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SAFR Fuel Tuning


POWER SPORTS AND ELECTRONIC FUEL INJECTION GLOSSARY

FAT BOY

Harley-Davidson released a motorcycle in 1990 based on the FLST Heritage Softail. They called it the FLSTF or Fat Boy and it is immediately recognized by its solid cast disc front wheel.

FATHEAD

The Twin-Cam engine (V-Twin, produced from 1999 - Current Day)

FLATHEAD

The Flathead engine (V-Twin, produced from 1929 - 1972)

FLOW RATE METER

Device used in many injection systems.

FOUR-STROKE ENGINE

This is the most common engine design found in street motorcycles today. It refers to the number of times a piston moves up and down through each power cycle. 1) A downward stroke brings in the fuel/air mixture; 2) an upward stroke compresses the fuel/air mixture; 3) a downward stroke results when that mixture is ignited and expands, and finally; 4) an upward stroke expels the exhaust gases.

FRESH GAS

The fresh mixture drawn into the cylinder is a combination of fresh air and the fuel entrained with it. While most of the fresh air enters through the throttle valve, supplementary fresh gas can also be drawn in through the evaporative-emissions control system.

FUEL ACCUMULATOR

The fuel accumulator maintains the pressure in the fuel system for a certain time after the engine has been switched off in order to facilitate restarting, particularly when the engine is hot. The special design of the accumulator housing is such that it deadens the sound of the electric fuel pump.

FUEL CONSUMPTION

The effects of timing advance on fuel consumption are the exact opposite of its influence on emissions. If the combustion sequence is to remain optimal at higher excess-air factors (lambda), then ignition timing must be advanced to compensate for the slower combustion rate. Thus advanced ignition timing means lower fuel consumption and more torque.

FUEL DELIVERY

The electric fuel pump continuously pumps fuel from the tank and through the fuel filter to the central injection unit. Fuel pumps are available as in-line or in-tank versions.

FUEL DISTRIBUTOR

Depending upon the position of the plate in the air-flow sensor, the fuel distributor meters the basic injection quantity to the individual engine cylinders. The position of the sensor plate is a measure of the amount of air drawn in by the engine. The position of the plate is transmitted to the control plunger by a lever.

FUEL FILTER

The fuel filter retains particles of dirt which are present in the fuel and which would otherwise have an adverse effect on the functioning of the injection system. The fuel filter contains a paper element with a mean pore size of 10mm backed up by a fluff trap. This combination ensures a high degree of cleaning.

FUEL FILTRATION

Fuel-borne contaminants and impurities can prevent the injectors and fuel-pressure regulator from operating correctly. A filter is therefore fitted in the fuel line between the electric fuel pump and the central injection unit, preferably in a position underneath the vehicle protected against stone-throw.

FUEL LINES

Fuel lines must be installed so that they cannot be adversely effected by torsional motion, engine movement, or similar, phenomena.

FUEL METERING

The task of the fuel-management system is to meter a quantity of fuel corresponding to the intake air quantity. Basically, fuel metering is carried out by the mixture control unit. This comprises the air-flow sensor and the fuel distributor.

FUEL-PRESSURE ATTENUATOR

The injectors operating cycles and the periodic discharge of fuel that characterizes the positive-displacement fuel pressure. Under unfavorable circumstances, the mountings for the electric fuel pump, fuel lines and fuel rail can transmit these vibrations to the vehicle's body.

FUEL-PRESSURE REGULATOR

The injected fuel quantity should be determined exclusively by injection duration. Thus the difference between the fuel-pressure in the fuel rail and the pressure in the intake tract must remain constant. A means is thus required for adjusting the fuel pressure to reflect the variations in the load-sensitive manifold pressure. The fuel-pressure regulator therefore regulates the amount of fuel returning to the tank so that a constant pressure drop is maintained across the injectors. With multi-point injection, the pressure regulator is generally positioned at the far end of the fuel rail to avoid impairing the flow within the rail. However, it can also be mounted in the fuel return line.

FUEL PUMP DEGASSER

Device fitted to the fuel system downstream from the pump.

FUEL RAIL

Contaminants in the fuel can impair the operation of both pressure regulator and injectors. A filter is therefore installed downstream from the electric fuel pump. This fuel filter contains a paper element featuring a mean pore diameter of 10hm. A black plate retains it in its housing. The replacement intervals are determined by the filter's volume and contamination levels in the fuel.

FUEL SYSTEM

The fuel-supply system must be capable of providing the engine with the required quantity of fuel under all operating conditions. An electric pump draws the fuel through a filter while extracting it from the tank for delivery to the fuel-distribution rail with its electromagnetic injectors. The injectors spray the fuel into the engine's intake tract in precisely metered quantities. The excess fuel flows through the pressure regulator and back to the fuel tank.

FUEL TANK

According to the German equivalent of the FMVSS/CUR, the fuel tank must be corrosion-resistant and not leak even at a pressure defined as double the normal operating pressure, but al least at 0.3 bar overpressure. Suitable openings, safety vavles etc. must be provided to permit excess pressure to escape. Fuel must not escape past the filler cap, nor through the pressuree-qualization devices. This also applies in the case of roas shocks, or in curves, or when the vehicle is tilted. The fuel tank must be remote from the engine so that the ignition of the fuel is not to be expected even in the event of an accident. Further, more stringent regulations apply in the case of vehicles with open cabs, and for tractors and buses.

FULL-LOAD ENRICHMENT

The engine delivers its maximum torque at full load, when the air-fuel mixture must be enriched compared to that at part-load. In contrast to part-load where the calibration is for minimum fuel consumption and low emissions, at full load it is necessary to enrich the air-fuel mixture.


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