Speed density what is

Most systems can not read at higher horsepower levels. Speed Density Speed density systems calculate the density of the air first by measuring the temperature of the inlet air and manifold pressure. Advantages Less restriction in the intake tract More freedom in the intake tract Able to measure air consumption on very high horsepower builds where a MAF sensor might be limited.

Able to read boost if equipped with a greater than 1 Bar map sensor Free from errors encountered in MAF fouling. Works better with large cams where reversion affects reliability.

Disadvantages Is a little more difficult to tune Relies on a well tuned Volumetric Efficiency Table Less forgiving to new modifications to the engine Might have errors in large weather changes however a proper tune makes this minimal if any error.

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Sign-In to Your Account. Engine rpm is provided via a tach signal, while vacuum is transmitted via an intake manifold-mounted Manifold Air Pressure MAP sensor. Since air density changes with air temperature, an intake manifold-mounted sensor is also used. Production-based Speed Density computers also utilize an oxygen O2 sensor mounted in the exhaust tract.

This helps compensate for wear and tear and production variables. Other sensors on a typical Speed Density system usually include an idle-air control motor to help regulate idle speed, a throttle-position sensor that transmits the percentage of throttle opening, a coolant-temperature sensor, and a knock sensor as a final fail-safe that hears detonation so the computer can retard timing as needed.

All ''87 and '88 non-California Ford 5. Most Mopar fuel- injection systems have used Speed Density too. Because a Speed Density system still has no sensors that directly measure engine airflow, all the fuel mapping points must be preprogrammed, so any significant change to the engine that alters its VE requires reprogramming the computer. Mass Flow By contrast, Mass Air Flow MAF systems use a sensor mounted in front of the throttle body that directly measures the amount of air inducted into the engine.

The most common type of mass-flow sensor is the hot wire design: Air flows past a heated wire that's part of a circuit that measures electrical current. Current flowing through the wire heats it to a temperature that is always held above the inlet air temperature by a fixed amount. Air flowing across the wire draws away some of the heat, so an increase in current flow is required to maintain its fixed temperature.

The amount of current needed to heat the wire is proportional to the mass of air flowing across the wire. The mass-air meter also includes a temperature sensor that provides a correction for intake air temperature so the output signal is not affected by it. Intake air temperature sensors? It all seems a little confusing, but no fear, iWire is here! Before we get started a quick glossary of acronyms will help:. SD - Speed Density. What is Speed Density?

Speed Density is a tuning method where the ECU uses information based on manifold pressure and temperature using the MAP sensor and an added IAT sensor to calculate how much air is coming into the engine.

These tables allow predicted airflow values to be more closely adjusted to observed reality. Moates Support. Search for:. Theory: Speed-Density Categories: All Articles , How Tuning Works Introduction If you do not have a strong background in physics and chemistry, be prepared to do a lot of reading in the numerous side links on this page. Sometimes called different things by different manufacturers. I will use IAT here. Displacement : the volume swept by a piston descending from the top to the bottom of the cylinder bore.

More here. Usually stated as a ratio, i. Stoichiometric AFR varies from fuel to fuel. Lambda : similar to AFR, except usually expressed as a number where 1. Lambda and AFR are the same concept expressed in different units.