FUEL INJECTION V. CARBURETION, AN OVERVIEW:
Carburetors, no matter how sophisticated are riddled with compromises. Sized for maximue horsepower they lose low speed driveability and midrange torque. Booster Venturis, constant velocity slides, and spray bars all hinder the free passage of air and render the airflow dirty. Fuel Injection offers increased sophistication through the use of fast acting electronics and preprogracmed functions to give your engine the lightning fast response and driveability that carburetors cannot match. Electronic control of cold start, warm-up cycles, accelerator pump functions and altitude or barometric corrections are but a few of the advantages of digital electronic fuel injection. The biggest or most immediate advantage is in the area of driveability. There is no need for choke levers or long ware-ups, no slipping of the clutch to get your race carbs off the line, and no need to rejet for atmospheric or altitude changes. Electronics give a much more precise control over fuel delivery than any mechanical device can. Better control means more power and much quicker throttle response. Once you have experienced the accuracy and precision of fuel injection you will never go back to carburetion.
Electronic Fuel Injection can be broken down into three types: (1) Pure speed density
systems; (2) Mass flow sensing systems; and (3) Closed loop oxygen sensing in either mass
flow sensing or digital speed density format.
Of the three, pure speed density systems are the Simplest. These designs are preprogrammed to a set of RPM, load and throttle angle (H-Alpha) values which totally control fuel delivery. If you change cams, bore, stroke, or even exhaust systems the calibration is out the window as these systems are noncorrecting. You must reprogram with a computer or attempt gross movements with screw type potentiometers to set your calibrations. If you have read of theWeber-Marelli system on the factory Ducatis you are well aware of these systems problems. If you are right on they work fine, but differing conditions or mechanical changes render them useless.
Mass Flow Sensing systems are extremely accurate, delivering fuel according to actual air consumed. Bosch LE Jetronics (Flapper-Valve) as installed on BMW K75 and K100s are of this type. Although they are accurate and reliable, these designs severely limit airflow and are very slow responding. high performance was not a consideration in their design. A second type of mass flow sensing is either hot wire or hot film designs which use heated elements to measure input air mass. They are not suitable for high performance use for three reasons:
(1) They are subject to false output signals due to pulsations in the inlet tract which provide unwanted cooling events to the hot sensor element.
(2) Mass flow meters cannot be located near the inlet valve or turbocharger impellers thus they require a lengthy inlet tract with a single-point restrictive entry. This precludes the use of individual velocity stacks.
(3) Mass flow systems were conceived as accurate emissions controls, not high performance systems.
By far the best high performance design is the RSR variation... The Closed-Loop Speed Density Design. This design eliminates restrictive flapper valves and hot wire flow meters allowing individual velocity stack inlet tracts. The preprogrammed speed density design allows you complete freedom to program all variables but due to its closed-loop oxygen sensing capability it automatically corrects and adapts to changes to cams, displacements and exhaust systems. The oxygen sensor is preprogrammed to enter the driving cycle at precise points and will automatically adjust your fuel base map memory. This means that the RSR system actually has an infinitely variable, ever-changing, three dimensional fuel delivery curve instead of a single preprogrammed set of values.
EXCLUSIVE FEATURES OF THE RSR SYSTEM
ELECTRICAL CONNECTORS - All connectors are triple silicone seal waterproof connectors -
These parts will withstand the most severe abuse.
WIRING - The heaviest gauge practical wiring is used to minimize resistance losses and to provide the maximum fatigue resistance. SENSORS - All sensors are Automotive O.E.M. quality.
1. Throttle Position Sensor (T.P.S.)
2. Air Temperature
3. Oil/Water Temperature
4. Manifold Absolute Pressure Sensor (M,A.P.)
5. Idle Air Control Motor (I.A.C.)
6. Oxygen Sensor
Should you have a sensor failure, these parts are available at any auto parts store, General Motors dealer or AC-DELCO outlet in the world.
INJECTORS - Bosch exclusively - The best in the world. We use eight injectors on inline fours to cover the fuel requirements of the most highly modified normally aspirated and turbo motors.
FUEL PUMP - The best and most reliable fuel injector pumps in the world. Fuel delivery adequate for 300 to 450 hp depending on the intended application.
PRESSURE REGULATOR - Bosch - preset to regulate fuel pressure for your application. Preset in all applications for 51 psi at zero inches of vacuum .
FUEL RAILS - Fuel rails are actually fuel reservoirs or accumulators. Therefore, all RSR designs pass fuel past the injectors in a large capacity rail and never dead-head the fuel off of a 'T' at the injector. By flowing fuel past the injector we also help cool the injector and the fuel. Designs which dead-head fuel at the injector are subject to heat soak and vapor lock.
