Fuel injection offers a powerful, low maintenance alternative for 600cc micro sprint racing. It is important to choose the fuel injection system that is appropriate for your needs. After carefully choosing your fuel injection system, proper tuning is imperative. Maintaining the optimized performance that you attained from dyno tuning requires a basic maintenance program. With a few simple weekly steps, you can keep your system in top notch condition.
Fuel Injection vs. Carburetors
In the past, carburetors ruled the track, but made tuning difficult with often substandard results. Fuel injection is the perfect solution to the “carburetor headache” that we’ve become so accustomed to. With the appropriate knowledge and a good technical support team, even the novice racer can find great success with fuel injection.
There are several fundamental differences between carburetors and fuel injection. Though both may be capable of similar peak horsepower numbers, actual “on-track” performance characteristics vary greatly. On track performance begins with a strong tuning program. When tuning carburetors, there are very limited tuning opportunities for wide-open-throttle adjustments, mostly limited to main jet changes. Conversely, fuel injection allows a tuner to make adjustments at every 250 RPM’s in addition to 10 throttle positions. Successful fuel injection tuning requires little or no compromise. Carburetors force you to compromise between reach and lean areas in the fuel curve to find that “happy medium”. In order to make some areas run at optimum performance, it causes the tuner to compromise the fuel curve with other areas being too rich and/or too lean. A fuel injection system allows the tuner to make far fewer compromises due to the highly increased adjustment capabilities.
Fuel Injection vs. Carburetors on the Dyno  |
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Carburetors must be re-jetted for altitude and atmospheric changes. This includes adjusting air/fuel for simple changes in the weather. Properly tuned fuel injection systems have sensors that direct the computer to automatically adjust for these changes with no need to retune at all. Fuel injection systems have the ability to “self-preserve”, meaning that if something happens to cause the engine to overheat, the system will detect this condition, it will automatically make changes, like add additional fuel and retard the timing to preserve the engine for as long as possible. Carbureted systems have no ability to “self-preserve”.
Fuel Injection System Selection
Making the most out of a fuel injection system begins with the system selection. Not all fuel injection systems are the same and there are many things to take into consideration before making a purchase. The most important part of any fuel injection system is the actual injector and its placement. It’s extremely important that the injector’s placement allows it to aim fuel directly at the intake valve. The fuel vaporizes when it makes contact with the hot valve, delivering the entire, finely atomized, fuel load into the cylinder. If the injector is not aligned properly or has an incorrect spray pattern, it will deliver fuel directly against the intake wall causing a poorly atomized fuel mixture, as well as inconsistent and poor combustion.
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Correct Injector Angle | Incorrect Injector Angle |
Another important aspect of the injector is its response time, or the time it takes to open once energized. At 15,000 RPM, the injector has only 4 milliseconds to deliver its entire fuel load while the intake valve is open. The stock fuel injector only takes 1 millisecond to open, while some of the older, larger design injectors with their heavy internal parts take up to 1.8 milliseconds to open. That takes up nearly half the time available to deliver the fuel load and much too long for optimum high RPM performance. Due to cost and availability, these larger, old-style injectors are widely used in most fuel injection conversion systems. It’s also important that the fuel flow rates are closely matched across all injectors in the system. This maintains even fueling across each cylinder allowing air/fuel ratios to remain constant while maximizing efficiency. It is also extremely important that the injector selected is appropriate for your fuel requirement. For example, if you use alcohol to fuel your racecar it is important that the fuel injectors selected are appropriate for use with alcohol. Finally, electrical compatibility is a must in order for your system to function properly. The stock fuel injection controllers are designed for “saturated” injectors. These injectors have a high coil resistance (12 to 18 ohms) and only draw about 1 amp. The other type injector is a peak/hold injector. These injectors have a low coil resistance (1 to 5 ohms) and require a special injector driver circuit for proper control. If a peak/hold injector is used in a system designed for a saturated injector, the injector driver circuit can be permanently damaged.
In conjunction with the proper injector selection is fuel rail selection. Each fuel rail must be custom designed to handle the increased fuel requirements and hold the injector in place securely. A large plenum fuel rail is also important for even fuel flow to each injector. The stock fuel rail will not be able to supply the additional fuel required in an alcohol system. The fuel rail must allow for proper injector alignment and hold the injector securely.
