24/10/2025
For many classic car enthusiasts in the UK, the charm of their vintage vehicle lies in its originality and mechanical simplicity. However, the temperamental nature of carburettors – with their susceptibility to temperature changes, altitude variations, and often less-than-optimal fuel economy – can sometimes detract from the pure joy of driving. Imagine harnessing the power, precision, and efficiency of a modern electronic fuel injection (EFI) system, all while retaining the classic aesthetics of your beloved motor. Thanks to innovative developments like the Weber Retroject Throttle Body, this dream is now a remarkably straightforward reality. Converting your classic's carburettor to electronic fuel injection has truly never been easier, offering a seamless blend of heritage and cutting-edge performance.
What Exactly is the Weber Retroject Throttle Body?
At its heart, the Weber Retroject is a brilliantly engineered dual injector throttle body designed for a direct, uncomplicated swap with some of the most common Weber carburettors found on classic British and European cars. Specifically, it's crafted to replace the popular Weber 32/36 DGV and 38DGAS units. This isn't just a generic EFI kit; it's a dedicated solution that respects the original architecture of your engine. The critical dimensions of the Retroject are identical to those of the carburettors it replaces, measuring 86mm in height and featuring mounting stud hole centres of 93mm x 46mm. This meticulous design ensures that the positioning of the throttle lever and its rotation are also precisely matched, eliminating the need for complex modifications to your existing throttle linkages or inlet manifold. In essence, you can remove your old Weber twin-choke carburettor, bolt on the Retroject, integrate it with an aftermarket Engine Control Unit (ECU), a suitable wiring loom, and a high-pressure fuel supply – such as the Webcon WFP600 fuel pump – and instantly elevate your classic's performance into the 21st century.
The Transformative Benefits of EFI Conversion
Upgrading your classic car from a carburettor to an EFI system via the Retroject offers a plethora of advantages that fundamentally improve the driving experience. This conversion isn't just about modernising; it's about optimising every aspect of your engine's operation.
- Enhanced Power and Driveability: EFI systems provide far more precise control over fuel delivery than carburettors. This precision translates directly into improved power output across the entire RPM range and significantly smoother driveability. Gone are the flat spots, hesitant acceleration, and inconsistent performance often associated with carburettors. Your engine will feel more responsive, eager, and refined.
- Superior Fuel Economy: By accurately metering the fuel based on real-time engine conditions – including air temperature, engine load, and RPM – EFI ensures that your engine always receives the optimal air/fuel mixture. This meticulous control dramatically reduces fuel wastage, leading to noticeable improvements in miles per gallon (MPG). Over time, these savings can be substantial, especially for those who enjoy longer journeys in their classic.
- Increased Torque: The improved atomisation of fuel and more efficient combustion delivered by EFI contribute to better low-end and mid-range torque. This means more usable power for everyday driving, making your classic feel more effortless to accelerate and cruise, particularly in modern traffic conditions.
- Effortless Cold Starts: One of the most frustrating aspects of carburettor ownership is often the struggle with cold starts, especially in colder UK climates. EFI systems, with their precise fuel mapping and temperature sensors, eliminate this headache. Your engine will start reliably and run smoothly from the moment you turn the key, regardless of the ambient temperature.
- Improved Reliability and Consistency: EFI systems are inherently less susceptible to environmental factors like changes in altitude or atmospheric pressure, which can wreak havoc on carburettor tuning. Once tuned, an EFI system provides consistent performance day in and day out, reducing the need for frequent adjustments and offering greater peace of mind on the road.
- Potential for Reduced Emissions: While not the primary driver for many classic owners, the more efficient combustion and precise fuel control offered by EFI can lead to lower exhaust emissions. This can be particularly beneficial for kit car builders who need to comply with modern catalyst requirements.
Diving Deeper: Technical Specifications and Installation Notes
The Retroject is supplied as a comprehensive unit, pre-fitted with crucial components that simplify the conversion process. Each unit includes two genuine Weber 480cc/m PICO fuel injectors, a Throttle Position Sensor (TPS), an air temperature sensor, an idle motor (IACV), and a fixed 3 bar fuel pressure regulator. Additionally, it comes with two straight 8mm fuel unions, though 90-degree angled ones are available separately if your engine bay layout requires them.
