Datsun L-Series EFI Conversion: Your Ultimate Guide

Upgrading a classic Datsun L-series engine, such as the venerable L20B, from its original carburettor setup to modern electronic fuel injection (EFI) is a popular and highly effective modification. While the specific kits detailed here primarily focus on the 6-cylinder L-series engines, the principles, components, and benefits are directly applicable to a 4-cylinder L20B. An EFI conversion, particularly with Individual Throttle Bodies (ITBs), promises significant improvements in throttle response, fuel efficiency, power output, and overall drivability, transforming your classic into a more refined and potent machine.

Why Convert Your Datsun L-Series to EFI?

For decades, carburettors were the standard for fuel delivery in automotive engines. While charming in their simplicity, they often fall short in terms of precision, adaptability, and efficiency compared to modern EFI systems. Converting your Datsun L-series to EFI offers a multitude of advantages:

• Improved Fuel Economy: EFI systems precisely meter fuel based on engine load, RPM, and other environmental factors, leading to more efficient combustion and better mileage.
• Enhanced Performance: With more accurate fuel delivery and the ability to fine-tune for specific modifications, EFI can unlock greater horsepower and torque. ITBs, in particular, provide each cylinder with its own dedicated air intake, optimising airflow and enhancing throttle response.
• Better Drivability: Say goodbye to cold-start issues, flat spots, and inconsistent idling. EFI provides smooth, consistent power delivery across the entire RPM range. The use of 6° throttle plates, as opposed to older 12° designs, significantly improves off-idle and cruise drivability by offering a more linear airflow change at small throttle openings.
• Increased Reliability: Modern EFI components are generally more reliable and require less frequent adjustment than carburettors.
• Tuning Flexibility: An EFI system, coupled with a programmable Engine Control Unit (ECU), allows for precise tuning to accommodate engine modifications, different fuel types, or specific driving conditions.

The Heart of the Conversion: Individual Throttle Body (ITB) Kits

Many Datsun L-series EFI conversions opt for individual throttle body setups due to their performance benefits and classic aesthetic, mimicking the look of high-performance carburettors like Webers. These kits typically include multiple throttle bodies, a manifold, fuel rail, and various ancillary components.

Key Components of an ITB Kit

When considering an ITB kit for your L-series engine, you'll encounter several crucial elements:

Throttle Bodies

The core of the system, these are precision-engineered units. Companies offer sizes ranging from 40mm to 55mm bore diameters. Larger bores generally allow for more airflow and higher peak power, while smaller bores can offer better low-end throttle response. It's vital that every throttle bore and plate are meticulously measured and matched as a pair to ensure consistent airflow across all cylinders, which is paramount for achieving optimal idle and cruise quality.

Professional Grade Manufacture: High-quality throttle bodies are typically manufactured from 601 Cast aluminium, heat-treated, and then CNC machined. Butterflies are precisely machined to extremely tight tolerances (e.g., 0.0005") and secured to centreless ground brass shafts with split screws for reliability. Importantly, modern designs incorporate bearings rather than bushes to eliminate axial shaft movement and provide sharp throttle response.

Intake Manifold

A high-performance intake manifold is designed to perfectly mate the ITBs to your engine's cylinder head. Some kits may utilise specific castings like the TWM intake manifold. Options like manifold port matching and smoothing out the internal runners can further optimise airflow and performance.

Fuel Rail Kit

This component delivers fuel to each injector. Modern kits feature robust designs, such as Pro-Series or 1-piece billet aluminium fuel rails, designed for use with contemporary injectors like Bosch EV6 types. This eliminates outdated injector styles and simplifies plumbing.

Injectors

Choosing the right fuel injectors is critical for proper fuel delivery. Injectors are rated by their flow rate (e.g., cc/min or lb/hr). The provided information gives a helpful guide for naturally aspirated (NA) flywheel horsepower ratings based on injector size:

For boosted applications, it is highly recommended to consult with the supplier or a tuning expert, as fuel requirements increase significantly under forced induction. Kits are typically set up to suit a full-height (60mm O-Ring - O-ring) 14mm O-ring injector if you don't purchase injectors with the kit.

Linkage or Cable System

Traditionally, ITBs used complex linkage systems. However, modern kits increasingly feature cable setups due to their superior user-friendliness and reduced compatibility issues. A well-designed cable system ensures smooth and precise throttle operation.

Air Filtration and Ram Tubes

Air filters are essential to protect your engine from contaminants. Kits often offer various low-profile K&N style filters and matching ram tubes (also known as velocity stacks) to optimise airflow into the throttle bodies. These components are often available in classic black as standard, with options for other colours like blue at a small premium.

Throttle Position Sensor (TPS)

A TPS is vital for any EFI system, providing the ECU with information about the throttle pedal's position. Kits ensure the TPS "D" drive is positioned optimally for your engine.

Fuel System Plumbing & Regulator

Beyond the rail and injectors, a complete EFI conversion requires a robust fuel system. This includes an Aeromotive Fuel Pressure Regulator package (with fittings and pressure gauge) and high-quality EFI-rated fuel hoses capable of handling pressures up to 200psi. Setting up your fuel system correctly the first time is crucial for reliability and safety.

