Please let me shed some light on the injector subject also, or should I say, let me turn on the lights for you. Injectors do in fact come with different internal resistance. (Impedance).   High resistance, called "Saturated", and low resistance, called "Peak and Hold", are the two types commonly used today. At this time,  - 90% - of all automobiles, including the Japanese, are using Saturated - 12 to 16 Ohm Injectors. Toyota uses Sat. injectors in all but the Turbo Models. Earlier models used a mix of the two.  The, electro-magnetic solenoid, fuel injectors used in all automobiles today are all grandchildren of the  Bendix company. Bendix is a subsidiary of the Chrysler Corp. and was the founder of the electronic fuel injection system that we use today. It was called  "The Electrojector" System and it was vacuum tube operated. Patent rights were reportedly sold to Bosch in the late fifties.   An interesting bit of trivia.

Injectors come in many different shapes and sizes also, -hose end, top/rail feed with both, American and Japanese size "o" rings, galley/side feed -and dual hose feed. Injectors are also manufactured with many different wire clip configurations, Type C,D(2types),E,F, 10 and an ever increasing number of Specialty Types. Toyota uses (c, d,e,f) to differentiate between P&H and Sat. Units. This is to prevent mix-ups in the service dept.  Type C & E are P&H and Type D&F are Sat.   Many of these injectors look exactly alike except for part #s.  Three types of top "O" rings are used and a multitude of lower cushions are in use. When changing injectors all of these problems must be addressed. Injectors should always be tested with a volt/ohm meter before using to determine type. Be careful, Injector types should never be mixed.  Sat. Injectors can be used in P&H systems, but not the other way around. More on this later.

Tomco does not make injectors, they sell Rochester, Lucas and Nippon-Denso brand, to name a few. The only injectors that they sell with plastic caps are Nippon -Denso  - Many early Toyotas used plastic pintle caps, along with most of the other Japanese cars in existence today. Bosch also uses plastic on 95% of its models. Lucas, no plastic pintle caps at all.  NOTE: all injectors use a molded plastic top. The Tomco part # for the 7M-GTE Injector is 15530 and guess what, -- its a Toyota/ OEM Nippon Denso, Made in Japan, injector.

SIZE / RATINGS ---- ALL INJECTOR MANUFACTURES USE CC PER./MIN. OR LBS. PER/HR. TO RATE AND CATALOGUE THEIR PARTS.  ---{CC /MIN. DIVIDED BY 10.50 = LBS. PER/HR.} This is the commonly used formula for pump gasoline, using a specific gravity of .73-. 74 and differs when temperature change and viscosity of the medium is altered.  Let me repeat, ALL manufacturers use the same basic method of sizing, regardless of Country of Origin, cc/Min. or Lbs./Hr.

Professional Racers always order injectors by the Static flow rate, (wide open) and will state System Pressure used.- (720cc @ 51 PSI) -- They calculate Brake Specific Fuel Consumption first and then use this formula.     (HP req. Per cylinder - X - B.S.F.C.) / Duty Cycle = Static injector flow rate required.  -----  (100 HP per. cyl.)  X  (B.S.F.C. of .55 lbs. fuel/HP /Hr)  =  (55 lbs./Hr or 577cc /Min) -divided by -.80 - (Duty Cycle) = 721cc /Min. This will be the required flow rate if running at @ 80% Duty Cycle.  This formula provides you with the required amount of fuel that each injector, at wide open, (100% Duty Cycle) will have to supply in order to support the target horsepower. System pressure used will determine the actual injector needed. This number only indicates the amount of fuel required, not the injector size. Some Drag Race cars, do in fact, run at 100% Duty Cycle. This is not an encouraged practice. A larger than necessary injector run at 70% duty cycle, will provide more controllable performance than an injector that is being pushed to 90%-95% limits.