Single vs. Dual Fuel Injection
Depending upon your particular set of rules, you may be able to choose between single or dual fuel injection systems. Single injection systems offer one injector near the intake valve. Most stock systems are single injection. Dual Injection offers one injector near the intake valve and one injector above the intake stack very far from the intake valve. Dual injection systems may be offered as an upgrade to older model engines or they may come stock on the newer generation of engines.
In a dual injection system, when the injector above intake stack is activated, the fuel travels much further and has more time to vaporize and take more heat out of the air. This generates increased mid-range performance. The lower injector is used for low rpm cruise and supplies additional fuel during quick throttle movements for best throttle response.
Adding dual injection to a single injection system always increases power in the mid-range. This increase in mid-range power can be valuable in two ways. First, the system can be left as-is to allow maximum benefit exiting the turn. Secondly, the engine can also be mechanically tuned for more top-end performance which would normally decrease the mid-range power, but since the dual injection adds mid-range power, there is no loss in mid-range power.
Fuel Injection System Optimization
After a fuel injection system has been selected, there are still several steps to optimization. Though system selection is very important, dyno tuning and proper maintenance is the key for success. A good system can run poorly when it has been set up improperly or if maintenance is neglected. Dyno tuning is the most efficient method for optimizing power. Since there is no such thing as a “generic” fuel curve or fuel map, dyno tuning each system individually is very important. You will want to be sure that the tuner you select is knowledgeable in your specific application and understands the importance of broad power curves and the theory behind internal combustion engines. Though it is easy to tune a system for high peak numbers, it is much less simple to tune for drivability and overall performance. You will also want to be sure that the dynamometer is best suited for your application. Choosing the right dyno will eliminate inconsistencies of the testing/tuning process. Be sure that you are tuning for all variables in the entire system so that maximum power can be achieved; these include fuel curve, intake stack length, exhaust system, ignition/cam timing, and air box. When you leave the dyno, you will not only have optimized your fuel curve for peak performance and maximum drivability, but you will also know prior to race day that your system is operating correctly.
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During the tuning process, your tuner should be asking questions about the type of track you race on and the driver’s experience. These are all factors that contribute to optimal tuning. Generally tuning for the “big” peak-power numbers does not make the best race engine. Big peak-power numbers are usually attained by sacrificing mid-range power which hurts the all-important corner exit performance. Different tracks and driving styles require different power curves. A track with long straights and tight turns requires very wide power curves that drive the car out of the turn and continue to pull to the end of the straight. Small tracks with sweeping turns and short straights might require a more narrow power curve for best performance.
Fuel Injection System Maintenance
In order to keep your system in top condition, proper maintenance is required. Luckily, maintenance on a fuel injection system is considerably easier than what is required for a carbureted system. Most importantly, don’t change anything. Your fuel map was optimized for your particular combination and changing any part of that could significantly decrease performance. In particular, your system was tuned in accordance with your exhaust, injection setup, airbox, fuel pressure, cam timing, and compression. Any of these, if altered, would likely harm performance. Weekly maintenance is also very important. You should flush your system with straight gasoline (absolutely no 2-stroke oil should be used) directly after each weekend of racing. This entails five simple steps:
- Disconnect the return line and put it in an empty jug.
- Disconnect the feed line from the tank and connect to a gas can
- Run the pump until gas exits the return
- Start/run the engine for about 5 seconds
- Disconnect gas can and cap the lines
Inspecting the system weekly (as well as careful initial installation) is also important for maintaining reliability. Be sure that all electrical components are mounted with the plug facing down to prevent water from gathering in the connector. Inspect all wiring weekly for loose, bad, or corroded connections. Pay special attention to the switches. You will also want to clean and inspect the primary fuel filter weekly.
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Overall, fuel injection can be a much less complicated solution than carburetors. It increases tuning opportunities while decreasing maintenance. When an injection system is properly tuned, there is no need to make changes for altitude or atmospheric conditions. For additional information on fuel injection, please feel free to contact Guhl Motors at 717-625-1411 or visit us online at www.guhlmotors.com. In addition to our winning line of fuel injection systems, we also offer “best-in-the-business” dyno tuning services, wire harness conversions, vehicle wiring systems, and full service fuel injection repair, as well as a variety of quality accessories.
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