E85 Tuning Strategies
ScienceofSpeed, LLC
E85, or FlexFuel, has become popular with performance enthusiasts. In addition to its environmental benefits, the fuel allows high performance engines to operate at higher cylinder pressures producing more power due to ethanol's charge air cooling and increased anti-knock properties. ScienceofSpeed has prepared this summary of tuning strategies for E85 FlexFuel for customers interested in using this fuel.
E85, or FlexFuel, is an abbreviation for a fuel blend of approximately 85% ethanol and 15% gasoline - however the exact ratio can vary significantly based on locale and season. ASTM 5798 specifies that fuel may be labeled as E85 even with an allowable ethanol content of 51-83%.
Ethanol contains less energy by volume compared to gasoline. Having a way of monitoring the content of ethanol in the fuel to adjust for fuel delivery volume is critical for reliable operation of the engine. Vehicles you may have seen labeled with "FlexFuel" badges are supplied by the original manufactures with a fuel composition sensor. The sensor produces an electrical signal which varies depending on the content of ethanol in the fuel.
For performance applications, due to the variance of ethanol content out of the pump, simply draining the fuel tank to switch between gasoline and E85 is not sufficient for reliable operation of the engine. Popular aftermarket engine management systems from AEM and Haltech (with others in development) now allow these same fuel composition sensors to be integrated to the ECU for monitoring and adjusting injector pulse width (the fuel volume supplied to the engine), ignition, and boost pressure to allow seamless adjustment between fuels. ScienceofSpeed offers complete plug-and-play E85 FlexFuel Sensor Systems designed to allow the sensor to be integrated into vehicles not originally equipped with FlexFuel sensors.
ScienceofSpeed E85 FlexFuel System - NSX, all years
Two considerations should also be made when deciding to use E85 fuel. The first is your fuel system. Your fuel system must be up to the task of supplying approximately 30% more fuel volume for the same horsepower as gasoline. Calculators available from websites such as RC Engineering (http://www.rceng.com/technical.aspx) can be used to gain an idea of your fuel requirements. Generally, we have found a BSFC value of .73-.80 can be used for efficient Honda engines. For an example, a NSX 6 cylinder engine producing 600 BHP horsepower with E85 at a BSFC of .78, an injector duty of 80%, and a fuel rail pressure of 56 PSI would require 903 cc/min per injector and 325 L/hr of net fuel flow. Injector sizing and fuel pump capacity should be chosen based on these calculations. Secondly, due to ethanol's corrosive nature, the fuel system's various components must be chemically compatible with ethanol. While many modern OEM fuel systems are designed for some amount of ethanol content, not all are specifically designed for high concentrations of ethanol. Fuel system components should be verified to be compatible and the frequency of fuel system inspection should be increased.
To tune the engine for use with gasoline and E85, two separate calibrations will be performed by tuning for one extreme of minimal ethanol and one extreme of maximum ethanol content. The engine management system will then automatically interpolate between these extremes depending on varying content of ethanol in the fuel.
It must be first considered that most gasoline available from the pump is "oxygenated" or containing around 10-15% ethanol. In addition, "E85" from the pump can vary in ethanol content, usually around 70-85%. Ideally, non-oxygenated 91 octane (R+M)/2 gasoline (0% ethanol) and neat (~100%) ethanol would be used. Non-oxygenated 91 octane fuel is available from retailers such as marine stores. 98% fuel ethanol, sold as E98 is available from retailers such as Ignite Fuels. E98 can be relatively expensive due to the costs of shipping a flammable fluid like this (a 55 gallon drum for example costs around $3-4 / gallon for the fuel, but with shipping, the costs can easily be $10-12 / gallon). Although it can come at a great expense, tuning with E98 is a one time operation to verify that your engine will be tuned properly and is worth the investment. ScienceofSpeed stocks E98 - and your tuner may as well.
The frequency based composition sensor used by ScienceofSpeed is powered by +12V and ground by the ECU. The sensor outputs a varying digital square wave frequency and pulse width. The engine management system interprets this signal to an ethanol content percentage and fuel temperature (temperature is used by some ECUs to correct for sensor accuracy at ethanol content percentage extremes). The AEM EMS (Series 2) must be updated to v02x01 or later firmware and AEMTuner software must be v3.2 or later. The ECU must be setup to indicate which input is used for FlexFuel content (AEM EMS: FlexFuel tab, options window). ScienceofSpeed uses the default switch input "Switch 2". The Rising and Falling Edge options must be turned On (in this example Sw2 Rising Edge and Sw2 Falling Edge are set to On). If these options are not on the options window in your workspace, right click the options window and add them from the list.
Two separate calibrations will then be made. We suggest completing a tune with fresh 91 octane gasoline first since this is most likely to already be in the fuel tank. Then, completely drain fuel tank and replace fuel with E85 (preferably E98). Options for FlexFuel (Crank Advance and Failsafes) must be configured, and separate fuel & ignition tables for FlexFuel will then be configured (see ECU manufactures instructions for details - AEM EMS: http://tinyurl.com/lsusfzx). After tuning and setup is complete, it may be ideal to then vary ethanol content by adding gasoline to decrease ethanol content and verify engine operation. Once configured, the driver can then use any concentration of gasoline or E85 and the ECU will automatically vary fuel delivery, ignition, and boost pressures.
