

COBB Flex Fuel - Dynamic Calibration Adjustment for Ethanol Content - MORE ethanol = more power.

The figure below presents primary data from a 2009 USDM GT-R with GT2867 stock location turbochargers, built motor, camshaft, fuel system upgrades and 2000cc injectors. Using a finished COBB Flex Fuel calibration we tested the car within one hour at using 19% ethanol fuel and 77% ethanol. The graph clearly shows that this car made significantly more power at higher ethanol content compared to low (Panel A). These two test were run at nearly identical boost levels (Panel B) to demonstrate how integrated and ethanol dependent calibration changes in ignition timing (Panel C), and Air fuel target (Panel D) work together to create an ideal calibration across ethanol content and produce more power as ethanol concentration increases. COBB flex fuel dynamically calculates the best injector scalar to deliver precise quantities of fuel regardless of ethanol concentration. Fuel delivery and Injector duty cycle increase as ethanol content increases (Panel E). This drastic change in IDC occurs dynamically with no needed calibration changes using COBB Flex Fuel custom programing.

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Flex fuel tuning guide the short version:

For those of you who are really into the details and already familiar with our software here is an abbreviated version of the tuning guide.

  • Video tutorial by Tim Bailey here
  • Tuning guide here
  • Protuner download here

The addition of new Flex Fuel capability leaves other GT-R tuning parameters unchanged. All but one tuning table related to flex fuel is contained in the "Flex Fuel" tuning folder and each table is considered "base" table meaning that the ECU must be flashed in order for changes to be saved.

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The basic tuning approach for Flex Fuel allows the calibrator to blend a tune for low ethanol and a tune for high ethanol. In order to accomplish this blending the car must be fully tuned on two fuels with very different ethanol concentrations. The finished product of these two distinct tunes is then combined within the flex fuel tables and the switchable maps.

Step 1) - Tune for fuel one and note the ethanol concentration. Use standard real time tuning tables and store your finished tune within the switchable maps as is customary.

Step 2) - Tune for fuel two and note the ethanol concentration. Use standard real time tuning tables and store your finished tune within the switchable maps as is customary.


Step 3) - Combine the two calibrations in one file.

  • At this point you must segregate the two calibrations. The fuel (high or low ethanol) that is most commonly used in the car should be stored in the switchable map slots. Because there are 9 separate map slots within any calibration this will give your final tune the greatest flexibility for the end user.
  • Tuning parameters for the secondary fuel are stored in the "flex fuel" base table section.
  • Either High or Low ethanol calibration parameters can be stored in the "flex fuel section". Indicate the identity of these tables by selecting " 1 or 0" in the flex fuel table "Fuel for RT". The longer definition for this table is "fuel for real time", or alternatively you can think of this as the primary fuel. The primary fuel calibration parameters reside within the 9 switchable map slots (0-8) and are available within "real time" while connected to a live ECU.

Step 4) Calculate injector scalar for 0 and 100 percent ethanol. Using your two known ethanol concentrations along with their paired injector scalar from the two separate high and low ethanol concentrations you can calculate the theoretical scalar for 0 and 100% ethanol. The proportion of these two different injector scalars for the final calibration varies in a linear manner along with ethanol content.

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For your convenience we have constructed an excel worksheet that will quickly allow you to calculate the 0 and 100 percent ethanol injector scalars based upon your two known conditions.

  • Download injector workbook here.

Determining the proper injector scalar: Example COBB 1000cc injectors on car.

Tune 1) 10 % ethanol content and final injector scalar of 980
Tune 2) 77% ethanol content and final injector scalar of 702

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So the values to put into this Flex Fuel calibration are 1021 for low ethanol and 607 for high ethanol.

This particular GT-R uses high ethanol fuel for most of the time and low ethanol rarely. As a result the "Fuel type for RT" is set to "1".

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The math behind the injector scalar is simple and allows the active injector scalar to vary linearly based upon observed ethanol content. For example the active injector scalar at an ethanol concentration of 50% = 50% of e100 injector scalar (303.5) + 50% of e0 injector scalar (510.5) = 814
% ethanol

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Step 5) Set ethanol based blending for each major tuning parameter.
Each of the tables within the "flex fuel" tables is paired with a separate ethanol blending table.