ECU - Electronic Control Unit - To do your own calibrations you can use any IBM PC or compatible with RSR software and User Interface to set all ECU values with an extremely powerful AUTOCAL calibration software program. Instead of changing brass jets and getting soaked with gasoline you just tap computer keys. The program is written in conversational English but a basic knowledge of IBM MS DOS is required.
SOPHISTICATED DATA LOGGING - The RSR fuel injection ECU also functions as a data logger. You can preprogram your ECU to record engine operating conditions and either download this data to an external printer or read the data or manipulate it from the files created. This feature alone is worth as much as a $2,500.00 to $20,000.00 racing data logger from RACEPACK or CRANFIELD.
The one criticism is that insofar as digital control is concerned that closed loop systems are too slow reacting for high performance'. While this may be true of some O.E.M. systems it is by no stretch of the imagination true for the RSR digital closed loop design. We have total control of our closed loop oxygen sensing (Lambda) functions. The RSR system can be totally programmed in the following areas:
1. To act as closed loop (oxygen sensing) or open loop (pure speed density) system.
2. To choose the rpm at which the system enters and leaves the closed loop mode.
3. To choose the engine operating temperature at which the system enters the closed loop mode.
4. To determine the percent of throttle opening at which the system leaves the closed loop mode (typically 50%)
5. To determine under which load or acceleration conditions the system will exit closed loop.
6. To reset the target point for closed-loop operation i.e., cause it to run richer or leaner than the normal 14.7 to 1 air/fuel ratio (stoichiometry).
As you can see the RSR system is quite complex in its approach to closed loop operation. Its ability to run open loop at idle and low rpm allows you to install longer duration cams which admit too much free oxygen and confuse the 0-Sensor in these ranges. If you are running leaded racing gas you cannot run a closed-loop system as the lead will foul the oxygen sensor. In this case you can simply program the ECU to run in the open loop mode and plug off the oxygen sensor port. The benefit of closed loop operation however is the systems ability to constantly adjust itself to maintain a stoichiometric fuel ratio of 14.7:1. The RSR system can automatically modify the base map figures over 50% to insure this air/fuel ratio is maintained. This ability of the system to program itself in closed-loop operation means that it will automatically adapt itself to changes in cams, exhaust systems and even displacement changes.
TECHNICAL DESCRIPTION OF RSR SYSTEM COMPONENTS
1. Electronic Control Unit (ECU). The RSR ECU is powered by the vehicle's 12 volt system. The unit is contained in an aluminum anodized and hermetically sealed rectangular structure that measures 5 x 5' X 1.2'. The ECU is connected to the fuel injection wiring harness by a quick detach 23 pin connector which receives signals from the various sensors. The ECU also has a three pin connector for the IBM PC/Compatible software interface using the RSR AUTOCAL Calibration Software. The ECU contains the instructions or programming which controls the electronic fuel injection. These instructions cannot be 'lost' if you lose battery voltage or disconnect the unit. The ECU is protected against high voltage inputs and is really only susceptible to damage if operated, as with most electronics, at extremely high temperatures. The ECU should not be mounted in direct proximity to engine or exhaust heat. Temperatures should not exceed a maximum 150 degrees Fahrenheit. Typically the ECU is mounted as far away from engine heat as possible. On a motorcycle the ECU is normally mounted in the tail section or under the seat . The ECU receives inputs from sensors which measure manifold pressure, coolant temperature, air temperature, throttle position, engine rpm and battery voltage. In addition to these parameters the RSR ECU also measures the oxygen content in the exhaust system with a Bosch Lambda sensor. This device is designed to provide real-time feedback allowing the ECU to constantly tailor the programmed instructions so that the air/fuel mixture is maintained at a constant 14.7 to one ratio. Stoichiometry or 14.7 to one is the chemically correct point at which the most complete burn or combustion takes place. By operating in the oxygen sensing or closed loop mode the optimum in economy and general driveability will be achieved. The ECU also controls the engine's idle speed both during warm-up and normal operation as well as air by-pass during closed throttle deceleration. The ability of the ECU to control air bypass through the idle air control motor gives the RSR system complete predictability under all conditions with no need to have separate choke mechanisms or air bleed screws. The RSR ECU is a true microprocessor based system which has extensive RAM and ROM memory capabilities to handle up to 8 injectors operating as high as 16,000 rpm. Other fuel injection systems which do not offer closed loop control of both idle as well as mixture strength are little better than 'electric carburetors'. The RSR system is a truly sophisticated fuel delivery system that is more akin to an OEM automotive system in terms of the advanced electronics, programming and material construction.
