Everything you need to know about injectors for your turbo Bimmer

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  1. Everything you need to know about injectors for your turbo Bimmer 
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    This article is by a writer at Precision Turbo...
    but applies to any make of injectors

    Precision injectors have fueled everything from daily drivers to today’s quickest and fastest race vehicles. These highly precise injectors range in domestic sizes range from 24 lbs/hr to 165 lbs/hr or 240cc to 1,600cc in high & low impedance configurations with a variety of nozzle styles. Flow matched and hand selected for optimal performance, Precision injectors are what you need for a wide variety of Domestic and Sport Compact engine applications.

    Precision offers a variety of injectors to suit your needs. Many injectors utilize ball on cone sealing to for the most accurate fuel delivery possible. Test results have proven accurate metering in extreme conditions and underhood operating temperature ranges. Metering is controlled by a 6-hole orifice just below the valve which merges the fuel streams into finely atomized spray cone for improved starting and improved hot fuel handling. Each injector also contains an internal filter for increased protection against harmful fuel contaminants. Most Precision injectors are compatible with alcohol fuels and have low noise operation.

    Fuel injectors provided through Precision go through a battery of tests to ensure accurate fuel delivery and reliability. Functional measurements that Precision audits include open/closing time, coil inductance, coil resistance, external leakage, static & dynamic minimum operating voltage, linear & dynamic flow, insulation resistance, response time, repeatability, slope & offset, impedance and voltage offset.

    Injector Basics
    Unlike mechanical fuel injectors which run open constantly, electronic fuel injectors use timed delivery techniques by rapidly opening and closing. When injectors open, fuel pressure forces fuel through a tiny orifice and into the airflow coming through the intake runner. This action causes the fuel to break down into smaller droplets or a mist which is then carried to the combustion chamber. The amount of flow from an injector is determined by fuel pressure, nozzle size and duty cycle. Cleanliness of the injector tip can also affect the amount of flow, since a clogged injector can impede the delivery of fuel.

    Duty Cycle
    How much fuel is delivered is controlled not only by fuel pressure, but also by how long the injector is energized by the driver circuit in the vehicle’s ECU. This commonly referred to as duty cycle.

    Injectors that pulse or open and close rapidly are measured in terms of milliseconds and have a variable duty cycle. Flow ratings for injectors are usually measured when they are in a static condition, which means they are held open continuously. This is referred to as a 100% duty cycle. In high performance applications, most injectors operate best when they are run at a 70 to 90% duty cycle, which means they flow 70 to 90% of the static flow rating. Operating an injector within this range helps reduce the build up of heat within the windings of the injector, which can lead to premature failure.

    Fuel Pressure

    The volume of fuel delivered also depends on the amount of pressure within the fuel delivery system. Lower pressure causes less fuel to be delivered while higher pressure results in more fuel delivery. The advertised static flow rates are tested at a fuel pressure of 43.5 psi or 3 Bar.

    Users should also remember that the use of larger injectors can also stretch the limits of a fuel delivery system. Always match the size of the fuel pump, line size and rail to the size and number of injectors installed. Contact Precision Turbo for information and best pricing on sizing your fuel delivery system correctly.

    Electrical Actuation
    Since a vehicle’s ECM is the driving force behind the operation of an injector, matching injector impedance to the driver circuits within that engine management system is important. Mis-matching driver circuits with injectors can affect the reliability of the ECM and injector timing at high rpm ranges.

    Injectors can also be categorized by their resistance to the electromagnetic force which opens the coil contained within the body. This resistance is also known as impedance and is measured in ohms. High impedance injectors are rated at 12 to 16 ohms while low impedance injectors usually have a resistance of 2 to 5 ohms.

    Driver circuits are usually characterized as being either saturation or peak & hold, depending on how they operate. Saturation drivers are commonly found on OEM production vehicles because of their low cost and simplicity. These drivers use relatively low amounts of current and generate less heat, but also have a slower response time.

    Peak and hold (also known as current sensing or current limiting) drivers are used more commonly on high flow, low impedance injectors and use a burst of power to open the injector quickly and then reduce the current to hold it open until the metering event is finished. Most peak and hold drivers will operate injectors of any impedance, but high flow, low impedance injectors should never be used with high impedance, saturated drivers.
    Last edited by Boostist; 18-06-2007 at 23:04.
     
     

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    Part 2 of the same article:

    Nozzle Designs
    Fuel injectors use a variety of nozzle designs which affect the spray pattern. Pintle style nozzles use an annular orifice to produce a conical spray pattern. Multi-hole designs use precisely spaced and aligned orifices to deliver a cone shaped spray pattern also.

