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Fuel Injector Spotters Guide and Information

So, how much power is this injector good for? That depends on the air/fuel ratio that is used, but a good rule of thumb is to divide this flow figure by 5 to get a hp capability. So, 322cc divided by 5 = 64hp maximum fuel flow with this injector. If you want to be pedantic, it's the mass of the fuel (not the volume) which is the critical factor. Assuming a "normal" fuel density, the mass of the fuel in pounds per hour can be worked out by Dividing the cc per minute figure by 10.5. For this injector, that gives a mass flow of 30.6 pounds/hour. To convert from pounds/hour to horsepower capability, multiply the figure by 2.04. So 30.6 pounds/hour multiplied by 2.04 gives a horsepower capability of 62.4hp - the same as we got from the cc/minute figure.

The power ratings discussed above are for each injector. This means that you need to multiply this rating by the number of injectors that are to be used. So, if you were using the Impulse RS 322cc injectors in a 4 cylinder engine (with one injector per cylinder) the max power that the injectors could deliver fuel for would be about 249.6hp. All of these figures are assuming that you are running an average fuel pressure of ~43psi and at 90% duty cycle.

  • 500cc per minute is approximately equal to 49lbs per hour which is equal to approximately 100hp.
  • lbs/hour = cc per minute / 10.5
  • lbs per hour = HP / 2.04
  • cc per minute = lbs per hour x 10.5
  • cc per minute = HP x 5
  • HP = cc per minute / 5
  • HP = lbs per hour x 2.04

