Turn-on tune: get your LS running
Everything you need to get a swapped LS started, idling and driving gently, step by step, with the values that real tunes run. Then take it to the dyno.
Read this first
This is what has worked for us, not a guarantee for your engine. Every build is different: cam, heads, injectors, fuel, altitude, converter and gearing all change what your engine wants. Use the numbers here as a starting point and let your logs decide.
A turn-on tune gets the engine started, idling and driving gently. It is not a finished tune. We always recommend a dyno tune, or a professional tuner with a wideband, before any wide-open pass. Do not flash it and go WOT. Keep it out of boost and off the top of the throttle until it has been tuned, and stop the moment you see knock, lean air/fuel or a pressure drop (our Don't blow it up checks).
Use at your own risk.
Build your turn-on tune sheet
Tell us about your build. You get every value a turn-on tune needs, where the number came from, and the walkthrough step that shows how to set it.
Based on 30 real tunes so far, 2 of them on a cam we can name. This grows as we add tunes.
We may earn a commission when you buy through links on this page.
Step by step: the values a turn-on tune needs
This is the order we set them in. Each step links to the full how-to in our HP Tuners walkthrough.
- Save the stock file and turn off VATS. Read and save the stock file before you change anything, and keep a copy. Turn VATS (anti-theft) off or the engine won't start. Keep a battery charger on for every write. How →
- Enter the known values. These are facts, not tuning:
- your injectors' real data from the maker;
- displacement;
- stoich for the fuel in the tank (gasoline about 14.7, E10 about 14.1, E85 about 9.8);
- gear ratio and tire size;
- fans;
- a sensible rev limit (6,000–6,200 rpm on a stock-valvetrain truck engine);
- for boost, MAP sensor scaling (GM 3-bar 12223861: linear 329.41, offset -6.35).
- Set the idle. Hot idle target, base idle airflow, idle spark, and cracker/follower so it doesn't stall coming back to idle. A cam is where most turn-on tunes need work. How →
- Leave fuel close to stock until you can log. Start with stock power enrichment (lambda about 0.85). Get the MAF or VE close from logs at part throttle before you push it. How →
- Keep spark conservative. Start at the low end of the ranges below, and never add timing without watching knock retard. How →
- First start and gentle drive. Check oil pressure, fuel pressure (about 58 psi on a factory-style LS system), trims within ±10%, and no knock retard. Then drive it gently and log. How →
- Then book the dyno. WOT fuel and spark get dialed in on a dyno, or with a pro tuner and a wideband, not on the street. Our pre-WOT checks →
What real tunes run
Ranges from the real LS tunes we've pulled apart, by computer family and NA vs boost. They are what experienced tuners settled on for those builds, not targets for yours.
| Setting | Gen III, NA | Gen III, boosted | Gen IV, NA | Gen IV, boosted |
|---|---|---|---|---|
| Hot idle target | 800–900 rpm (median 900, 3 tunes) | 675–1000 rpm (median 900, 15 tunes) | 600–925 rpm (median 850, 8 tunes) | 700–900 rpm (median 750, 4 tunes) |
| Warm idle airflow (in gear) | 8.6–13.6 g/s (median 12.1, 3 tunes) | 7.1–17.9 g/s (median 13.9, 15 tunes) | 7.0–13.7 g/s (median 12.2, 8 tunes) | 9.6–11.6 g/s (median 10.2, 4 tunes) |
| Idle spark (Gen IV, 800 rpm) | — | — | 13–19 ° (median 18, 8 tunes) | 16–17 ° (median 16, 4 tunes) |
| PE lambda | 0.85–0.85 (median 0.85, 3 tunes) | 0.77–0.89 (median 0.85, 15 tunes) | 0.83–0.89 (median 0.85, 8 tunes) | 0.85–0.85 (median 0.85, 4 tunes) |
| WOT spark, 5,000 rpm, about 0.9 g/cyl | 15.8–27.0 ° (median 21.6, 3 tunes) | 6.9–20.4 ° (median 14.4, 15 tunes) | 10.0–25.0 ° (median 19.5, 8 tunes) | 15.0–17.0 ° (median 15.0, 4 tunes) |
Tools in this hub
Turn-on tune sheet
The values to start with for your computer, induction, fuel and cam.
What does my tune need?
The checklist of everything your swap's tune has to handle.
HP Tuners, step by step
58 steps: the tables, what to log, the targets and when to stop.
Don't blow it up
Our safe limits and the checks before any wide-open pass.