VE tuning: what the VE table does and how to tune it

What the VE table does

Volumetric efficiency (VE) is how well the engine fills its cylinders with air, compared with its displacement. On a speed-density setup the ECU estimates the air in each cylinder from manifold pressure (MAP), RPM and air temperature, uses the VE table to correct that estimate, and injects fuel to match the target mixture.

The table is indexed by RPM and load, usually MAP. Its numbers carry everything the simple air calculation misses, so they aren't always a literal measure of breathing. What matters is that each cell gives the right amount of fuel, which you confirm with a wideband oxygen sensor.

On alpha-N setups, load is throttle position instead of MAP. That suits individual throttle bodies and big cams, where MAP is unsteady at low RPM.

How common ECUs use VE

Speeduino

A 16×16 VE table in %, with the load axis set by the fuel load source: MAP for speed density, TPS for alpha-N. Pulse width starts from Required Fuel. Options to multiply VE by the MAP ratio and to include the AFR ratio change what the VE numbers mean, so changing either means retuning VE.

rusEFI and epicEFI

A 16×16 VE table, with a fuel algorithm of Speed Density, Alpha-N, MAF and others. There is no Required Fuel setting. Fuel is worked out from displacement and injector flow, and the target mixture comes from a lambda or AFR table.

MegaSquirt MS3

16×16 VE tables, with an algorithm of Speed Density, Percent Baro, Alpha-N, MAF or ITB, and Required Fuel from the ReqFuel calculator. AFR targets are a separate 12×12 table.

TunerStudio

TunerStudio shows these tables as the INI declares them. Its registered version includes VE Analyze Live, which corrects VE from wideband data using the INI's [VeAnalyze] section.

A safe order for tuning VE

1. Calibrate the sensors first: MAP, coolant and air temperature, throttle position and the wideband. Check ignition timing with a timing light.
2. Set the injector data and Required Fuel (or injector flow and displacement) before touching VE. The injector sizing guide covers this.
3. Set the AFR or lambda targets. VE is tuned to reach the targets, so changing targets later moves the fuelling.
4. Tune with a warm engine. Warm-up enrichment is a separate curve.
5. Start at idle, then light cruise, then more load. Steady conditions first; acceleration enrichment is tuned separately.
6. Leave full load and boost until last, and tune them in small steps with knock detection.
7. Smooth as you go. Neighbouring cells should agree, VE should rise or flatten with MAP, and full-load VE should peak near the engine's torque peak.

Correcting a cell from wideband data

If a cell runs rich or lean of target, scale its VE by measured over target: new VE = old VE × measured AFR ÷ target AFR, or the same with lambda. A cell aiming for 14.7 that reads 13.2 is rich, so its VE drops to about 90 % of what it was.

• The wideband reads a few hundred milliseconds behind the engine. Line the reading up with the cell the engine was in when that exhaust left the cylinder.
• Ignore readings during deceleration fuel cut, gear changes and throttle transients.
• If closed-loop correction is active, include it. A cell that only reads on target because closed loop is adding 8 % still needs 8 % more VE.
• Use several samples per cell. One reading moves the cell on noise.

Using efi2000 for VE tuning

A starting table

Generate tables builds a starting VE table, with AFR target and spark tables, from the engine details in Vehicle properties. You preview it before applying it, so your first start begins from a sensible tune instead of a blank one.

Log coverage

Overlay a log on the VE table and see, cell by cell, how much data you have and how far off the mixture was. Cells your logs never reached are marked, so you know what's tuned and what's still a guess.

Autotune

Autotune compares measured AFR with your target and proposes VE corrections while you drive, at idle or from a log you already recorded. It uses the same VE Analyze settings your firmware's INI already defines. A separate warm-up mode tunes warm-up enrichment.

• It only learns from readings it can trust, and filters out the rest.
• Changes are kept small and smooth, so one bad pass can't wreck a table.
• It won't propose a change that Spotter would flag as unsafe, and won't add fuel the injectors can't deliver.
• Full load and boost are opt-in. While you drive, it tells you to lift off on lean mixture or knock, and to ease off when the engine runs hot.

Checks

Spotter reviews the VE table's shape and flags the cells that look wrong, so you catch mistakes before they reach the engine. Target tracking shows how closely AFR followed target at idle, cruise, full load and boost.

Questions

What is a good VE value?

There isn't a universal number. What a VE value means depends on the firmware and its settings, such as Required Fuel and whether MAP is multiplied in. The shape matters more: VE should rise with MAP and peak near the torque peak.

Can I tune VE without a wideband?

Not reliably. A narrowband sensor only tells you rich or lean of stoichiometric, so it can't confirm a full-load or boost target. efi2000's autotune needs a working wideband.

Should closed-loop correction be on while tuning VE?

It can be, as long as you account for it. A correction of +5 % means the VE cell is 5 % short. efi2000's autotune takes the correction into account for you.

Does efi2000 autotune work with a TunerStudio tune?

Yes. Import the MSQ and INI into a project, autotune it, and the tune saves back to MSQ.