Wiring Connections: Understanding the wiring is fundamental for a successful installation:
- Air Temperature Sensor: This sensor is not polarity conscious, meaning it can be connected either way without issue.
- Injectors: Each injector connector is clearly marked with '+' and '-' for correct polarity.
- Throttle Position Sensor (TPS): Typically, this will have three connections: 'A' for Ground, 'B' for 5V supply, and 'C' for the Signal output to your ECU.
- Fuel Pressure Regulator: The supplied unit is a fixed 3 bar regulator, ensuring consistent fuel pressure for the injectors.
- Idle Air Control Valve (IACV): This stepper motor-driven valve controls idle speed. It typically has four cavities: 'A' for Coil 1 +ve, 'B' for Coil 1 -ve, 'C' for Coil 2 +ve, and 'D' for Coil 2 -ve.
Customisation and Flexibility: While the Retroject comes with 480cc/m Weber Marelli PICO injectors, it offers flexibility for different engine requirements. If your engine build or tuning strategy demands a different injector size, you can select alternative sizes from the available options. Similarly, while a fixed 3 bar fuel pressure regulator is standard, an adjustable 0-5 bar regulator can be chosen if you require more precise control over fuel pressure for specific tuning or forced induction applications.
Important Installation Considerations:
- IACV Air Feed: The air intake for the Idle Air Control Valve (IACV) is deliberately blanked off during assembly by the top cover gasket. If you intend to utilise the IACV for automatic idle control (highly recommended for modern EFI performance), you will need to open this feed. This is achieved by carefully inserting the shaft of a 3mm drill into the top feed hole until the gasket is punched through, allowing air to pass. If the IACV is not being used, this seal must remain intact.
- Vacuum Take-off for Distributor Advance: The Retroject is supplied without a vacuum take-off point for distributor advance. However, a pre-drilled location is provided in the base of the unit to accommodate an optional vacuum take-off union (part number 1053601400). If this functionality is required, a 1.5mm hole will need to be carefully drilled through to the bore of the unit. The union is a press-fit, and extreme care is paramount during installation to avoid damaging the brass component. A useful tip to aid installation is to place the union in a freezer for a few hours before fitting; the slight contraction will make the press-fit easier.
For a complete installation, you will also need the ATB400CK connector pack, which contains all the necessary connectors to seamlessly integrate the Retroject into your new wiring harness.
Classic Carburettor vs. Modern EFI (Retroject)
To truly appreciate the leap forward that Retroject offers, it's helpful to compare the characteristics of traditional carburettors with those of a modern EFI system:
| Feature | Traditional Carburettor | Electronic Fuel Injection (Retroject) |
|---|---|---|
| Fuel Delivery | Mechanical, Venturi-based, less precise. | Electronic, injector-based, highly precise and metered. |
| Performance | Can have flat spots, sensitive to conditions, less consistent power. | Smooth power delivery, improved throttle response, consistent performance. |
| Fuel Economy | Generally lower due to less precise fuel metering. | Significantly improved due to optimal air/fuel mixture control. |
| Cold Starts | Often challenging, requires choke, prone to flooding. | Effortless and reliable, even in cold weather. |
| Altitude/Weather Comp. | Poor, requires re-jetting or adjustment for changes. | Excellent, automatically compensates for environmental changes. |
| Maintenance | Requires regular cleaning, tuning, and jet changes. | Less frequent maintenance, self-diagnostic capabilities with ECU. |
| Emissions | Higher, less efficient combustion. | Lower, cleaner combustion, can meet modern catalyst requirements. |
| Complexity | Mechanical simplicity, but tuning can be an art. | Electronic system with sensors and ECU, requires initial mapping. |
| Installation | Simple bolt-on, but requires fuel supply & ECU integration. | Direct bolt-on replacement for specific Weber carbs. |
Ideal Applications for Retroject
The versatility and ease of installation make the Retroject an ideal solution for a variety of applications beyond just classic car restoration:
- Classic Car Restoration and Enhancement: For owners who cherish their classic but desire modern reliability, economy, and performance without significant visual alterations to the engine bay. It's a way to enjoy the best of both worlds.