    Pencil or single hole nozzle styles are used to shoot a narrow stream of fuel at a targeted area. Disc style injectors use a drilled disc that moves with a spray pattern similar to pencil injectors.

    While each design has its own advantages, it's generally accepted that disc metering is quicker to respond and more resistant to clogging. Some multiple hole designs use a ball and seat design to seal the orifice. This design tends to offer longer service life with a wider spray pattern and increased fuel delivery at the price of a slightly slower response time. Pintle designs tend to react slower and have a shorter service life. When upgrading to larger injectors, most industry experts recommend a ball and seat design as offering the best combination of features and benefits.

    Spray Patterns
    There are several basic spray patterns used in automotive fuel injectors. Pencil streams use a constant flow with a narrow angle of distribution. Split pencil designs use multiple streams and are commonly found in multi-valve applications. Bent or oblong spray patterns are used when the spray target is not in direct line with the injector nozzle tip. Conical spray patterns are more typical with performance injectors and use a cone shaped geometrical pattern.

    There are many theories about what kind of spray pattern is better and why. While much of that depends on whether throttle body, port or direct fuel injection is utilized, there is much research still going on in this field of study. Spray patterns can be easily viewed on a test stand, but those patterns are often distorted under actual operating conditions especially in the case of forced induction engine applications. Some of the nation's leading universities and research labs are using Phase Doppler Particle Analyzers, electron microscopy and synchrotron X-ray beams in order to gain greater insight into spray distribution, atomization and burn efficiency within the combustion chamber to increase performance and reduce emissions. Even so, spray patterns aren't as critical in many race applications since meeting emissions is not an issue.

    Sizing Injectors
    While there are many different types and styles of injectors on the market today, it's important to note that all manufacturers use the same basic method of sizing, regardless of country of origin. Domestic injectors usually measure fuel flow in terms of pounds per hour (lbs/hr) while international applications measure in cubic centimeter (cc's).

    A simple way to figure what size injector you need is to divide an engine's peak horsepower at the flywheel by the number of injectors. That number should then be multiplied by the Brake Specific Fuel Consumption (BSFC). For a naturally aspirated engine, this number is typically. 50 After you've finished multiplying, divide that by a Duty Cycle of .80. The formula looks like this:

    HP / Number of Injectors x BSFC / Duty Cycle

    Here's an example for an eight cylinder engine that we found would need a 24 lb/hr injector:

    300 HP / 8 = 37.5 --> 37.5 X .50 BSFC = 18.75 --> 18.75 / .80 Duty Cycle = 23.43

    To convert lbs/hr to cc's, multiply by 10.2. To convert cc's to lbs/hr, divide by 10.2.

    Readers should note, however, what Brake Specific Fuel Consumption factor is in order to use the above formula correctly. A BSFC of .50 means an engine will use .50lbs of fuel per hour for each horsepower it produces. Competition engines with high volumetric efficiency should use a BSFC of .45 while forced induction engines should use a figure of .65.

    For our readers ease, we have done all the math for you and determined a horsepower rating per injector as shown on the tables below. Simply multiply the listed rating by the number of injectors to determine if these will support the peak horsepower for your engine.

    Domestic Injectors >Each Inj.
    P/N Size lb/hr Impedance Nozzle Supports
    DMI24 24 High Pintle 43 HP
    DMI30 30 High Disc 54 HP
    DMI37 37 High Ball 67 HP
    DMI38 38 High Disc 68 HP
    DMI42 42.5 High Disc 77 HP
    DMI50 52 High Ball 94 HP
    DMI55 55 Low Ball 99 HP
    DMI65 65 Low Ball 117 HP
    DMI75 75 Low Ball 135 HP
    DMI84 84 Low Ball 151 HP
    DMI95 95 Low Ball 171 HP
    DMI165 165 Low Pintle 297 HP


    Sport Compact Injectors Each Inj.
    Size Nozzle >Supports
    P/N CC Impedance Type 90% D.C.)
    SCIO310 310 High Disc 52 HP
    SCIO400 400 High Ball & Seat 68 HP
    SCIO440 440 High Disc 77 HP
    SCIO525 525 High Ball & Seat 90 HP
    SCIO580 580 Low Ball & Seat 100 HP
    SCIO680 680 Low Ball & Seat 117 HP
    SCIO780 780 Low Ball & Seat 135 HP
    SCIO880 880 Low Ball & Seat 151 HP
    SCIO1000 1000 Low Ball & Seat 171 HP
    SCIO1600 1600 Low Ball & Seat 275 HP


    Injector Connections
    Injectors can mounted to the fuel rail in any number of different ways. Top feed injectors use a rigid fuel rail to press the injector into the injector bung on the manifold and seal the O-rings. All Precision brand injectors for domestic applications are a top feed style and use a 14mm round O-ring to seal against fuel leaks.

