B20E & D-Jet: Modern EFI with Classic Appeal

For enthusiasts of classic vehicles, there's an undeniable charm in preserving the original aesthetic, especially under the bonnet. Yet, the allure of modern reliability, improved performance, and enhanced fuel efficiency is equally strong. This presents a delightful conundrum for owners of the venerable B20E engine, famed for its Bosch D-Jetronic fuel injection system. The question often arises: can one upgrade to a more contemporary electronic fuel injection (EFI) system, such as Megasquirt, while meticulously maintaining that cherished stock appearance? The answer, happily, is a resounding yes, though it requires a thoughtful approach and a bit of ingenuity.

The B20E engine, found in various Volvo models from the late 1960s and early 1970s, was a significant step forward in automotive technology with its pioneering Bosch D-Jetronic system. Unlike earlier mechanical injection or carburettor setups, D-Jetronic used electronic control to meter fuel based on manifold pressure, engine speed, and temperature. While revolutionary for its time, the original D-Jetronic system can, after decades of service, become temperamental. Ageing components, vacuum leaks, and the sheer complexity of diagnosing issues can lead to rough running, poor fuel economy, and unreliable starting. This is where modern EFI systems, particularly adaptable ones like Megasquirt, come into their own, offering a precise, reliable, and tuneable alternative.

Embracing Megasquirt While Retaining the Classic Look

The beauty of using a standalone EFI system like Megasquirt lies in its flexibility. Unlike a fixed OEM system, Megasquirt can be configured to work with a wide array of sensors and actuators, making it an ideal candidate for custom installations where maintaining a stock appearance is paramount. For the B20E, the key to achieving this lies in judiciously selecting which original components to retain and which to discreetly replace.

Utilising Stock B20E Components

One of the most appealing aspects of this conversion is the ability to reuse significant portions of the original D-Jetronic hardware. The B20E's original intake manifold is perfectly suited for this purpose. Its design, with individual runners and injector bosses, integrates seamlessly with a Megasquirt system. This immediately preserves a large part of the engine's visual identity.

Furthermore, the stock Bosch injectors themselves can often be retained. These injectors, typically found on the B20E, have a flow rate of approximately 36.15 lb/hr (or 380 cc/min) at 43.5 psi (3 bar). This flow rate is quite generous and often sufficient for all but the most radically tuned B20E engines. Retaining the original injectors means you avoid the need for custom fuel rails or injector adapters, further contributing to the stock look.

Wiring Harness Considerations

Another area where the original aesthetic can be preserved is the wiring harness. If your B20E's D-Jet wiring harness is in good condition, it is entirely possible, with a bit of creative work and knowledge of the pinouts, to adapt it for use with Megasquirt. This eliminates the need for a completely new, potentially conspicuous, wiring loom, keeping the engine bay looking as it should. However, careful inspection for brittle insulation or corroded connectors is essential, as any compromise in the harness integrity could lead to frustrating intermittent faults.

The Subtle Visual Giveaways: What Changes?

While much can be retained, there are a few components that will necessarily change or be removed when transitioning from D-Jetronic to Megasquirt. These are the primary visual giveaways that indicate a non-D-Jet system is in place. Understanding these and planning for their discreet integration or removal is crucial for a truly convincing stock appearance:

• Bosch Intake Manifold Pressure Sensor: The original D-Jetronic system relies heavily on a large, often prominent, Bosch intake manifold pressure (MAP) sensor. With Megasquirt, a modern, much smaller MAP sensor is typically used, which can be mounted remotely or hidden from view, eliminating the bulky original unit.
• Throttle Position Switch (TPS): The D-Jetronic system used a simple, often large, throttle position switch (TPS) for idle and wide-open throttle detection. Megasquirt, for more precise fuelling and better drivability, typically requires a linear throttle position sensor. These modern TPS units are significantly smaller and can often be adapted to the original throttle body linkages with minimal visual impact.
• Cold Start Valve: The D-Jetronic system included a dedicated cold start valve to enrich the mixture during cold cranking. Megasquirt's advanced cold start algorithms and precise injector control render this component redundant. Its removal further cleans up the engine bay.
• Fuel Pressure Regulator (FPR): While the original D-Jetronic system had a fuel pressure regulator, a Megasquirt system will typically require a different, vacuum-referenced fuel pressure regulator. This type of FPR maintains a constant pressure differential across the injectors, regardless of manifold pressure, which is crucial for accurate fuel delivery. This new FPR will have a reference line running to the intake manifold, which might be a visual difference, but modern units are often compact and can be strategically placed.

Minimising Visual Impact

To further enhance the stock look, consider:

• Mounting new sensors in discreet locations, perhaps behind the manifold or low down.
• Using black wiring loom and connectors to blend in with other engine components.
• Carefully routing vacuum lines for the new FPR to be as unobtrusive as possible.

