BRZg2/GR86 RaceROM Flex Fuel

Owned by Paul Blamire
Last updated: Nov 04, 2024
10 min read

Introduction:

This strategy utilizes alternative ignition, fuelling, injection and boost maps maps for varying levels of ethanol as well as 2d maps to determine how much of that modification is applied. Typically, ~40% extra fuel will be required for E85 (85% ethanol) to maintain the same Lambda (therefore the same reported petrol AFR), and the transition will be quite linear.

Ethanol content from a sensor can only be read over CANbus and there is no provision for hijacking OEM analog inputs.

Ethanol content ca also be pre-set per mapswitch mode for pre-mixed setups.

Typical Tuning Steps

If the vehicle has already been tuned on E5/10, you can likely math out what your values should be on E0 and E100 knowing the increased fuelling demands and knock resistance of ethanol. For example adding 6 degrees of ignition advance at higher loads down to 0 at light cruise isn’t unknown. The default fuel correction tables will likely be fine in most cases.

Being relatively conservative with the fuelling and ignition timing changes at first is typically the safe course.  After you've confirmed the car runs safely on E10 with the changes you made, Increasing the ethanol content up to ~50% and then verifying it's operation again prior to adjusting fueling/ignition timing.

If you’re sure about the fuel system capacity, you may alternatively fine tune the pump fuel setup before changing to E85 and then checking again midway.

Important Things to Keep In Mind

  • If you define a Flex Fuel input via CAN and the ecu cannot read it (ID is incorrect, absent, or the system isn't plugged in) your flexfuel ethanol content will be 0% but you can use this state to trigger a failsafe

  • Inital Value for Last Known Good Ethanol Reading.  The ethanol value will only update when the vehicle is running, this value is present when the vehicle  isn't running.  As such it is utilised during vehicle starting and is therefore very important to adjust to an appropriate value.

 

Your vehicle should be tuned properly on pump gas (E10 etc.) prior to any tuning on flex fuel.  Any fueling or boost control issues will be made significantly worse as you increase demand and output from the car.  The better the car runs up front, the lower the likelihood of issues cropping up when tuning for higher levels of ethanol (and likely lowering the amount of work and risk overall)

Table of Contents

 

 

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FlexFuel Map List
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FlexFuel Logging Parameter List

 

FlexFuel Maps

FlexFuel Control (RaceROM)

In order to enable the EcuTek RaceROM Flex Fuel system, you'll want to select the appropriate setting for each map switch mode.  If you are using a CAN sensor for FlexFuel it is recommended to use it in all modes since the ECU is self adjusting. The exception to this is if you want to configure an override in case of complete sensor failure.

 

 

FF Fuel Quantity Multiplier

This is the primary table that corrects fuelling for ethanol.

It sets the additional fuel based on ethanol content (0-100%) and coolant temperature.  It would not be unusual to need to add additional E85 when cold due to some unburnt fuel going through the engine.  Pure Ethanol typically requires 60% more fuel to maintain the same lambda (or apparent AFR) as gasoline.  There are no significant changes to injector flowrates when using E85.

If you want to run a richer or leaner AFR when using E85 do not try and compensate with this map as the ECU will use fuel corrections to hit the same target AFR target, instead use FlexFuel Fuel Map and set a a different target AFR.

 

 

FlexFuel Cranking Multiplier

This map is an overall fuel multiplier only used during cranking and uses values similar to FlexFuel Fuel Quantity Multiplier since that map is not applied during cranking.

You may need to use values in this greater that those in FlexFuel Fuel Quantity Multiplier since it is not unusual to need additional E85 when cold due to some unburnt fuel going through the engine. But the defaults will work in 99% of cases.

 

 

 

FF Ethanol Content Hold Load

Particularly with direct-injected vehicles it's not unusual to a slight fluctuation in your sensor readings due to aeration of the fuel.  To minimize the impact of this on your vehicle's operation, the ethanol content employed by the flex fuel strategy can be temporarily locked when your vehicle is operating under high load conditions.  This map sets a load limit.  When this limit as well as the engine RPM level in the FlexFuel Ethanol Content Hold RPM map is exceeded, the flex fuel ethanol content will be fixed at the last value read before the both thresholds were met and until either of two thresholds are no longer met.

 

 

 

 

FF Ethanol Content Hold RPM

In conjunction with FF Ethanol Content Hold Relative Load this can be used to lock the ethanol content when fuel flow is maximised.

 

 

FlexFuel Ethanol Content Fixed Values by Mapswitch Mode

For instances where an ethanol content sensor isn't installed or where it isn't practical, pre-mixed ratios of alcohol can now be catered for in the RaceRom Flex Fuel strategy by entering the ethanol content in this map.  You do so by setting a specific target for each map switch mode. 

Inital Value for Last Known Good Ethanol Reading

The ethanol value will only update when the vehicle is running, this value is present when the vehicle  isn't running.  As such it is utilised during vehicle starting and is therefore very important to adjust to an appropriate value.