2. Fuel Pump. The RSR system uses specially designed pumps capable of delivering enough fuel for 450 horsepower. Typical automotive fuel pumps are not designed for fuel injection purposes. Even a high output pump like a Blue Holley race pump which is rated at 90 plus gallons per hour cannot generate enough pressure to be used with fuel injection. The Holley pump may be capable of generating 9 psi but a fuel injection system with an initial 51 psi of line pressure will have to deliver 71 psi of pressure under 20 pounds of boost with a racing turbocharger set up. RSR uses either roller style or gerotor style fuel injection pumps depending on the final application. Depending on their requirements our pumps typically can supply 30 to 45 gallons of fuel per hour. All fuel injection pumps will have an amperage draw of approximately 5 amps per hour. Each injector draws approximately 1 amp so a four injector system would draw an additional four amps under full utilization. In this case your charging system will need to support 9 amps without discharging the battery. Automotive applications have virtually no trouble in this regard but motorcycles need to be looked at on a case by case basis.
3. Fuel Injectors. RSR uses Bosch pintle style injectors These give the best atomization and widest spray pattern of any injector. We only use saturation style or high impedance injectors that have coil (Ohm) resistance of 12 to 16 Ohms. Low impedance injectors (2 to 3 Ohms) will not work with your RSR ECU. Disc style injectors are some what less efficient but will work with the RSR system. The fuel injector employs an electric solenoid which is triggered by the ECU for en opening duration of 1.5 to 16 milliseconds (Ms). Due to physical operating limits injectors are not reliable below 1.5 Ms as fueling at this low threshold will become erratic and unpredictable. At the other end of the range the injector should never be held open longer than 16 Ms. If the injector stays continuously open we say the injector is going 'Static'. This static figure or Ms value varies with the engine rpm because as the rpm increases there is less and less time for the injector to open and close. For example at 14,000 rpm the injector goes 'Static at 4.28 Ms. This is 60 seconds x 1,000 Ms divided by 14,000. Unfortunately the injector cannot, due to physical limitations, open and close instantly so a corrected 'Static' figure is less than this figure. This means at 14,000 rpm you cannot hold the injector open longer than 4.28 Ms or the injector will stay open all the time and go 'Static'. Understanding the physical limits and flow rates of individual injectors is critical to a fuel injection systems success.
4. Fuel Pressure Regulator. RSR uses Bosch fuel injection regulators. We set all of our systems at a nominal 51 psi of fuel pressure above manifold pressure. Fuel not used by the engine must be returned to the gas tank preferably above the fluid level in the tank which keeps the 'fuel-head pressure' from influencing injector rail pressure. This by-pass fuel must be returned to the fuel tank and not looped back to or 'T'ed' into the fuel pump entry. 'Looping' the return fuel to the pump will cause the pump to overheat. The purpose of the fuel pressure regulator is to maintain a constant supply of fuel to the fuel injectors. The regulator has a diaphram which is connected by a vacuum line to the inlet manifold below the throttle body butterfly. By referencing fuel pressure to manifold pressure the system will maintain a constant 51 psi above manifold pressure whether it is at 28 inches of vacuum or 30 pounds of boost. At 30 psi of boost the line pressure would be 81 psi or exactly 51 psi above manifold pressure. Because we are using a digital control of the fuel system we must use a fuel pressure regulator to keep fuel delivery a constant for accurate fuel delivery.
5. Manifold Absolute Pressure Sensor (M.A.P. Sensor). The RSR system uses AC-DELCO M.A.P. sensors in one, two or three bar pressure ranges. One bar sensors are for normally aspirated applications (28 inches to zero inches of vacuum). For turbo or supercharged applications two bar (to 15 psi boost) or three bar (to 30 pounds boost) are available. On engines with low vacuum signals that do not approach 28 inches of vacuum the AUTOCAL Software interface allows rescaling to improve resolution during the development of your base fuel map. The RSR ECU constantly monitors the engine's manifold pressure using the super accurate pressure transducer. By mounting the M.A.P. sensor externally we are able to achieve a threefold advantage over other fuel injection systems which count the pressure transducer inside the ECU. First, we are able to easily switch one, two or three bar sensors depending on the application without having to use a different ECU. Secondly, any pressure transducer or M.A.P. sensor must be mounted close to the inlet manifold. Using a standard 5/32 inch vacuum line this distance should not exceed 18 inches. If you mount the ECU in the passenger compartment or in the tail section of a motorcycle this vacuum line would have to be much longer than 18 inches causing a loss of signal and resolution making the fuel injection less accurate and predictable. The RSR external AC-DELCO M.A.P. sensor can be mounted close to the inlet manifold and the ECU can be mounted separately in its optimum location. Thirdly, any M,A.P. sensor must be counted above the inlet manifold to prevent the condensation and accumulation of gas, oil, or water vapors at the M.A.P. sensor. The accumulation of these liquids will render useless any pressure transducer after a short period of time.