TEST EQUIPMENT The available Injector testing equipment, on the market today consists of The New Age and the ASNU machines. Both of these machines are fine products and they perform as advertised. These units are designed with a capacity (Measuring device) of 100-cc per-tube, and only 90% of this is usable for testing. What this means is that these machines will only measure 90 cc /Min at full flow. At 80% Duty Cycle they are limited to 112 cc/Min. If you test a 550-cc injector in this machine it can only run for 9.8 Seconds without overflowing the test tube. As you can see testing at 60 Sec. will be 6 times more accurate than a 10-Sec. Test.  The Margin of error increases dramatically with a decrease in test time. If you use one of these machines you must test at very low speeds and for a very short period of time, you don't have any choice. In a test at 8000 rpm @ 80% Duty Cycle you would be limited to only 12 Sec. of test time, with a 550 cc Inj. I'm sure that these machines are quite adequate for most tune up applications and repair stations but they have their limits.  That limit is a, 6Ms at Fast Idle, test result. We don't feel that this is a very conclusive evaluation when testing high performance injectors. Time is money, but "In the Race for quality and perfection, there is no Finish Line," or Time Slip waiting for you.

All currently used injectors are designed to operate between 2.5 Bar/36.25 P.S.I.   and 3 Bar/43.5 P.S.I. Chrysler some times uses 3.7 Bar/55 P.S.I. as does Porsche. There are some rare exceptions to these standards, but they are rare. By using 3 Bar as a standard, we can easily compare an injector, rated at   252cc @ 2.5 Bar (36.25 P.S.I.), to an injector that is rated at 2.7 Bar, 3 Bar or 4 Bar.   (See Pressure  later)

Minimum cycle time for most pintle types is 2.0 Ms. for P&H and 2.5 for Saturated units. The Disc will cycle as low as 1.0 Ms., pulse width, in P&H and .2.0 Ms. for the Sat. Unit. (The Lucas Disc weighs only .4 Grams. and the Bosch / Nippon -Denso pintle is at 3.9 to 4 Grams. --- Ten times heavier) The reduced inertial loading of the disc, allows the Disc to overcome the hydro- static load at excitation quicker and return to it's seat faster, providing quicker response times and more consistent cycle-to-cycle values.

Most pintle type injectors fail at 86%/88% and the Disc will usually go to 92% +, depending on system pressure. All must cycle smoothly up to 85% to Pass. Bad injectors will sometimes go "static" at 70% or so and are discarded. NOTE: Most pintle injectors will increase flow rates up to 88%, 92% with Disc injectors, and then go "semi-static", half open-half closed, just before going full static. This time-out event occurs at different time/pulse width durations, in different injectors, but always produces a 50% or so Duty Cycle flow rate. This extremely dangerous situation will usually occur at the worst of times, full throttle-max boost-high RPM- just when you need 100% fuel delivery you get 50% and go dead lean.  BANG!!!  This problem seems to amplify a bit at higher pressures.

PRESSURE AND FLOW CHANGES Fuel pressure changes will alter flow rates as follows - To find a new Flow Rate from a PSI change, Divide the new Pressure by the rated or old pressure. Find the square root of this number and multiply it by the old or rated flow rate.  Example: Injector rated at 430 cc/Min at 43.5 PSI.  If you raise the pressure to 49 PSI - Divide (49 / 43.5) = 1.1264 --- The Sq.Root of 1.1264 = 1.0613 ---   Multiply 430cc X 1.0613 and you get 456.37cc/Min. This will be your new flow rate. The injector size will still be listed at 430cc/Min @ 43 PSI.

To find the Pressure required, to produce a Desired Flow Rate, use this Formula. Divide desired flow rate by test flow rate, Square this number, and multiply it by the test PSI. The answer is the PSI required to produce the desired flow rate. To increase a 720cc/Min. injector rated @ 43.5 PSI to 800 cc/Min. --(800cc per/Min) / (720cc per/Min.)= 1.111 X 1.111 = 1.234  (1.234  X 43.5 PSI)= 53.7 PSI.  New pressure of 53.7 PSI will yield 800cc/Min. from a 720cc/Min. rated injector.  Caution: Up-graded fuel pumps will be required in many cases when significant injectors or pressure changes are made.

