1. What volumetric efficiency (VE) is
This guide is for tuners and calibrators who will set up and tune VE mode. The driver who does not tune the engine will find the essentials in this chapter, through the end of the section Where to choose the strategy, which includes the nitrous warning.
In this guide, the VCU (FT700 or FT470) is the electronic control unit (some screens call it the ECU) that runs the map and commands the engine's fuel injection. FuelTech Vision is the computer program in which you edit the map and write it to the VCU. The technical terms are in the Glossary, at the end of the guide.
Volumetric efficiency (VE) is the ratio between the air that actually enters the cylinder on each cycle and the air that would fit in its displacement at the manifold conditions.
The intake manifold is the duct that carries the air to the valves. The manifold conditions are the absolute pressure and the temperature of the air there, just before the intake valve.
With a VE of 100%, the cylinder receives the same mass of air that its displacement holds at that pressure and temperature. With a VE of 80%, it receives 80% of that mass.
Because pressure and temperature enter the calculation separately, VE describes only how well the engine fills. It does not say how hard the engine is working: it is not a load index.
#Why VE changes with engine speed and load
Filling depends on how the engine breathes in each condition: camshaft, intake and exhaust ports and runners, and how long the valve stays open at each engine speed.
For this reason VE has a value for each engine speed and for each manifold pressure, and the VE table has these two axes.
VE is referenced to the manifold pressure. In a turbo engine, if the absolute pressure doubles, the air mass doubles from the pressure itself, and the VE does not need to double.
In the FuelTech Vision default map, the VE is the same from +1.0 to +3.4 bar at each engine speed: between 82% and 104% from 3000 to 7000 rpm.
The screen accepts a VE from 0 to 300%, and going over 100% is possible. A VE above about 115% is a warning, not a ceiling for the table: check the injector flow rate, the fuel pressure and the air temperature sensor, as Step-by-step tuning method explains.
#Pulsewidth mode and VE mode
The VCU has two injection strategies.
In pulsewidth mode (Injector Pulsewidth), the main table stores injection time in milliseconds. Those milliseconds are valid for the injector, the fuel pressure and the fuel with which the map was tuned.
In VE mode (VE Based), the main table stores only the engine's VE, in %. The VCU calculates the milliseconds in real time, from the air mass, the fuel, the lambda target and the injector data. Lambda measures the mixture: 1 is the chemically correct mixture, below 1 is rich, above 1 is lean.
| Item | Injector Pulsewidth | VE Based |
|---|---|---|
| Main table | injection time in ms, per bank | Main MAP VE table, filling in % |
| Load axis | manifold pressure or throttle, according to the Main fuel table field | always the manifold pressure (MAP) |
| Air temperature | compensation table in % | enters the calculation in kelvin |
| Injector, pressure and fuel | built into the milliseconds of the table | entered separately and used in the calculation |
| Deadtime (injector opening delay) | reference value, built into the map | full value from the table, added to each pulse |
#What you gain with VE mode
- Change the injector, pressure or fuel without redoing the table. You enter the new data and the VCU redoes the calculation, as long as the data is right (see the box below); after a fuel change, check the mixture with the O2 sensor.
- Separate lambda target. Changing the target changes the fuel right away, without touching the VE.
- Pressure and air temperature through the gas law. There is no air temperature compensation table to tune.
- Closed loop and learning. The VCU compares the wideband O2 sensor (the sensor in the exhaust that measures the burned mixture) with the target and corrects the VE used. The learning stores that correction by region, and you decide when to move it to the table. In this guide, "O2 sensor" always means this wideband sensor.
The closed loop and the learning (LTFT, long-term fuel trim) are in VE closed loop and in Self-learning: VE learning (LTFT).
#Where to choose the strategy
The choice is in Engine Settings > Engine settings, Fuel strategy field: Injector Pulsewidth or VE Based.
Changing the strategy does not convert the map. Each mode has its own tables; the functions of the other mode stay off, stored in the map, and come back if you go back.
To take a pulsewidth map to VE, see From the pulsewidth map to VE.
If you use nitrous, first read the section What does not run in VE mode, in Enrichments and compensations in VE mode: in VE mode the Pro-Nitrous fuel (the VCU nitrous function that adds fuel per bank and per cylinder) and the PWM progressive nitrous fuel are not applied, and the mixture goes lean when the nitrous is activated. With nitrous, use Injector Pulsewidth or do not activate the nitrous in VE mode.
Engines with individual throttle bodies and high-overlap camshafts have their own precautions: see What makes VE advanced, and the limits.
#What this guide covers
This guide describes FuelTech Vision 3.0 with VCU firmware 00.03.00.54, on the FT700 and FT470 VCUs.
In another software or firmware version, screens, defaults and behaviors may change.
The FT470 runs the same firmware and the same VE mode as the FT700: the same VE table, the same lambda target, the same closed loop with learning and the same acceleration fuel enrichment.
What changes is the number of inputs and outputs, the number of internal wideband O2 sensor conditioners and the log speed. The details are in Before you start: engine, fuel, injectors and sensors.
The results expected in this guide come from the calculation the VCU makes, not from engine measurements: the tests in True VE show how to check on your car.
Names of screens, menus, parameters and log channels appear in bold, as FuelTech Vision shows them in English.
The MAP appears as on the screen, in gauge pressure. When the calculation uses absolute pressure, the text says so. Pressures are in bar (1 bar = 14.5 psi) and temperatures in °C.
#Reading path
- If you are coming from the pulsewidth map: read How the VCU calculates fuel in VE mode, Before you start: engine, fuel, injectors and sensors, Enrichments and compensations in VE mode, From the pulsewidth map to VE, VE closed loop and Self-learning: VE learning (LTFT), in that order.
- If you want proof that it is true VE: read How the VCU calculates fuel in VE mode, True VE and What makes VE advanced, and the limits.
- If you are going to tune a car: read Before you start: engine, fuel, injectors and sensors, The tables: VE, lambda target, axes and grids, Enrichments and compensations in VE mode, VE closed loop, Self-learning: VE learning (LTFT), Reading the log: the VE channels and Step-by-step tuning method. A new or converted map goes first through From the pulsewidth map to VE.
- Before starting the engine in VE mode: check the Before the first start list, in From the pulsewidth map to VE: it gathers the factory defaults that change the fuel.
- For reference: Diagnosis: symptoms and causes, Parameter reference and Glossary.