6. Throttle Position Switch (T.P.S.). The T.P.S. in the RSR system is used primarily to signal the ECU to initiate accelerator pump fueling. In addition the T.P.S. signals the ECU when throttle openings exceed 50%, the point where the programming kicks the ECU out of closed loop or oxygen sensing mode. The T.P.S. additionally will tell the ECU that under deceleration when the butterfly is closed the idle air control motor should open to by-pass air to prevent engine stalling. Unlike N-Alpha Systems which measure throttle angle as a major proponent of the preprogrammed fueling the RSR system does not use the T.P.S. for this function. If the T.P.S. fails you would only lose the accelerator pump and the above mentioned features but the machine would still operate.
7. Idle Air Control Motor (I.A.C.). All RSR systems feature an I.A.C. which allows you to use programming to set the idle speed during cold start warm up and normal operations. This feature eliminates the need for manual chokes or idle air by-pass screws. In addition under high speed deceleration with the throttle closed the I.A.C. will automatically by-pass air to prevent the engine from stalling. This computerized control over your idle circuit is the most sophisticated method of controlling these operating conditions. Should you chose not to use the I.A.C. or should the I.A.C. fail all RSR throttle bodies have provision to set the butterfly manually for idle air by-pass. Failure of the I.A.C. will not stop the operation of the RSR system. The I.A.C. is a standard AC-DELCO part available worldwide.
8. Engine (Oil or Water) and Air Sensors. The RSR system measures both coolant and inlet air temperatures. Using AUTOCAL software you are able to program the specific needs of your application in regard to warm up and other operating cycles. These sensors are easily obtained AC-DELCO parts which are extremely reliable in operation. Were you to damage a sensor, cut a sensor wire or otherwise render a sensor inoperative the RSR injection system would continue to operate. Without sensor input you would lose only the sophisticated programming which calibrates final injector timing on temperature variations.
9. Oxygen Sensor. The oxygen sensor is a measuring probe for determining the oxygen content of the exhaust gas. Since the amount of the oxygen in the exhaust indicates precisely how complete the combination of the air-fuel mixture in the cylinders is, the oxygen sensor feedback in closed-loop operation enables virtually complete combustion to take place. When in closed-loop the sensor tells the ECU to maintain mixture at 14.7 to I air-fuel ratio, giving fantastic mileage and very smooth running.
10. Throttle Bodies. All RSR systems are designed for maximum air flow. We assume your application is oriented towards high performance at a level above existing carburation. No matter how accurate or sophisticated the RSR digital fuel injection, if the throttle bodies are undersized optimum air flow will be limited and peak power will be compromised. RSR offers a wide range of throttle bodies to cover any possible application. All RSR systems are port injection i.e. the fuel injectors are located in separate inlet tracts, not in a common throttle body or plenum. Our throttle bodies are designed for true port injection and are not carburetor replacing throttle body injection units. Throttle bodies are 4Omm
11. IBM PC/Compatible AUTOCAL Software Interface. All our RSR systems use a nine pin serial cable to connect your PC directly to the RSR ECU. A user friendly software program called AUTOCAL is used to recalibrate or tune your RSR fuel injection system. AUTOCAL stands for automatic calibration. This means our AUTOCAL Software has the ability to automatically, through a set of adaptive programming algorithms write a base fuel map for your particular machine. A basic knowledge of IBM PC DOS is required to operate this software. There is no need to be afraid if you have zero knowledge of PC operations as the AUTOCAL program is extremely user friendly. Even if you have a phobia concerning computers you will find that taking just 30 minutes to learn how to turn on the computer, insert the AUTOCAL disc and follow some simple instructions is far easier than soaking your hands in gasoline and changing brass jets. Two versions of AUTOCAL are available. The user version comes with your RSR system. This allows you to make quantitative changes in each of the various programming functions. This allows you complete control over the base fuel map and certain other functions but does not allow you to change the shape of many of the program curves, response times or program boundaries. Our optional developmental software allows complete control both quantitatively as well as qualitatively. Using the AUTOCAL Developmental Software you can change the shape of warm up curves, air temperature correction curves and any one of 36 separate program menus and sub functions. This is an extremely powerful developmental tool that takes some time to become proficient with. Using the AUTOCAL Developmental Software you will have total control over your ECU programming and be able to calibrate the fuel delivery perfectly for your application.