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Vehicle Injector Types Factory Flow Rating Notes
1990-'93 Geo Storm GSi Peak and Hold 222cc
1990-'93 Geo Storm 2+2 & Stylus S Saturated 222cc
1990-'93 Isuzu Impulse & Stylus XS Peak and Hold 222cc
1991-'92 Isuzu Impulse RS AWD Peak and Hold 322cc
1988-'91 Civic Si/CRX Si Peak and Hold 240cc
1992-'95 Civic Saturated 240cc
1996-'00 Civic dx cx and lx Saturated 190cc
1996-'00 Civic ex/si Saturated 240cc
1990-'91 Integra RS/LS/GS Peak and Hold 240cc
1992-'00 Integra LS/GS Saturated 240cc
1992-'96 Prelude Non-VTEC Peak and Hold 240cc
2003-'07 Honda Accord 3.0 liter V6 Peak and Hold 240cc
1992-'96 Prelude VTEC Peak and Hold 345cc
1997-up Prelude VTEC H22 Saturated 280cc
1991-up Sentra SE-R/200SX SE-R Saturated 265cc
2002-up Subaru WRX Peak and Hold 380cc Baby Blue
2002-up Subaru WRX STI Peak and Hold 500cc Pink
1991-up MR2 Turbo Peak and Hold 440cc
Toyota MR2(non-turbo) 5SFE 2.2L engine Saturated 213cc
1987-'92 Supra Turbo Peak and Hold 440cc
1993-up Supra non-Turbo Saturated 315cc
1993-up Supra Twin-Turbo Peak and Hold 550cc
2000-up Celica GT-S Saturated 310cc
1990-up Miata 1.6-liter Saturated 215cc
1993-up Miata 1.8-liter Saturated 240cc
1984-85 RX-7 195500-0900 Peak and Hold 680cc Orange Top
1986-87 RX-7 195500-1350 Peak and Hold 460cc Red Top
1986-87 RX-7 195500-1370 Peak and Hold 550cc Tan Top
1988 RX-7 195500-1350 Saturated 460cc Purple Top
1988 RX-7 195500-1370 Saturated 550cc Purple Top
1989-91 RX-7 195500-2010 Saturated 460cc Red Top
1989-91 RX-7 195500-2020 Saturated 550cc Purple Top
1993-up RX-7 Twin-Turbo Saturated Primary 550cc Secondary 850cc
1990-'96 300ZX Twin-Turbo Saturated 370cc
1991-up 3000GT/Dodge Stealth non-turbo Saturated 210cc
1991-up 3000GT VR-4/ Dodge Stealth R/T TT Peak and Hold 360cc
1989-up Eclipse/Laser/Talon Turbo/non-turbo Peak and Hold 450cc Blue Top(95+ Black top)
390cc Tan top
240cc Orange/pink Top
210cc Light Tan Top
Mitsubishi EVO Peak and Hold 510cc Yellow Top (1-3)
560cc Red top (4+)
1986-89 Ford turboCoupe Peak and Hold 35lb/hr Brown Top
30lb/hr Green Top
Injector impedance describes the electrical resistance of the solenoid windings. These are usually grouped in two categories:
Low- 1.7 to 3.0 ohms (Peak and Hold Driver/Injectors) High- 10 to 16 ohms (Saturated Circuit Drivers/Injectors)
These type of injectors and drivers may also be called current sensing or current limiting. They are more expensive and complex than saturated circuit drivers, and are not generally used with domestic production ECUs. They are primarily used in aftermarket high performance systems. Most high flow injectors are low resistance (2-5 ohms) and use a peak and hold driver to activate them. The Peak current is the amount required to quickly jolt the injector open, and then the lower Hold current rating is used to keep it open for as long as the ECU commands. These require the extra kick from the higher current to keep the opening and closing time of the injector stable at the higher fuel flow rate. With this type of driver, 12 volts is still delivered to the injector, but due to the its low resistance, the current in the driver circuit is high. How high? Using Ohms's Law we can calculate the current rating (12v/2 ohms = 6 amps). This is substantial current flow and a Saturated Injector cannot handle it. The drivers also come in two values; 4 amp peak/1 amp hold, and 2 amp peak/0.5 amp hold.. Even though 6 amps may be available to operate the injector, the maximum it is allowed to reach is 2 or 4 amps, depending on the driver's current limit. Most domestic OE production EFI systems use an ECU with 12 volt Saturated Circuit drivers. These are very inexpensive, simple, and reliable. This type of driver works by supplying 12 volts to the injectors and the ECU turns it on and off to establish a fuel injector pulse. In general, if an injector has a high resistance specification (12-16 ohms) the ECU uses a 12 volt saturated circuit driver to control it. This means that the current flow in the driver and injector circuit stays low keeping the components nice and cool for long life. Conversely, a downfall of a Saturated Circuit driver is that it has a slower response time (and closing time) than a peak and hold type. This slower time can somewhat decrease the usable operating range of the injector energized by this driver. An injector operating on a saturated circuit driver typically has a reaction time of 2 milliseconds while a peak and hold driver typically responds in 1.5 ms.
There are some exceptions to this, notably the Bosch 803 injector used on the Porsche 944 turbo which is 4.7 ohms. Most manufacturers have used both types at one time or another. The trend lately is to use high impedance types in most production cars. The best way to determine impedance is to put a digital ohmmeter across the two electrical connections and see what it reads. The primary advantage of low impedance injectors is a shorter triggering time. When large injectors are fitted to high output engines, low impedance injectors will often give a better idle quality because of this fact. The primary advantage of high impedance injectors is the fact that less heat is generated in the drive circuit and often no external resistors are used.
Nozzle Types
There are essentially 3 different types of nozzles:


pintle injector

This is the most common type and still the best. A tapered needle sits on a tapered seat. When the solenoid is energized, the core and needle is pulled back, allowing the fuel to discharge. This design has been well proven for over 30 years.


Bosch disc injector
Bosch disc injector
Lucas disc injector
Lucas disc injector

The Bosch disc type uses the same type of actuation mechanism as the pintle type but replaces the pintle with a flat disc and a plate with tiny holes. These work fine with a good spray pattern but are slightly more prone to deposits plugging the holes. The Lucas type buries the disc up inside the body to reduce the mass of the assembly for quicker response. The Lucas types typically have a very narrow spray pattern which can affect idle and throttle response in some cases.


Rochester Ball injector

The Rochester