Fuel Injectors

Calculating Injector Size and Type

Static flow rates quoted are the result of testing at 43.5 PSI (3 Bar). Static flow is measured with the injector held open. Static flow rate tolerance is ± 3%.

The quantity of fuel delivered is controlled by the length of time the injector is open. This is referred to as pulse width.

Use the static flow numbers to calculate the maximum practical operating capacity. This number will be approximately 80% of the static flow. Flow rates may be increased by increasing the fuel pressure to a maximum of 73.5 PSI.

To determine fuel flow requirements, you should estimate the horsepower expected. In normally aspirated engines a Brake Specific Fuel Consumption (BSFC) of .5 lb. of pump gas, per horsepower, per hour or better can be expected. Taking the horsepower number and dividing it by 2 will give the fuel requirements of the engine e.g. a 300 HP engine will require 300 X .5 =150 lb. of fuel an hour, at maximum power.

Dividing the fuel requirements by the number of injectors, for this example we will use 4, we arrive at an injector capacity requirement of 150/4 = 37.5. Remembering that injector capacity quoted in the table, is static flow, we must now increase this number by multiplying it by 1.25 to allow the injector to operate at no more than 80% of its static flow. Therefore, 37.5 X 1.25 =46.875 lbs/hr. Consult the Injector Selection Table to find an injector with the right flow capacity.

Injector resistance is an important consideration when matching ECUs to injectors. Injectors are manufactured as low resistance or high resistance. Low resistance injectors typically measure in the 2 to 5 ohm range, high resistance being 12 to 16 ohms. It is important to match injectors with the injector drivers in the ECU being used. Generally speaking, original equipment ECUs are equipped with saturated drivers which drive high resistance injectors. Aftermarket ECUs are equipped with drivers for peak and hold injectors which are low resistance. Some aftermarket ECUs will drive both types of injector: It should be mentioned, however that injectors for saturated drivers do have a slower response time than those for peak and hold. Most peak and hold drivers will drive both high and low resistance injectors but, under no circumstances, should peak and hold injectors be driven with saturated drivers.

To calculate the current requirements of an injector use Ohms law and divide the system voltage by the resistance. Therefore, in the case of a high resistance injector of 12 ohms operating on a 12V system, 12/12 = 1 amp. In the case of a low resistance injector operating on a 12V system we have 12/2= 6 amps. Observe that the current requirement for a peak and hold injector during the opening phase of operation is much higher than the saturated type, the current peak being used to "snap" the injector open. Drivers for peak and hold injectors are typically limited to 4 amps or 2 amps for opening and 1 amp or .5 amps respectively, for the hold period.

Please view the Injector Selection Table


Available Products

Borla Part # TWM Part # Description Price Qty
206343 N/A Fuel Injectors
$90.64 Add to Cart
206054 2500-1030 Fuel Injectors
$88.00 Add to Cart
206385 N/A Fuel Injectors
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206390 N/A Fuel Injectors
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206388 N/A Fuel Injectors
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206051 2500-1021 Fuel Injectors
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206055 2500-1031 Fuel Injectors
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206068 2900-0030/A Fuel Injectors
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206482 N/A Fuel Injectors
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206508 N/A Fuel Injectors
$90.64 Add to Cart
206657 N/A Fuel Injectors
$88.00 Add to Cart