RSR FUEL CALIBRATION FEATURES
The most difficult aspect of tuning whether it is fuel injection or carburation is getting the fuel delivery curves exactly right for your application. In the case of fuel injection this means getting your base map exactly correct for the various combinations of manifold pressure and engine rpm. RSR provides you with the tools necessary to completely map your engine. We realize that you do not have a $200,000.00 computerized dyno facility or a $10,000.00 exhaust gas analyzer. Our AUTOCAL software gives you both digital and analog read-outs of air/fuel ratios and engine load factors to speed your developmental process. You can manually edit point by point your base fuel map using these digital and analog read-outs or you can use the autocalibration mode and let the electronics write your base map during actual driving or dyno runs. By using the autocalibration mode and fine-tuning individual points in the manual edit mode you will be able to make a fuel map perfectly suited for your particular application. If you are unable to use a portable PC while the vehicle is moving we offer an inexpensive portable onboard readout of real-time air/fuel ratios and a booklet showing you how to use this display to develop your base fuel map. Using this portable display while driving and a computer to program your ECU you will be able to fully develop your base fuel map without the need for expensive and difficult to obtain dynamometer time. If you have access to a sophisticated dynamometer you can shorten your development time simply by using the on screen displays shown in the AUTOCAL program which tell you exactly how much fuel to add or subtract at any given point in the base map. Fuel calibration is a difficult process which cannot be completed on a dynamometer alone. Actual driving cycles are necessary to adjust your programming to provide accurate transition fueling. Whether you use our portable air/fuel ratio meter or take a ni-cad powered portable PC along for the ride you will have to drive the vehicle to perfect the fuel injection program. RSR calibrates specific systems but we cannot develop the programming for every possible application. Our software and support instrumentation will allow you to quickly perfect the RSR system on your particular vehicle.
ON-BOARD DIGITAL AIR/FUEL RATIO METER
This is the best investment I ever made Powered by The vehicle's 12 volt system this meter is directly connected to the Bosch Lambda oxygen sensor located in The exhaust system. The meter has a 10 L.E.D. display consisting of three green, four yellow, and three red lights. These lights represent a digitized instantaneous readout of air/fuel ratios ranging from 16~8:1 to 10.3:1. I can instantly 'see' My airifuel ratio and make adjustments based on this information. There is no need to look at The spark plugs or to guess if the motor is 'rich' or 'lean' at any one point to include transitional fueling. On closed loop RSR fuel injection systems the display will show oxygen sensing as well as all other functions such as accelerator pump fueling and high speed fuel cut-out on deceleration. Using this on-board meter I can quickly develop A base map.
FUEL INJECTION COMPONENTS
FUEL INJECTION FILTERS: Fuel injectors and injection fuel pumps should not be operated without filters designed specifically for fuel injection. Gas tanks and in-tank filters cannot be trusted to provide the filtration necessary to guarantee trouble-free long term operation of pumps and injectors. The fuel pump must be prefiltered to a 70 microns or less and the fuel injectors to an even finer degree (5 microns). Do not use any 'billet aluminum' style filters that use sintered bronze or paper elements as these are too restrictive and do not provide the filtration capacity necessary.
FUEL INJECTOR SIZING: To select a proper injector for your application you need to know the intended peak horsepower and of course the number of injectors in the system. We use the well agreed upon Brake Specific Fuel Consumption (BSFC) figure of .5 lb fuel/hp. hour for most engines. For example on a 3OOhp 8 injector RSR system: 3OOhp x .5 lb fuel/hp hr.: 150 lbs fuel/hr. 150 lbs fuel/8 injectors : 18.75 lb/hr injectors @ l00% duty cycle. A conservative correction factor would be to run the injectors at a 70% duty cycle as you should never hold the injectors wide open or 'static'. To calculate the injector size divide the calculated static figure of 18.75 lb/hr by .7. This gives you 26.76 lbs/hr or a 25 lb/hr injector. In this application your injectors would be using a 70% duty cycle to maintain a constant 300 hp. A simple formula is
Horsepower x .5 lb/hr. = lb/hr per
.7(# of injectors)----------injector
If you wish to correlate cc's per minute to lbs/hr. lO5cc per minute equals 10 lb/hr. Thus an injector that flows 315cc per minute flows 30 lb/hr.
The RSR Fuel Injection System is calibrated at 51 psi of fuel pressure at 0" vacuum. If you use A Adjustable Fuel Pressure Regulator you can calculate alternative injector delivery rates, stated in lbs/hr by using the following formula:
New Rate = New Fuel Presssure psi(51) X Injector rate @ 51psi