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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.
![nk07oqkdegws9tu5f2n8.jpg]()
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.
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.
![r4cc165ox78o1ebz4wuu.jpg]()
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.
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.
![d3w9evl8rn12e15moepx.jpg]()
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.
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
![59q6areameri5pq4c9dg.jpg]()
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".
![8bop0vvhwi4cr1gjs395.jpg]()
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
![ak2mlu4cb6izvkqzo3zt.jpg]()
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.
![qm4txnjq5fva5erxomle.jpg]()
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%).
![tpmc1lsg94wb6t8ydkdy.jpg]()
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)
![ee1uux1vdu8dvojwdipp.jpg]()
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.
![awf4ro9pbrd5zq7li6rw.jpg]()
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.
![sz5y6ua26w4n0ki3r074.jpg]()
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.
![tbs2iymko5uy810cmavz.jpg]()
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.
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.
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.
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.
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
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".
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
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.
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%).
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)
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.
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.
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.