 

 

Boost Limit (Ethanol)

Boost limit used when RaceROM boost control is enabled, blended with the regular fuel boost limit using Boost Limit Blend

 

 

Boost Limit Blend

Used to blend the result of the Boost Limit (Gasoline) map and Boost Limit (Ethanol) map. Such that:

  • A value of 0.0 will give the result directly from Boost Limit (Gasoline)

  • A value of 1.0 will give the result direct from Boost Limit (Ethanol)

  • A value of 0.5 will give the boost limit halfway between the two maps.

 

 

Boost Target (Ethanol)

Boost targt used when RaceROM boost control is enabled, blended with the regular fuel boost limit using Boost Target Blend

 

 

Boost Target Blend

Used to blend the result of the Boost Target (Gasoline) map and Boost Target (Ethanol) map. Such that:

  • A value of 0.0 will give the result directly from Boost Target (Gasoline)

  • A value of 1.0 will give the result direct from Boost Target (Ethanol)

  • A value of 0.5 will give the boost limit halfway between the two maps.

 

 

FlexFuel Fuel Map

Adjust this to change the AFR while using ethanol.

This dictates the lambda target the vehicle will target based on the engine load and RPM. 

It's possible to lean out slightly at very high load on pump fuel to a cleaner and crisper value.  However if the base map is made already using a good fuel or even a race fuel that would typically run leaner then it would be entirely possible to want to lower the target AFR when using high levels of E85.

The final AFR target is the result of this map weighted by the result of FlexFuel Fuel Map Blend.

 

 

FlexFuel Fuel Map Blend

 Your final target AFR is not just the value in FlexFuel Fuel Map as this map is used to blend the result from the normal gasoline fuel map and the flexfuel version.

The resulting AFR Target is defined as:

Final AFR Target = FF Target Lambda x FF Target Lambda Blend

So if your normal target was 11:1 and your FlexFuel target was 12:1 and the blend was 0.85 your final result will be 11.85:1

 

 

 

FlexFuel Direct Injection Angle

Use this to run a different start of injection angle for ethanol, typically advancing the injection (higher numbers) up to as high as 400deg BTDC at 7000rpm and 2.0 g/rev to extend the fuel delivery window for ethanol.

This may not be required if using larger port injectors, as you can lean on the port injection system more instead.

 

 

FlexFuel Direct Injection Angle Blend

Blends the output of FlexFuel Direct Injection Angle with the regular gasoline start of injection angle based on the ethanol content.

 

 

FlexFuel Fuel Injection Ratio

Use this to alter the injection ratio for ethanol.

If using large port injectors you may want to use higher values that stock in this map at high load and RPM to reduce the load on the direction injection. However for stock port injectors, it may be beneficial to use moderate values at high load and rpm of around 33%.

 

 

 

FlexFuel Fuel Injection Ratio Blend

Blends the output of FlexFuel Fuel Injection Ratio based on the ethanol content

 

 

 

Flexfuel Ignition Advance 1 (Mode 1,2,3..)

This is the additional ignition timing applied to the base map for FlexFuel. Some additional timing can be added here when tuning for Flexfuel. In the Subaru ignition timing strategy, “Ignition Advance” is the term given to the extra timing added to the base timing based on the value of the Ignition Advance Multiplier which is hopefully 1.0 but can drop when consistent knock is detected and the fuel quality is determined to be poor.

The result of this map blended with the regular fuel result using FlexFuel Ignition Timing Blend in the same way that all the other blend maps work.

 

FlexFuel Ignition Base (Mode 1,2,3..)

This is the main ignition timing base map for Flexfuel, and where most of the additional ignition advance is typically added when tuning the Subaru ignition timing strategy.

The result of this map blended with the regular fuel result using FlexFuel Ignition Timing Blend in the same way that all the other blend maps work.

 

 

 

FlexFuel Ignition Timing AIT Compensation

This is the based ignition timing adjustment for intake temperature and can be varied with ethanol content on the Y axis, it does not use a conventional FlexFuel blend map. However the final change in ignition timing is the result of this map * FlexFuel Ignition Timing AIT Compensation Multiplier it is normal to significantly reduce the retard for high ethanol content as it is less sensitive to knock at high IAT due to its cooling effect.

setting this to 0 will result in significantly retarded ignition base maps to avoid engine knock and reduce power when conditions are favourable.

 

 

FlexFuel Ignition Timing AIT Compensation Multiplier

This multiplies the value of FlexFuel Ignition Timing AIT Compensation so you can reduce the ignition retard typically used at low load and vacuum.

If the result of this map is 0.0 there will be no ignition adjustment regardless of the values in FlexFuel Ignition Timing AIT Compensation so use this to only retard in high load regions especially sensitive to knock.

 

 

 

 

Tuning Tips

  • The most important thing is to start without too many unknowns, don't go from stock fuel system and pump fuel to larger port injectors, and high ethanol concentrations in one step.

  • Add the additional Flexfuel Logging you need to be able to properly see what is happening in the engine and fuel system.

 

Supplemental Content

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