This is a diagrammatic representation of a typical 4-cylinder installation where we assume that two of our 2900 series throttles have been installed on a suitable manifold and the injectors are mounted in the throttle bodies.


(a) Except when mounted in the fuel tank, fuel pumps should always be mounted below the level of the fuel.

(b) Calculate the fuel flow requirements of the engine, by estimating BHP and BSFC (brake specific fuel consumption, usually shown in pounds of fuel consumed, per horsepower/ per hour). This will provide a guide as to how much fuel pump capacity you will need.

(c) Capacity of the fuel rail is important to provide adequate volume of fuel for rapid acceleration and to provide damping of transitory pulses cause by the opening and closing of the injectors.

(d) Borla Induction fuel pressure regulators should always be installed downstream of the injectors.

Carbs vs Fuel Injection
Carbs vs FI
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Basically, an electronic fuel injection system (EFI) works by delivering high pressure fuel to an electrically operated valve called an injector. Where the electronic wizardry comes in, is delivering the right amount of fuel, at precisely the right time for every engine operating condition, across the rev range.

The electronic control unit (ECU) receives information from a variety of sensors, in and around the engine and makes the appropriate adjustments to fuel delivery to maintain perfect, preset air/fuel ratios.


The problem with original equipment EFI is that reprogramming for nonstandard applications involved creating a new chip for the ECU, a process beyond the capabilities of most engine tuners. Even if a modified chip was available commercially, it was still not possible to “tune” the injection system for further engine modifications. In the late 1980s a number of programmable aftermarket injection system ECUs arrived in the US, such as those manufactured by 034EFI, AEM, DFI (Accel), Electromotive, Felpro (FAST), Haltech, Hondata, Link, MoTeC, OnTronic 32-bit Fuel Injection, SDS, Split Second, and Wolf. These systems can be programmed “on line” by connecting them to an IBM-type personal computer. They allow the tuner access to the fuel maps for idle, transition, wide open throttle, cold start, turbo boost enrichment, and in some cases, ignition timing.

Tim Suddard, owner and editor of Grassroots Motorsport Magazine, writing in an article about EFI states the following major advantages:

  • The extreme accuracy of fuel delivery by the ECU, at any load or RPM, provides the engine with air/fuel mixtures that fall within a tiny window of accuracy required for maximum power, or maximum economy.
  • EFI systems are not subject to the usual fuel surge and frothing associated with floats and float bowls in carburetors. One of the limiting factors in race car lap times has been the ability of the fuel system to deal with G forces. Gravitational forces in both horizontal and vertical planes have no effect on EFI systems.
  • ECU control of air/fuel ratios allows racing engines to safely operate nearer to the “ragged edge”.
  • PC programmable EFI can easily be adapted to suit future engine modifications as a vehicle evolves. Adjustments to fuel and ignition curves being as simple as making a few keystrokes on a PC.
  • EFI generally permits greater flexibility of intake manifolds designed to achieve higher inlet air flow rates and consistent cylinder to cylinder air/fuel distribution.
  • More efficient, higher compression ratios are usable, due to accurate fuel metering. This is especially the case with EFI units incorporating ignition control.
  • When converting to forced induction, turbocharging, or supercharging, EFI will enable the user to program boost-relative enrichment easily, usually leading to substantial power increases as a result of accurate fuel delivery.
  • Most EFI systems compensate automatically for changes in altitude and ambient temperature. Calibrating a fuel system for a specific race venue is hardly necessary with EFI, if adjustments are to be made, a few keystrokes on a PC are all that is necessary.
  • Some EFI systems also have a provision for a cockpit-mounted mixture control with which the driver can vary the air/fuel ratio. Borla Induction's FAST Air/Fuel Meter is particularly useful for this purpose, providing a visual, onboard read out of the air/fuel ratio with its 30 LED display.
  • The solid state electronics in EFI systems are not susceptible to the mechanical failures associated with carburetors. Tuning parameters remain as programmed, with never any need to adjust for wear.

TWM was a manufacturer of intake manifolds, for competition style carburetors, such as the Weber DCOE Series. When a number of programmable, fuel injection electronic control units (ECUs) became available in the performance aftermarket, it was obvious that many enthusiasts would want to convert from carburetors to injection. TWM throttle bodies permit the conversion of virtually any engine equipped with a suitable manifold to fuel injection. These individual runner systems are the best way to convert a competition engine to EFI.

The DCO and DCOE Series Webers, the PHH Series Mikunis, the ADDHE Series Solex, the SK Racing sidedraft, the IDA (2 and 3 bbl) IDF and DCNF Series Webers, and DRLA Dellortos.

Yes, TWM manufactures several dedicated injection manifolds to convert engines to individual runner EFI for racing purposes. We also make the 2000 Series throttle bodies which are dedicated injection manifolds for Honda, Ford, VW, and others. TWM also produces some large bore single barrel units which have many applications and several throttle bodies for upgrading original equipment EFI systems including the “Big Throat” throttle bodies for Datsun Z cars.

Generally speaking, no. All these systems are designed for aftermarket ECUs, such as those manufactured by Hondata.

Carburetors rely on the pressure differential created by a venturi to draw fuel from the float bowl via the various jets and circuits. By their very nature these components cause a restriction to air flow, and contribute to pumping losses. The inevitable disadvantage of this system is that, while a venturi of a certain size may be necessary to provide low speed driveability it then acts as a restriction at high RPM. Because the fuel in an EFI system is injected under high pressure there is no need for any venturi. That is the reason throttle bodies flow so much more air than a carburetor of the same size and the reason that EFI systems can use larger throttles than the equivalent carburetors.

Original equipment EFI systems are configured to meet very stringent emission regulations and to provide "soft" driveability characteristics. Positioning the injector as close to the inlet valve is beneficial in this respect. Maximum power however, is usually obtained by moving the injector away from the inlet valve, some racing engine manufacturers going as far as to mount the injector high in the velocity stack and others installing two injectors, designed to operate at different RPM. When Borla Induction designed the throttle bodies our engineers were not in favor of having high pressure fuel on the atmosphere side of the throttle plate, although this could have resulted in some power increase. We compromised by mounting the injector as far from the cylinder head as possible while still maintaining the safety afforded by keeping the fuel downstream of the butterfly.

You will need a suitable manifold, throttle bodies to suit your application, a fuel rail kit, a high pressure fuel pump, a filter and a regulator, appropriately sized injectors, a return line to the fuel tank or fuel cell and an aftermarket ECU. Most EFI kits are supplied with wiring harness, sensors and throttle position sensor.

View a diagram of a typical Fuel Injection installation.