- Kit Car Builds: When installing a modern engine into a kit car, or even retaining a classic engine, Retroject provides a straightforward path to achieving EFI, which is often crucial for meeting contemporary emissions and catalyst requirements.
- Off-Road Vehicles: EFI offers superior performance in extreme angles and rough terrain compared to carburettors, which can suffer from fuel starvation or flooding. Retroject makes upgrading off-road classics much simpler.
- Marine Applications: Similar to off-road use, marine engines benefit immensely from the consistent and reliable fuel delivery of EFI, especially when operating in varying sea conditions where carburettors might struggle.
- Engine Swaps: For those undertaking engine swaps in custom projects, Retroject simplifies the fuel delivery aspect, especially when aiming for a modern, reliable powertrain.
Frequently Asked Questions (FAQ)
Q: Is the Weber Retroject a complete electronic fuel injection kit?
A: No, the Retroject is the throttle body itself, which incorporates the injectors, sensors, and idle motor. You will still need an aftermarket ECU (Engine Control Unit), a wiring loom to connect it, a high-pressure fuel pump (such as the Webcon WFP600), and a fuel return line to complete the EFI system. It provides the crucial physical interface for fuel and air delivery.
Q: Do I need a new fuel pump?
A: Yes, absolutely. Carburettors operate on low fuel pressure (typically 3-7 PSI), whereas electronic fuel injection systems require significantly higher pressure (typically 40-60 PSI or 3 bar for Retroject). You will need to install a high-pressure electric fuel pump and potentially upgrade your fuel lines and add a fuel return line to your tank.
Q: Can I install Retroject myself, or do I need a professional?
A: Mechanically, installing the Retroject is designed to be straightforward for a competent DIY enthusiast, as it directly replaces the existing carburettor. However, integrating it with an ECU, wiring the sensors, and especially tuning the ECU for optimal performance will likely require professional assistance from an EFI specialist, or significant dedication to learning modern engine management principles.
Q: What kind of ECU should I use with Retroject?
A: The Retroject is designed to be compatible with virtually any aftermarket ECU that supports sequential or semi-sequential fuel injection and can manage an idle air control valve (IACV) and standard sensors (TPS, air temp). Popular brands include Megasquirt, Emerald, Omex, and others. The choice often depends on your budget, desired features, and tuning preferences.
Q: Will converting to EFI affect my classic car's originality?
A: Visually, the Retroject is designed to mimic the appearance of a traditional Weber carburettor, so it blends in remarkably well, especially when paired with a period-correct air filter. While it's an internal modification, it allows you to retain the external classic charm of your engine bay while gaining all the benefits of modern EFI. Many consider it a sympathetic upgrade rather than a deviation from originality.
Q: What are the main advantages of Retroject over simply rebuilding my carburettor?
A: While rebuilding a carburettor can restore some performance, it won't fundamentally change its inherent limitations. Retroject offers precise fuel metering, automatic compensation for environmental factors, improved fuel economy, reliable cold starts, and significantly better driveability and power delivery – none of which a rebuilt carburettor can provide. It's a leap forward in technology, not just a repair.
Conclusion
The Weber Retroject Throttle Body represents a significant step forward for classic car enthusiasts seeking to modernise their beloved vehicles without sacrificing their authentic character. By offering a direct, bolt-on replacement for common Weber carburettors, it simplifies the transition to electronic fuel injection, unlocking a world of improved performance, reliability, and fuel economy. No more wrestling with fiddly chokes, inconsistent idling, or unpredictable power delivery. With Retroject, your classic car can enjoy the driveability, power, and economy of a modern vehicle, while retaining every bit of its timeless appeal. It's an ingenious solution that truly makes the best of both worlds attainable for the discerning classic car owner in the UK.
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