    Precision also manufactures top feed replacement injectors for popular Sport Compact applications such as Honda and Mitsubishi. While these may not fit every application, stock fuel rails are typically replaced in favor of high flow rails which will work with these upgraded injectors.

    Electrical connections can be broken down into two basic types. The most common today is the L-Jet connector which provides a weatherproof seal. Older applications use a D-Jet style connector. Some manufacturers such as Subaru and Toyota use their own style of electrical connector which is not compatible with either of the above.
    Last edited by Boostist; 18-06-2007 at 23:05.
     
     

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    excellent. Looks like I need 1000cc Low Impedence for my project then
     
     

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    Quote Originally Posted by edler View Post
    excellent. Looks like I need 1000cc Low Impedence for my project then
    be carefull with those things

    not only is it nearly impossible to get anything to idle with them, but you can easily fuel was your cylinders and hurt your engine

    if you need that much fuel you should consider some kind of staged injection setup otherwise your gonna have horrible driveability and a real hard time trying to control those monsters

    i run a set of 1000's in my car and trust me it was a nightmare to get em to work
     
     

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    Quote Originally Posted by topshotta02 View Post
    be carefull with those things

    not only is it nearly impossible to get anything to idle with them, but you can easily fuel was your cylinders and hurt your engine

    if you need that much fuel you should consider some kind of staged injection setup otherwise your gonna have horrible driveability and a real hard time trying to control those monsters

    i run a set of 1000's in my car and trust me it was a nightmare to get em to work
    How do some supras happily run 1600 low impedence injectors then?
     
     

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    they idle at over 1000rpm with a/f ratios in the 10's

    i tuned a mitsu 4G63 with 720's and at minimal duty cycle of about 1.19ms the a/f was at 11.2

    in my S50B30 with the 1000's my idle is at 1000rpm with a/f's in the mid 11's as well, only due to reduced fuel pressure at idle
    i dont mind it since it quiets down the chatter from lightweight flywheel
    but theres almost no way of leaning it out anymore of the injectors simply wont open

    hmmm... maybe i need a roots blower as well as the turbo
    instant boost and leaner idle
    i can kill 2 bird with one stone
    gotta think about this one.........

    there are always sacrifices to be made when making big HP numbers
    when a vehicle necessitates the use of such large injectors idle is always the first problem
     
     

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    Quote Originally Posted by topshotta02 View Post
    they idle at over 1000rpm with a/f ratios in the 10's

    i tuned a mitsu 4G63 with 720's and at minimal duty cycle of about 1.19ms the a/f was at 11.2

    in my S50B30 with the 1000's my idle is at 1000rpm with a/f's in the mid 11's as well, only due to reduced fuel pressure at idle
    i dont mind it since it quiets down the chatter from lightweight flywheel
    but theres almost no way of leaning it out anymore of the injectors simply wont open

    hmmm... maybe i need a roots blower as well as the turbo
    instant boost and leaner idle
    i can kill 2 bird with one stone
    gotta think about this one.........

    there are always sacrifices to be made when making big HP numbers
    when a vehicle necessitates the use of such large injectors idle is always the first problem

    but who gives a damn if it idles rich??

    800-1600cc ~ as you say are always going to have idling problems but who cares?

    1000 rpm is fine and you mucho fuelo at your disposal for when you hit full boost :

    If your talking about for a daily driver, then it 'may' be a problem? but Ive got some 1000 cc injectors to go on my engine build and idle is the least of my concerns

    main one is are they big enough for my requirements :

    PT76 GTQ + S50 B30 = fun
     
     

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    yea see mine is a daily driver

    i think they should be big enough but that all depends on how much boost you plan on running
     
     

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    Quote Originally Posted by topshotta02 View Post
    yea see mine is a daily driver

    i think they should be big enough but that all depends on how much boost you plan on running
    Hehe

    Well, Ive sold them and have some 1600cc RCs on the way from the good ole US of A

    Id rather have too much fuel than too little..and I plan to run at least 25psi minimum up to 35psi plus :

    I worked out using a few injector calcs that they would cover it but have quite high duty cycle.

    In for a penny, in for a pound and all that!
     
     

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    once tuned what is the average bsfc of a turbo car? Can it be fine tuned to .55 or lower?
    98 European E36 M3 (SMG) Blue, Weichers Strut Tower bars, H&R sway bar kit, custom exhaust, Stoptech ST-40 332mm pagid blue and yellow's on track, SaBelt 6 point belts, KW Club Sport 12kg/mm F&R. Motec M600 with cam control option for Dual Vanos. Turbo build after n/a tune is complete and vanos control is mastered.

    http://www.underpressuregarage.com
     
     

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