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Final Ignition timing (Fuel target and Cranking Enrichment) are determined by a blend of high and low ethanol tables values and weighted according to ethanol concentration.
This example shows the relationship of high and low ethanol ignition timing tables in this particular finished calibration. From 0 to 20% ethanol ignition timing values from only the low ethanol map are used. Above 70% ethanol the full values from the high ethanol timing map are used. Between 20 and 70% ethanol final ignition timing is a weighted proportion of these two tables highlighted in yellow. For example, at 60% ethanol final ignition timing = (low ethanol timing *50%)+ (high ethanol timing *50%).

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Step 6) - Boost control and Flex fuel. Flex fuel adds a third table that allows the tuner to transform wastegate control based on ethanol content.
Flex fuel code maintains the 9 separate potential user selectable boost levels contained within the switchable map slots. Some tuners will choose to allow the end user to select boost irrespective of ethanol concentration. However, others will additionally choose to use the ethanol based wastegate duty cycle multiplier to offset boost based on ethanol content.
Final wastegate duty cycle = (Waste Gate Duty Cycle)*(Gear and throttle wastegate Multiplier)*(Flex Fuel WGDC multiplier)

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Final wastegate duty cycle can be manipulated as a function ethanol content. In this example the final wastegate duty cycle is unaltered and determined by two primary boost control tables from 0 to 55% ethanol content (multiplier is set to 100%). However above 55% ethanol content the final wastegate duty cycle is creased with a final offset of +20% at 85% ethanol and above. For example, if "gear and throttle wastegate multiplier" and "wastegate duty cycle" tables indicate a wastegate control of 50%, an observed ethanol content of 85% or above will transform the final wastage value by +20% or a final value of 60% WGDC. The most common use of this ethanol based offset will be to increase boost at high ethanol.

Mechanical and electrical Configuration for Flex Fuel
Install any popular flex fuel sensor on the return fuel flow lines as below.

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Most ethanol sensor sensors use a frequency output. You will need to convert this frequency to a 0 to 5V analog signal. Several manufacturers offer these signal conversion devices and several COBB Flex fuel cars use the Zeitronics gauge that includes a 0 to 5 V output. This is noted in the photo with a red circle. The ethanol sensor and lines shown above are highlighted in yellow below.

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The analog input for the fuel 0 to 5 volt signal is the Air Pump Mass Air Flow sensor. The diagram found below illustrates how to wire this Zeitronics gauge and sensor.
Wiring diagram can be downloaded here.

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Just making sure i add a place holder for anything i forgot in the post above.... i also wanted to thank all the COBB Protuners who helped and offered advice related to the development of this new feature.

Sean Ivey of Iveytune in NJ
MIke Botti
AMS
Extreme Turbo Systems
English Racing in Camas WA
Buschur Racing in Wakeman Ohio
Topspeed Motorports in Atlanta GA
Switzer Performance in Northern Ohio
Weapons Grade Performance
Kaizen Tuning
JR Tuned
Induction Performance
JMS in Houston
FFTEC in Hayward CA
Addiction Perforamance in CO
The Boost Creep in CO
Clark Turner Tuning - AZ
Dyno Comp - AZ
Good Speed - AZ
BTA Performance - Sydney Australia
Croydon Racing Developments - Sydney Australia
EQ Tuning - Sacremento CA
SP Engineering - CA
Ben Linney of GTC - UK
MachV - VA
CBRD - PA
Vex Performance - Canada

And many many others.... thanks for your feedback and patience.
 

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Great to know! I'll be talking with SPE this week about this for the one car.

Sent from my Galaxy Note 3 using GT-R Life mobile app
 

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Glad to have been apart of this! This is really awesome stuff!
 

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Great work Cobb!!!! Looking forward to more releases in the near future to put you back at the top......
 

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So now does e85 become flex fuel. What I mean by that is if you flex fuel tune, In that tune is calibrations for up to e85.

Just wondering why I need to pay 800.00 for two tunes.
 