PATTERNS Of the 6 Basic metering devices used today -- Pintle  (Bosch / Nippon -Denso type), Ball and socket (Rochester), Radius Rod  (Siemens), Swirl plate (some Mitsubishi), Diffuser/Pintle Type (Toyota - and some models of all makes) Air feed Atomizers (many makes for emissions reasons) and the Disc Type used exclusively by Lucas. The atomization and pattern width will increase on single discharge pintle type injectors at, higher pressures. The Lucas Disc type does not deviate as severely. Dual discharge, diffuser type, pintle injectors don't change atomization quality, at higher pressures, like the single pintle discharge injectors.  Dual discharge injectors target the fuel toward the valve stem and reduce wall wetting, (puddling) behind the valve. These injectors are not high atomizers but targeted delivery types.

The Lucas injector maintains its pattern, cycle to cycle, the best under varying pressures and pulse widths. Diffuser/Pintle injectors have a rather tight, wetter pattern (more coalescence) than single discharge injectors. This is evidently caused by the impact of fuel on the diffuser surface causing the fuel to partially recollect. This provides a more concentrated liquid volume flux at the center of the cone, a tighter pattern angle, and a more accurate targeting capability. Cross sectional area of the port and distance to the valve is crucial with this type of injector.

At 8000 RPM the intake valve is opening and closing at 66 times a sec. and is only open for an average of 9 Mil/Sec. At this cyclic rate the transient time to complete the delivery of fuel, from injector to valve, is critical. This is why; Indy car injectors are very precisely targeted and timed to provide a solid stream of fuel with non-existent atomization, LBDS, "Laser Beam Delivery System". In these engines the injectors can discharge fuel, at a "just prior to valve -open position", and get it all down the hole. As the fuel impinges the hot intake valve it virtually vaporizes and mixes quite well with the incoming air forming a very homogenous charge. This is one of the most extreme situations but it's a real interesting one. As an added benefit, the latent heat of fuel vaporized in the chamber also provides charge cooling that makes the mixture denser. A denser, heavier mixture (cold and thick) will produce more power then a thin (hot and light) charge. This is why Turbo intercoolers are so effective. Injector timing, phase angle, is altered by the ECU according to RPM in these systems and can control the delivery impact time precisely. In a, Steady State pressure, Fuel System the injector pulse is always moving at the same speed, regardless of engine speed changes. The velocity of discharged fuel is relevant to the area of the discharge port and the net operating pressure. Pressure changes activated by boost, at a 1:1 ratio, only compensate for port pressure and don't change the static pressure, flow rate or velocity. RPM adjusted fuel timing is utilized for this reason, it advances the injector timing based on engine speed, and maintains perfect impingement timing at all speeds.

 ATOMIZATION High atomizing injectors are usually used in Throttle body applications only, and have a rather wide spray pattern.  A wide, finely atomized pattern is wonderful for emissions and economy but can cause problems in higher performance engines. At low RPMs, with a low air flow rate, the slow moving finely atomized fuel has enough time to get past the valve and create a close to stoichiometric mixture. (Air/Fuel mixture of 14.70  - Chemically ideal)  As RPMs increase this mass can't keep up, with valve open time, and many of the fuel droplets impinge the port wall and condense. Atomized fuel can only travel at port "air speed" and in large quantities it can actually displace air in the port. With a highly atomized mix in the port, at intake valve opening, the lighter droplets of fuel will be partly blown back up the port. This is caused by the residual exhaust pressure still resident in the combustion chamber. Some of this reverted mixture will adhere to port walls and condense. This puddling fuel may find its way home, on the next intake cycle, but it will cause cycle-to-cycle air/fuel ratio variances. The higher inertia of the more condensed fuel will carry it to its target. "The liquid film that wets the walls represents a capacitance that greatly reduces the transient response of the engine." (SAE 950506) This problem is compounded in Gang fire and Semi-gang fire systems, but is not as troublesome in sequential fire systems. Gang fire systems fire all injectors, every rotation, at the same time, discharging half of the required fuel at each event. Semi-gang fire systems fire groups of injectors in the same fashion, half-and-half, each rotation. Sequential systems fire each injector at a pre-determined time and discharge all required fuel in one event, prior to intake valve opening. In either of the gang fire systems there is no timing-of-event technology in operation, and as you can see it's a rather simple system.  NOTE: 7M-GTE fuel systems are semi-gang fire, as is the ignition system, and the injectors are fired in the same order, 1&6-5&2-3&4, as the spark plugs. 2JZ/GTE systems are true sequential operations, 6 coils, 6 injectors, and 12 separate events---- A state of the art well formatted system.

