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Do I need a tune for my LS swap?
Almost always, if it's fuel-injected. Here's what needs a tune and why.
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Tune checklist for your build: pick engine, computer, trans →
| Your swap or mod | Tune? | Why |
|---|---|---|
| EFI swap with the factory computer | Yes, always | Every donor PCM needs reprogramming: delete VATS (or the engine will not start), match injector size and MAF scaling, and match transmission settings; emissions monitors and speed limiters from the donor are also present. |
| Aftermarket cam | Yes | Idle, fuel, spark and torque-model changes; on AFM engines, the deactivation must be turned off too. |
| Bigger injectors | Yes | The injector size in the tune has to match the injectors installed. |
| Headers | Recommended | On EFI engines, tuning adjustments help get the full benefit from headers. |
| Heads, intake, stroker or power adder | Yes | A custom tune is crucial after these mods, and once you go past factory airflow or displacement, or add a power adder, upgrading the ECM or going standalone becomes essential. |
| Turbo or supercharger | Yes, carefully | Air/fuel ratio, timing and boost have to be balanced across the rpm range; use an experienced calibrator or dyno tuner. |
| Electronic transmission swap | Yes | The computer controls shift timing and line pressure, so its transmission settings must match. |
| Standalone EFI (e.g. Terminator X) | Yes | Self-learning helps, but even self-learning systems should be tuned properly. |
| Carbureted LS | No engine tune | Carb tuning plus an LS ignition controller with preloaded timing curves (a laptop fine-tunes it). |
PCM must be recalibrated to stop commanding deactivation; aftermarket cams also need idle, fuel, spark and torque-model changes.
The details
Specifics depend on your computer and operating system.
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- GM LS, LSA: Aeroflow's fly-by-wire throttle body needs a tune because it uses a different heavy-duty motor with different parameters than the standard unit.
- GM LS, LSA: The replacement throttle plate is 102 mm compared to a standard GM LS 87 mm unit, so intake manifolds may need clearancing for full throttle opening.
- GM LS, LSA: On the GM E38 computer, installing the 102 mm drive-by-wire throttle body requires adjusting the ETC area scaler plus throttle-position and airflow-correlation diagnostics.
- GM LS, LSA: Dyno tune the engine with the Aeroflow throttle body installed so it causes no engine damage.
- GM; most GM vehicles up to 2018 model year: Changing tire size or differential gear ratio can make the speedometer, odometer, and transmission shift points inaccurate, so the vehicle needs gear/tire recalibration.
- GM; most GM vehicles up to 2018 model year: On GM vehicles, gear and tire changes are corrected with the Gear/Tire Wizard in VCM Editor, which recalibrates the speedometer and scales the transmission tables.
- GM; most GM vehicles up to 2018 model year: The Gear/Tire Wizard's Auto Scale option automatically adjusts transmission tables to preserve similar shift RPM after a gear or tire change.
- GM; most GM vehicles up to 2018 model year: Skipping recalibration after a gear or tire change can cause poor shift quality, incorrect mileage tracking, and trouble codes.
- GM; most GM vehicles up to 2018 model year: The Gear/Tire Wizard function is supported on most GM vehicles up to the 2018 model year.
- In a VE-based fuel model, incorrect injector characterization data degrades the accuracy of the entire tune, especially the VE table and the ECU's ability to hit lambda targets.
- Injector setup is one of the first steps in the tuning process; without good injector data the whole fuel model is flawed.
- The fuel-pressure reference type (atmospheric vs manifold-referenced) must be set correctly because injector flow and dead time vary with differential fuel pressure.
- The fuel's stoichiometric AFR and specific gravity are key inputs to a VE-based fuel model and must be entered correctly.
- Gen IV LS, Gen V LT: After a DOD/AFM/DFM delete, the PCM or ECM must be recalibrated so it no longer commands cylinder deactivation.
- Gen IV LS, Gen V LT: With a stock-spec non-DOD cam, the main calibration change for a delete is generally disabling the deactivation function and its related diagnostic logic.
- Gen IV LS, Gen V LT: An aftermarket cam in a delete build requires adjusting idle airflow, fueling, spark, torque modeling, and other drivability tables, beyond simply switching deactivation off.
- Gen IV LS, Gen V LT: A software-only disable is not a mechanical delete: it leaves the original deactivation lifters and oil-control hardware inside the engine.
- Gen IV LS, Gen V LT: Installing conventional lifters while keeping the original deactivation cam can create uneven compression, misfire codes, and poor engine operation.
- GM P01 0411; Gen III LS: Combined changes in displacement, injectors, ethanol fuel, boost, and MAF removal required comprehensive changes to the 0411 (P01) computer rather than a minor tweak.
- GM P01 0411; Gen III LS: On early controllers, scaling the MAF signal for boost loses important resolution, which is a reason to convert to speed density instead.
- GM P01 0411; Gen III LS: A 3-bar speed-density custom operating system allows running up to 30 pounds of boost in this application.
- GM P01 0411; Gen III LS: The MAP sensor must match the selected custom operating system; a mismatched sensor severely corrupts global fueling.
- GM P01 0411; Gen III LS: The VE table tells the computer how much air enters the engine by RPM and MAP, so a speed-density conversion requires recalibrating that table from scratch.
- GM P01 0411; Gen III LS: A large cam typically lowers volumetric efficiency at low RPM and raises it at higher RPM, so the stock idle-region VE values become wrong after a cam swap.
- GM P01 0411; Gen III LS: Swapping to 1,000cc injectors required entering the supplied flow rate, offset, and short pulse adder data into the tune.
- GM P01 0411; Gen III LS: Converting to speed density required forcing the MAF to fail (0 Hz fail frequency) and reconfiguring the P0101, P0102, and P0103 diagnostics so no check-engine light is set.
- GM P01 0411; Gen III LS: Turbocharged engines can make boost at partial throttle and low RPM before ordinary RPM-based power enrichment activates, which is dangerous if boost enrichment is not calibrated.
- GM P01 0411; Gen III LS: Timing should be pulled in any table region that may see boost for safety, then walked back in on the dyno.
- GM P01 0411; Gen III LS: A displacement change requires correcting the cylinder volume in the tune: a 370 cubic inch V8 is 370 ÷ 8 = 46.25 cubic inches per cylinder.
- GM P01 0411; Gen III LS: A custom OS's initial maximum VE values guard against lean damage but prevent the engine from starting until baseline VE values are transferred in.