Boost Referenced vs. Non-Boost Referenced: Choosing the Best Fuel System Set-up
Optimizing your E85 motorsport fuel system requires a careful understanding of the differences between boost-referenced (BREF) and non-boost-referenced (NBREF) setups.
This guide provides a clear breakdown of their pros and cons, helping you make an informed decision.
Boost-Referenced (BREF): Precision and Efficiency
* How it Works: Fuel pressure increases proportionally with boost pressure, maintaining a constant pressure difference across the injectors.
* Pros:
* Consistent Fuel Delivery: Ensures precise fuel delivery regardless of boost levels, maximizing power output and preventing damaging lean conditions.
* Simplified Tuning: Provides a linear relationship between fuel pressure and boost, making fuel map calibration easier and more accurate.
* Reduced Fuel Pump Load at Low Boost: Dynamically adjusts fuel pressure, reducing strain on the pump at low boost conditions, improving efficiency, and extending its lifespan.
* Lower Fuel Temperatures: Minimizes fuel heating, reducing the risk of vapor lock, especially critical with E85.
* Enhanced Fuel System Dynamics: Reacts quickly to boost changes, ensuring optimal fuel delivery and improved throttle response.
* Flexible Design: Allows for greater flexibility in system design and component selection.
* Cons:
* Complexity: Requires a boost reference source and specialized regulator, potentially increasing installation and troubleshooting complexity.
* Boost Sensitivity: Susceptible to boost fluctuations from leaks or control issues, which can disrupt fuel pressure regulation.
* Higher Fuel Pump Load at High Boost: At high boost, the fuel pump needs to work harder to provide the increased fuel pressure. This can lead to higher fuel temperatures and potentially shorten pump lifespan.
Non-Boost-Referenced (NBREF): Simplicity, with Trade-offs
* How it Works: Fuel pressure remains constant, leading to a decreasing pressure differential across the injectors as boost increases. This varying pressure differential is further influenced by changes in RPM.
* Pros:
* Simple Setup: Easier to install with fewer components.
* Cons:
* Inconsistent Fueling: Fuel delivery changes non-linearly with boost and RPM, potentially hindering performance and requiring larger injectors to compensate.
* Tuning Challenges: Requires complex fuel maps to compensate for non-linear fuel delivery, making tuning more challenging, particularly across the RPM range. This includes:
* Dead Time Compensation: Accurately mapping injector dead time across varying pressure differentials and RPMs becomes crucial, as dead time is influenced by both factors.
* Fuel Map Adjustments: Creating complex fuel maps that account for the changing fuel flow characteristics at different boost levels.
* Injector Characterization: Precisely characterizing injector flow behavior across a wider range of pressure differentials and RPMs. This often involves extensive data logging and analysis to map the non-linear relationship between pulse width, pressure differential, and fuel flow. For example, with a constant fuel pressure of 50 psi, a 1ms pulse width might deliver 0.05 grams of fuel at a low boost of 5 psi (45 psi differential), but only 0.04 grams at a high boost of 20 psi (30 psi differential). This requires logging injector pulse width and fuel flow data at various boost levels and engine RPMs to create a comprehensive injector characterization map.
* Transient Fuel Compensation: Implementing strategies to address transient fuel delivery issues during rapid changes in boost pressure.
* Increased Fuel Pump Load: Places a constant high load on the fuel pump, leading to increased wear and tear, higher energy consumption, and potential for premature failure.
* Higher Fuel Temperatures: Increased pump workload can lead to higher fuel temperatures, increasing the risk of vapor lock, especially with E85.
* Less Design Flexibility: Offers less flexibility in system design and component selection compared to BREF systems.
Making the Choice
For maximum performance, precise tuning, and efficiency with E85, a boost-referenced system is often the superior choice, mainly due to its consistent and predictable fuel delivery across the operating range, regardless of RPM and boost.
If simplicity is paramount, a non-boost-referenced system is an option, but be prepared to address tuning challenges and potential performance limitations, particularly with the added complexity of RPM-dependent injector behavior.
Choose wisely to unlock the full potential of your E85 motorsport project!
Written by Julian Austin – Founder: Aftermarket Industries