 It's a known fact that you can't burn fuel until it's atomized. It's also known that you can't burn fuel without air. The most important, of all known facts is that you can't burn anything, if it's not in the combustion chamber. The secret is to provide adequately atomized fuel with as much air as possible.  Adequately atomized is the Secret Word of the day. Fuel does not have to be completely atomized at the injector tip (SMD of 10um - 20um) but it does have to get past the valve to do us any good. The more condensed the fuel delivery is the faster it will travel, (regulated by discharge area and pressure) and the more accurately it can be targeted. Resent (S.A.E.) "Injector Atomizing and Targeting" studies have provided us with one of the most prominent advances in High Performance Engine Management. These test programs have concluded that "accurate impingement onto the center of the valve head is vital for good vaporization" and "The targeting orientation of the injected fuel spray is a critical parameter in fuel evaporation" also that " Fuel injected directly onto the intake valve yields a significantly better engine response" (SAE950506) What all this means is, different engine designs require a different type of injector to operate efficiently and that 100% atomization is not always required or desired. In racing situations we usually have to do the best we can with what we have, or what's available. The goal, is of course, is to do the best in all cases, and in all situations. The best injector for your engine is the one that will yield an optimal fuel-air mixture and provide the required power output consistent with smooth and reliable operation.

INJECTOR TYPES:
Peak and hold injectors are fired at 4 to 6 Amps, through a ballast resistor, and then fold back to 1 - 2 Amps for the duration of the injection event. They are also known as "fold back" Injectors. Peak and hold injectors are faster responding than Saturated injectors by as much as 1 to 1.5 Ms. They are activated with more power at opening than the saturated types (4-6 Amps vs. .75 -1 Amp.). Peak and hold injectors will maintain injection delivery, cycle to cycle, continuity more accurately than the saturated type. This is particularly true and even more important in high-pressure  (75 - 100+ PSI) systems. The higher  Hydrostatic loading at excitation requires more amperage to initially activate the injector solenoid and properly maintain complete opening.   Peak and hold systems are more expensive to manufacture because they require one computer "injector driver" per injector in most applications. This is a design requirement in Sequential Fire Systems where each injector is fired at a very precise, pre determined, time in the 720 degree 4 stroke processes. P&H injectors are also wound with copper wire instead of brass wire.  Early 7M-GTE used Type E - P&H rail feed style up through 1992 and then changed to Type E, galley Feed units for the 2JZ/GTE Toyota lists and rates all of their injectors in cc/Per Minute at different pressures, 36.4 PSI.   &  41.2. PSI.---- 7M-GTE injectors are listed at 430 cc Per/Min. at 42.1 PSI. and the 2JZ/GTE are rated at 540 cc/Min.

Saturated injectors are used in almost all-standard production, 1998, engines because of the system cost and simplicity. Saturated based systems usually fire all injectors at the same time, once every rotation discharging half of the required fuel per cycle at each event. Some systems fire half of the injectors at one time and the other half at a different time. These systems are called "Batch Fire" and "Semi-Batch Fire " respectively.  This system is used in 90 % of all general production engines (cost and simplicity). In almost every case Manufactures will only use Peak and hold injectors in High Performance applications or in Turbo applications. This is true in the Ford/Mazda family, Chrysler/Mitsubishi family, Nissan Group and the Honda/Acura folks as of 1997. General Motors/Toyota cars are also in this same family. OEM APPLICATIONS GM uses Saturated Rochester injectors in everything but some of the High performance cars, hear they use Lucas Injectors, and in the turbo trucks they use Bosch.  Toyota uses saturated injectors in  everything but its turbo models - all Nippon-Denso. Honda, last year changed all but the NSX to saturated, most all of Keihin make with some IPT. Nissan uses saturated units only, as of this year, Jecs or Hitachi manufactures. Chrysler/Mitsubishi  -  same deal - all but the turbos are saturated, Siemens or Bendix make. Ford uses Bosch or Nippon-Denso depending on the Model. All are Sat. except Turbo Models. Bosch and Lucas injectors are used in VWs.. BMW , Bosch up until this year,   now Lucas ---  European cars use an assortment of injectors including Weber, Bosch and Lucas.