Vacuum System

For a smooth-running EFI system, especially with ITBs, a well-managed vacuum system is necessary. This typically includes a vacuum balance line, a vacuum reserve canister with hoses, and a billet aluminium vacuum distribution block with fittings. These components help ensure stable idle and proper sensor readings.

Boosted vs. Naturally Aspirated Considerations

If you plan to run your L-series engine with forced induction (turbocharger or supercharger), specific modifications are necessary. For example, the lip seals behind the throttle shaft bearings are installed differently depending on whether the engine is boosted or naturally aspirated. For NA engines, they prevent grease from being sucked out, while for boosted applications, they are reversed to prevent boost leakage and bearing grease evacuation.

Assembly Options: Fully Assembled vs. Sub-Assembled

Manufacturers often offer flexibility in how your ITB kit is supplied:

• Fully Assembled Kit: Each throttle body is precision factory assembled. Throttle shafts are cut to the correct lengths for your manifold, and linkages are fitted and adjusted for smooth operation. While initial linkage adjustment is done, final tuning is usually required once the engine is running.
• Sub-Assembled Kit: Each throttle body is precision factory assembled, but throttle shafts are left long for you to trim to suit your engine and manifold. Linkages are supplied for you to fit and adjust after trimming the shafts. This option is ideal for the experienced DIY builder who wants more control over the final fabrication.

Engine Management: The Brain of Your EFI System

While not typically included in the throttle body kits themselves, an Electronic Control Unit (ECU) is the indispensable brain of any EFI system. It processes inputs from various sensors (TPS, MAP, coolant temp, air temp, O2 sensor, etc.) and precisely controls fuel delivery (injector pulse width) and ignition timing. Selecting a programmable aftermarket ECU is essential for fully realising the benefits of your ITB conversion, allowing for custom tuning to match your engine's specifications and performance goals.

Cost Implications

Converting to EFI with an ITB setup is a significant investment. For illustrative purposes, a comprehensive 6-cylinder ITB kit might be priced around AUD $5,373.50 (inc GST for Australian customers) or AUD $4,885.00 (ex GST for international customers). This figure often excludes critical components like the TPS, fuel rail fittings, injectors, and the ECU itself, which would incur additional costs. Always enquire about the full scope of what's included and what's extra to avoid surprises.

Frequently Asked Questions

Can these kits be used on a 4-cylinder Datsun L20B?

The specific kits detailed here are designed for 6-cylinder L-series engines. While the principles and many components (like injectors, fuel rails, and general EFI hardware) are relevant, you would need to source a 4-cylinder specific ITB manifold and either two dual-barrel throttle bodies or four individual ones tailored for a 4-cylinder L-series engine. Always confirm compatibility with the supplier.

What is the benefit of 6° throttle plates?

Older throttle plates often used a 12° angle. When moved off the closed position, these caused a very large and sudden change in airflow, making smooth low-throttle driving difficult. 6° throttle plates provide a more linear and gradual airflow change, significantly improving off-idle and cruise drivability, making the vehicle much more enjoyable to drive.

Do I need an ECU for this conversion?

Yes, absolutely. An EFI conversion fundamentally requires an Engine Control Unit (ECU) to manage fuel delivery and ignition timing based on sensor inputs. The ITB kits provide the mechanical components for air and fuel delivery, but the ECU is the electronic brain that controls them. This is often the most complex and critical part of the entire conversion.

What kind of horsepower increase can I expect?

Horsepower and kilowatt ratings are guides only and vary significantly from engine to engine. Power output is influenced by numerous factors, including intake and exhaust design, cylinder head porting, camshaft profiles, compression ratio, fuel type, and the quality of the ECU tune. The listed HP figures for injectors are merely a guideline for naturally aspirated engines based on fuel flow, not a guarantee of total engine power.

What's the difference between a Fully Assembled and Sub-Assembled kit?

A Fully Assembled kit means the manufacturer has pre-cut throttle shafts, fitted linkages, and performed initial adjustments, aiming for a more 'plug-and-play' experience for the mechanical components. A Sub-Assembled kit leaves throttle shafts long and linkages unfitted, giving the builder more control over custom fitment and final assembly. The latter is often preferred by experienced DIY enthusiasts.

Why are there different injector sizes?

Different injector sizes (flow rates) are chosen to match the engine's power output. A higher horsepower engine requires more fuel, thus needing larger flow rate injectors. It's crucial to select injectors that can supply sufficient fuel for your target power level without exceeding their duty cycle, which can lead to lean conditions and engine damage.

The Road Ahead

Converting your Datsun L-series to EFI with an ITB setup is a rewarding project that revitalises your classic car. It's an investment in performance, efficiency, and modern drivability, transforming the driving experience. While the information provided here highlights kits for 6-cylinder L-series engines, the principles remain steadfast for any L-series variant. With careful planning, selection of quality components, and professional installation and tuning, your Datsun will be ready to tackle the road with renewed vigour and precision.

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