Benefits Beyond Aesthetics

Beyond simply preserving the classic lines of your B20E, migrating to a Megasquirt system offers substantial practical benefits:

• Improved Drivability: Enjoy smoother idle, better throttle response, and more consistent performance across varying temperatures and altitudes.
• Enhanced Fuel Economy: Precise control over fuel delivery optimises combustion, potentially leading to noticeable improvements in miles per gallon.
• Reliability: Modern electronic components are far more robust and less prone to failure than decades-old D-Jetronic parts.
• Tuneability: Megasquirt allows for fine-tuning of every aspect of engine operation, from ignition timing to fuel maps, enabling you to extract optimal performance from your B20E, whether it's stock or has undergone internal modifications.
• Diagnostics: Modern EFI systems offer comprehensive diagnostic capabilities, making troubleshooting far simpler than with the original D-Jetronic.

Comparative Overview: D-Jet vs. Megasquirt (Stock Look)

Installation Considerations and Resources

While the concept is straightforward, the actual implementation requires a degree of technical skill and patience. Key considerations include:

• Sensor Integration: Ensuring the correct modern sensors (e.g., coolant temperature, air temperature, crankshaft position) are properly installed and wired to Megasquirt. Some may require custom mounting solutions.
• Fuel System Upgrades: While the original plumbing can often be reused, it's wise to ensure the fuel pump is up to the task of maintaining consistent pressure for the new EFI system. A modern, quieter, and more reliable EFI-specific fuel pump is often a worthwhile upgrade.
• Tuning: This is arguably the most critical aspect. Megasquirt requires initial setup and subsequent tuning (often referred to as 'mapping') to create accurate fuel and ignition tables for your specific engine. This can be done by a professional tuner or by the owner using wideband oxygen sensors and tuning software.

For those embarking on this journey, valuable resources exist. Notably, there are well-documented conversions, such as Steve Berry's very detailed write-up on his 1800 conversion, which can be found on sites like 1800philes.com. Such resources provide invaluable insights into the practicalities and challenges of this specific modification.

What about AEM Systems?

While AEM offers excellent standalone EFI solutions, there is significantly less public information or documented success stories regarding their implementation on B20E engines compared to Megasquirt. This doesn't mean it's impossible, but it suggests a steeper learning curve and potentially more custom development if you choose that route.

Frequently Asked Questions (FAQs)

Q1: Is this a DIY project, or should I seek professional help?

A1: While a skilled and determined DIY enthusiast with a good understanding of automotive electronics and engine management can undertake this project, it is not for the faint of heart. If you are not confident with wiring, sensor installation, and especially engine tuning, professional installation and tuning are highly recommended to avoid potential engine damage or frustrating performance issues.

Q2: Will this modification pass emissions tests?

A2: This depends entirely on the specific emissions regulations in your region and the quality of the tune. A properly tuned Megasquirt system can often achieve very clean emissions, potentially even cleaner than a worn-out D-Jetronic system. However, some regions have visual inspection requirements that might flag the non-original components. Always check local regulations.

Q3: Can I use different injectors with Megasquirt?

A3: Yes, Megasquirt can control virtually any type of modern fuel injector. While the original Bosch injectors are often sufficient and help maintain the stock look, if you plan for significant power upgrades, you might need higher-flowing injectors. Megasquirt's software allows you to configure injector size and dead time for optimal control.

Q4: How much tuning is typically required after installation?

A4: Initial setup involves configuring the Megasquirt software for your engine's specifics (number of cylinders, injector size, sensor types). After that, the engine will need to be 'mapped' or tuned. This involves calibrating the fuel and ignition tables across various RPMs and engine loads. This can range from basic street tuning to advanced dyno tuning for optimal performance.

Q5: Will this affect my classic car's originality or resale value?

A5: This is a subjective matter. For some purists, any deviation from absolute originality might be seen as a negative. However, for many, a discreetly upgraded classic that offers modern reliability and drivability while maintaining its visual integrity is highly desirable and can even enhance value, especially if the conversion is done professionally and is reversible.

Conclusion

The quest to merge classic automotive aesthetics with modern performance and reliability is a common one among enthusiasts. For the B20E engine, the answer to upgrading its fuel injection system while preserving that cherished D-Jetronic look lies firmly with adaptable standalone EFI systems like Megasquirt. By thoughtfully reusing original components such as the intake manifold and even the Bosch injectors, and by strategically concealing or minimising the visual impact of necessary component changes, it is entirely feasible to achieve a discreet yet powerful transformation. The benefits of improved drivability, fuel economy, and tuneability far outweigh the challenges, making this conversion a truly rewarding endeavour for any B20E owner seeking the best of both worlds.

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