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Great work guys! I have a few cars that have been running on the Beta software for a while now with no issues. Happy to see its now available for the masses


I'm also excited for the release of some of the new safety features we discussed!

Thanks
-- Ed
 

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So now does e85 become flex fuel. What I mean by that is if you flex fuel tune, In that tune is calibrations for up to e85.

Just wondering why I need to pay 800.00 for two tunes.
Completing a full flex fuel tune is like doing 2+ tunes. You have to tune on both plain pump gas (E0-10), full E85, and also ideally test blending at various ethanol concentrations. Because of this, the resulting tune is actually a bit more complicated than simply tuning a pump gas map and an E85 map. The payoff to the customer is in the form of convenience and safety in that you don't have to select from various maps and worry about ethanol concentration in general.

Thanks
-- Ed
 

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Completing a full flex fuel tune is like doing 2+ tunes. You have to tune on both plain pump gas (E0-10), full E85, and also ideally test blending at various ethanol concentrations. Because of this, the resulting tune is actually a bit more complicated than simply tuning a pump gas map and an E85 map. The payoff to the customer is in the form of convenience and safety in that you don't have to select from various maps and worry about ethanol concentration in general.

Thanks
-- Ed
Sorry for the newb question, but do you have to change maps each time or does the Cobb Flex Fuel do this for you.
 

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Completing a full flex fuel tune is like doing 2+ tunes. You have to tune on both plain pump gas (E0-10), full E85, and also ideally test blending at various ethanol concentrations. Because of this, the resulting tune is actually a bit more complicated than simply tuning a pump gas map and an E85 map. The payoff to the customer is in the form of convenience and safety in that you don't have to select from various maps and worry about ethanol concentration in general.

Thanks
-- Ed
Ok but I already am tuned on plain pump. I'm full boltons so I don't need another pump tune.

Nothing will be added in the for of parts other than flex fuel hardware.
 

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Sorry for the newb question, but do you have to change maps each time or does the Cobb Flex Fuel do this for you.
We set it up so there is 1 boost setting for pump gas which automatically gets selected based on the ethanol content and multiple boost settings selectable via the cruise control switch for ethanol.
 

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We set it up so there is 1 boost setting for pump gas which automatically gets selected based on the ethanol content and multiple boost settings selectable via the cruise control switch for ethanol.
Ok cool. Thanks for the reply. Just trying to understand it so I can help others....
 

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Great news.....it's Ivey timeeee
 

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Perhaps there should be a basic FAQ for people new to flex fuel...

Will I be able to run 91 octane gas on FF tune or is it better to have a separate map specifically for pump gas? Is there a difference between the 2 tunes in terms of performance and reliability?

What are the additional mods needed for FF setup? Are there additional maintenance required?

From reading above, there will be 1 boost setting on pump gas and multiple boost settings for e85? Is there a way to set boost for both e85 and pump gas?
 

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So now does e85 become flex fuel. What I mean by that is if you flex fuel tune, In that tune is calibrations for up to e85.

Just wondering why I need to pay 800.00 for two tunes.
This type of tuning allows your car to run on ANY ethanol concentration with just one calibration on the ECU. The calibration dynamically adjusts to whatever ethanol concentration you've got in the tank. No more worries about switching fuel types and having too little or too much ethanol in the tank. A COBB flex fuel tune will run on anything from 0 to 100% ethanol.

Tim
 

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Perhaps there should be a basic FAQ for people new to flex fuel...

What are the additional mods needed for FF setup? Are there additional maintenance required?
You can download the tuning guide in the link from my original post. There is a wiring diagram with all the parts right there... for the DIY guys. If you want to buy a kit i recommend the GotBoost kit as its a full plug and play solution with very high quality components.

http://www.gtrheritage.com/topic/2337-sneak-peek-the-ultimate-flex-fuel-setup-unveiled/

Last boost levels - up to 9 different boost levels that can vary as a function of ethanol content. Just ask your tuner.

maintenance? Just make sure the lines aren't leaking and do a sanity check to make sure the ethanol sensor input is accurate.... luckily you can use your handy Accessport to display ethanol content LIVE!!

Tim
 
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