ScienceofSpeed, LLC
E85, or FlexFuel, has become popular with performance enthusiasts. In addition to its environmental benefits, the fuel allows high performance engines to operate at higher cylinder pressures producing more power due to ethanol's charge air cooling and increased anti-knock properties. ScienceofSpeed has prepared this summary of tuning strategies for E85 FlexFuel for customers interested in using this fuel.
E85, or FlexFuel, is an abbreviation for a fuel blend of approximately 85% ethanol and 15% gasoline - however the exact ratio can vary significantly based on locale and season. ASTM 5798 specifies that fuel may be labeled as E85 even with an allowable ethanol content of 51-83%.
Ethanol contains less energy by volume compared to gasoline. Having a way of monitoring the content of ethanol in the fuel to adjust for fuel delivery volume is critical for reliable operation of the engine. Vehicles you may have seen labeled with "FlexFuel" badges are supplied by the original manufactures with a fuel composition sensor. The sensor produces an electrical signal which varies depending on the content of ethanol in the fuel.
For performance applications, due to the variance of ethanol content out of the pump, simply draining the fuel tank to switch between gasoline and E85 is not sufficient for reliable operation of the engine. Popular aftermarket engine management systems from AEM and Haltech (with others in development) now allow these same fuel composition sensors to be integrated to the ECU for monitoring and adjusting injector pulse width (the fuel volume supplied to the engine), ignition, and boost pressure to allow seamless adjustment between fuels. ScienceofSpeed offers complete plug-and-play E85 FlexFuel Sensor Systems designed to allow the sensor to be integrated into vehicles not originally equipped with FlexFuel sensors.
ScienceofSpeed E85 FlexFuel System - NSX, all years
Two considerations should also be made when deciding to use E85 fuel. The first is your fuel system. Your fuel system must be up to the task of supplying approximately 30% more fuel volume for the same horsepower as gasoline. Calculators available from websites such as RC Engineering (http://www.rceng.com/technical.aspx) can be used to gain an idea of your fuel requirements. Generally, we have found a BSFC value of .73-.80 can be used for efficient Honda engines. For an example, a NSX 6 cylinder engine producing 600 BHP horsepower with E85 at a BSFC of .78, an injector duty of 80%, and a fuel rail pressure of 56 PSI would require 903 cc/min per injector and 325 L/hr of net fuel flow. Injector sizing and fuel pump capacity should be chosen based on these calculations. Secondly, due to ethanol's corrosive nature, the fuel system's various components must be chemically compatible with ethanol. While many modern OEM fuel systems are designed for some amount of ethanol content, not all are specifically designed for high concentrations of ethanol. Fuel system components should be verified to be compatible and the frequency of fuel system inspection should be increased.
To tune the engine for use with gasoline and E85, two separate calibrations will be performed by tuning for one extreme of minimal ethanol and one extreme of maximum ethanol content. The engine management system will then automatically interpolate between these extremes depending on varying content of ethanol in the fuel.
It must be first considered that most gasoline available from the pump is "oxygenated" or containing around 10-15% ethanol. In addition, "E85" from the pump can vary in ethanol content, usually around 70-85%. Ideally, non-oxygenated 91 octane (R+M)/2 gasoline (0% ethanol) and neat (~100%) ethanol would be used. Non-oxygenated 91 octane fuel is available from retailers such as marine stores. 98% fuel ethanol, sold as E98 is available from retailers such as Ignite Fuels. E98 can be relatively expensive due to the costs of shipping a flammable fluid like this (a 55 gallon drum for example costs around $3-4 / gallon for the fuel, but with shipping, the costs can easily be $10-12 / gallon). Although it can come at a great expense, tuning with E98 is a one time operation to verify that your engine will be tuned properly and is worth the investment. ScienceofSpeed stocks E98 - and your tuner may as well.
The frequency based composition sensor used by ScienceofSpeed is powered by +12V and ground by the ECU. The sensor outputs a varying digital square wave frequency and pulse width. The engine management system interprets this signal to an ethanol content percentage and fuel temperature (temperature is used by some ECUs to correct for sensor accuracy at ethanol content percentage extremes). The AEM EMS (Series 2) must be updated to v02x01 or later firmware and AEMTuner software must be v3.2 or later. The ECU must be setup to indicate which input is used for FlexFuel content (AEM EMS: FlexFuel tab, options window). ScienceofSpeed uses the default switch input "Switch 2". The Rising and Falling Edge options must be turned On (in this example Sw2 Rising Edge and Sw2 Falling Edge are set to On). If these options are not on the options window in your workspace, right click the options window and add them from the list.
Two separate calibrations will then be made. We suggest completing a tune with fresh 91 octane gasoline first since this is most likely to already be in the fuel tank. Then, completely drain fuel tank and replace fuel with E85 (preferably E98). Options for FlexFuel (Crank Advance and Failsafes) must be configured, and separate fuel & ignition tables for FlexFuel will then be configured (see ECU manufactures instructions for details - AEM EMS: http://tinyurl.com/lsusfzx). After tuning and setup is complete, it may be ideal to then vary ethanol content by adding gasoline to decrease ethanol content and verify engine operation. Once configured, the driver can then use any concentration of gasoline or E85 and the ECU will automatically vary fuel delivery, ignition, and boost pressures.
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