I figured since everyone usually up's their injectors, this would be good.
Configureing your BSFC:
When you want to upgrade injectors, you will need to know how much fuel you will need to supply the amount of horsepower you have or are shooting for. The BSFC is how many pounds of fuel it takes to make 1hp for 1 hour. The BSFC is usually around 0.45 for most street injection setups. So that means if you have a 400 HP engine with a BSFC of 0.45 you 180lbs of fuel per hour to maintain 400 horsepower. The formula for pounds per hour is :
BSFC x Peak HP = lbs/hr
For our example it would look like this:
0.45 x 400 = 180 lbs/hr
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Now if you had an 8 cyl. engine, each injector must supply 22.5 lbs/hr. Injectors will usually work best if they don't exceed 85% of their duty cycle. An injector that flows 26.5 lbs/hr will be at 85% duty cycle when it is flowing 22.5 lbs/hr. Sometimes, You may not find an injector that exactly matches what you need. In those cases, you should just move up to the next step wich in this case would be 30 lb/hr injectors.
The formula for injector sizing is:
lbs/hr = (BHP × BSFC) ÷ (No. of Injectors × DC)
Where:
BHP = Peak Brake Horsepower
BSFC = Brake Specific Fuel Consumption
DC = Injector Duty Cycle
If we have a engine with 300 hp, a 0.45 BFSC, 4 injectors, and we want a 80% duty cycle for the injectors, the formula would look like this:
lbs/hr = (300 × 0.45) ÷ (4 × 0.8) = 42.2 lbs/hr
You will want the injector that is closest to that size.
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Fuel Pressure
Most injectors are rated at 43.5 psi (which is about 3 bar). By changing the pressure, you change the flow rate. If you need 25 lbs/hr, and there is an injector that will flow 24 lbs/hr at 85% duty cycle, it is possible to use more fuel pressure to make the injectors flow more. It is better to do this when the injectors are just a little too small, than to go to larger injectors. The chart below will show what can be done by adjusting fuel pressure. You can see from the chart that there are quite a few options to get very close to what you'll need.
Rated Flow Fuel Pressure
@ 43.5 psi 40 45 50 55 60
19 lb/hr 18.21 19.32 20.37 21.36 22.31
22 lb/hr 21.09 22.37 23.58 24.73 25.83
24 lb/hr 23.01 24.41 25.73 26.98 28.18
30 lb/hr 28.76 30.51 32.16 33.73 35.23
36 lb/hr 34.52 36.61 38.59 40.47 42.27
55 lb/hr 52.74 55.94 58.96 61.84 64.59
83 lb/hr 79.59 84.41 88.98 93.32 97.47
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Using the following formula, You can see how much horsepower your injectors can handle.
HP = (lbs/hr × No. of injectors × DC) ÷ BSFC
Using a 0.45 BSFC is good for normally aspirated engines, but if blower, turbo, or dry nitrous system is being used, a 0.5 BSFC is better. These mods will usually run closer to a 0.5 BSFC. Remember that if you change fuel pressure, you must change the lbs/hr rating according to the chart. Lets say we want to know how much hp a set of injectors will support for a 4 cylinder turbo engine running at 85% duty cycle. The injectors flow 22 lbs/hr. The formula will look like this:
HP = (22 × 4 × 0.85) ÷ 0.5 = 150 hp
If you think the engine will exceed 150 hp, more fuel pressure or larger injectors will be required.
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Types of injectors
There are two basic types of injectors, saturated (high impedance) and peak and hold (low impedance). Saturated injectors are more common and draw less amperage form the ECU. Saturated injectors also create less heat because the have less amperage. A saturated injector will have an impedance of about 12 ohms, this means that at 12 volts it take 1 amp to hold the injector open. Peak and hold injectors will have an impedance closer to 2 ohms and draw about 6 amps. Most ECM's cannot handle the amperage and using peak and hold injectors will harm the them. If you desire peak and hold injectors a separate aftermarket injector controller or aftermarket ECM may be required. Peak and hold injectors use high current to open the injector very quickly and precisely, then they draw less to hold the injector open. For high horsepower and flow rates, the peak and hold injectors are much more precise, but they are more venerable because of the heat they make. If it is a street engine that will be daily driven, saturated injectors are more reliable for long term use. Peak and hold are better for high horse power and competition use.
Configureing your BSFC:
When you want to upgrade injectors, you will need to know how much fuel you will need to supply the amount of horsepower you have or are shooting for. The BSFC is how many pounds of fuel it takes to make 1hp for 1 hour. The BSFC is usually around 0.45 for most street injection setups. So that means if you have a 400 HP engine with a BSFC of 0.45 you 180lbs of fuel per hour to maintain 400 horsepower. The formula for pounds per hour is :
BSFC x Peak HP = lbs/hr
For our example it would look like this:
0.45 x 400 = 180 lbs/hr
----------------------------------------------------------------
Now if you had an 8 cyl. engine, each injector must supply 22.5 lbs/hr. Injectors will usually work best if they don't exceed 85% of their duty cycle. An injector that flows 26.5 lbs/hr will be at 85% duty cycle when it is flowing 22.5 lbs/hr. Sometimes, You may not find an injector that exactly matches what you need. In those cases, you should just move up to the next step wich in this case would be 30 lb/hr injectors.
The formula for injector sizing is:
lbs/hr = (BHP × BSFC) ÷ (No. of Injectors × DC)
Where:
BHP = Peak Brake Horsepower
BSFC = Brake Specific Fuel Consumption
DC = Injector Duty Cycle
If we have a engine with 300 hp, a 0.45 BFSC, 4 injectors, and we want a 80% duty cycle for the injectors, the formula would look like this:
lbs/hr = (300 × 0.45) ÷ (4 × 0.8) = 42.2 lbs/hr
You will want the injector that is closest to that size.
---------------------------------------------------------------
Fuel Pressure
Most injectors are rated at 43.5 psi (which is about 3 bar). By changing the pressure, you change the flow rate. If you need 25 lbs/hr, and there is an injector that will flow 24 lbs/hr at 85% duty cycle, it is possible to use more fuel pressure to make the injectors flow more. It is better to do this when the injectors are just a little too small, than to go to larger injectors. The chart below will show what can be done by adjusting fuel pressure. You can see from the chart that there are quite a few options to get very close to what you'll need.
Rated Flow Fuel Pressure
@ 43.5 psi 40 45 50 55 60
19 lb/hr 18.21 19.32 20.37 21.36 22.31
22 lb/hr 21.09 22.37 23.58 24.73 25.83
24 lb/hr 23.01 24.41 25.73 26.98 28.18
30 lb/hr 28.76 30.51 32.16 33.73 35.23
36 lb/hr 34.52 36.61 38.59 40.47 42.27
55 lb/hr 52.74 55.94 58.96 61.84 64.59
83 lb/hr 79.59 84.41 88.98 93.32 97.47
----------------------------------------------------------------------------
Using the following formula, You can see how much horsepower your injectors can handle.
HP = (lbs/hr × No. of injectors × DC) ÷ BSFC
Using a 0.45 BSFC is good for normally aspirated engines, but if blower, turbo, or dry nitrous system is being used, a 0.5 BSFC is better. These mods will usually run closer to a 0.5 BSFC. Remember that if you change fuel pressure, you must change the lbs/hr rating according to the chart. Lets say we want to know how much hp a set of injectors will support for a 4 cylinder turbo engine running at 85% duty cycle. The injectors flow 22 lbs/hr. The formula will look like this:
HP = (22 × 4 × 0.85) ÷ 0.5 = 150 hp
If you think the engine will exceed 150 hp, more fuel pressure or larger injectors will be required.
-------------------------------------------------------------------------------
Types of injectors
There are two basic types of injectors, saturated (high impedance) and peak and hold (low impedance). Saturated injectors are more common and draw less amperage form the ECU. Saturated injectors also create less heat because the have less amperage. A saturated injector will have an impedance of about 12 ohms, this means that at 12 volts it take 1 amp to hold the injector open. Peak and hold injectors will have an impedance closer to 2 ohms and draw about 6 amps. Most ECM's cannot handle the amperage and using peak and hold injectors will harm the them. If you desire peak and hold injectors a separate aftermarket injector controller or aftermarket ECM may be required. Peak and hold injectors use high current to open the injector very quickly and precisely, then they draw less to hold the injector open. For high horsepower and flow rates, the peak and hold injectors are much more precise, but they are more venerable because of the heat they make. If it is a street engine that will be daily driven, saturated injectors are more reliable for long term use. Peak and hold are better for high horse power and competition use.
