HP Tuners Cammed LS/LT Idle Tuning: Base Running Airflow & Idle Speed Guide
One of the first problems many tuners encounter after installing a larger camshaft in an LS or LT engine is getting the vehicle to idle consistently and recover correctly.
The engine may start and run, but then you begin dealing with problems like poor idle quality, stalling, or an idle that simply doesn't behave the way you want.
One of the areas you need to understand when correcting these problems is Base Running Airflow (BRAF).
So how much Base Running Airflow does a cammed LS or LT actually need?
There isn't one number that works for every combination, but there are some useful starting points that can get you much closer.
In this guide, I'll cover starting values for idle speed, warm Base Running Airflow, and idle spark for several common Gen 3, Gen 4, and Gen 5 camshaft combinations.
What Is Base Running Airflow?
Base Running Airflow is an important part of the airflow strategy used to keep the engine running at the desired idle speed.
Once you install a larger camshaft, the airflow requirements of the engine can change considerably.
The engine may require additional airflow to maintain a stable idle compared with the original stock calibration.
This is why simply installing a camshaft and leaving the factory idle airflow calibration untouched may not produce the idle quality you're looking for.
Why Does a Cammed LS/LT Need More Idle Airflow?
A larger camshaft changes how the engine behaves at idle.
Different camshaft combinations can require different amounts of airflow, which is why there isn't one universal BRAF value you can copy into every tune.
Engine size and vehicle configuration also matter.
A larger-displacement engine will generally require more airflow, and an automatic-transmission vehicle will generally require more airflow than a comparable manual-transmission combination.
The goal is to provide the engine with an appropriate starting amount of airflow and then refine it for the actual vehicle.
Gen 3 LS Base Running Airflow Starting Points
Here are some starting points I use for common Gen 3 combinations.
Gen 3 – Truck Norris
Park/Neutral Idle: 750 RPM
Drive Idle: 750 RPM
Warm BRAF: 8.5–9.5 g/sec
Gen 3 – Stage 3 Truck Cam
Park/Neutral Idle: 800 RPM
Drive Idle: 750 RPM
Warm BRAF: 10.0–11.5 g/sec
Gen 3 – BTR 400 Stroker
Park/Neutral Idle: 950 RPM
Drive Idle: 950 RPM
Warm BRAF: 14.0–17.0 g/sec
Gen 3 – TSP F35
Park/Neutral Idle: 950 RPM
Drive Idle: 950 RPM
Warm BRAF: 14.0–17.0 g/sec
Notice how dramatically the airflow requirement can increase as the combination becomes more aggressive.
This is exactly why copying a BRAF value from an unrelated tune isn't always a good approach.
Gen 4 LS Base Running Airflow Starting Points
Gen 4 – Truck Norris
Park/Neutral Idle: 800 RPM
Drive Idle: 750 RPM
Warm BRAF: 7.5–8.5 g/sec
Gen 4 – Stage 3 Truck Cam
Park/Neutral Idle: 775 RPM
Drive Idle: 750 RPM
Warm BRAF: 9.0–10.5 g/sec
Gen 4 – BTR 220
Park/Neutral Idle: 800 RPM
Drive Idle: 750 RPM
Warm BRAF: 10.5–12.0 g/sec
Gen 4 – BTR 225
Park/Neutral Idle: 825 RPM
Drive Idle: 775 RPM
Warm BRAF: 12.0–13.5 g/sec
Again, these values aren't meant to be copied blindly.
They're intended to give you a reasonable place to begin before refining the calibration for the actual engine.
Gen 5 LT Base Running Airflow Starting Points
Gen 5 applications need to be treated differently from earlier LS combinations.
The airflow values below are useful starting points, but they do not include the additional virtual torque tuning considerations involved with Gen 5 applications.
Gen 5 – Truck Norris
Park/Neutral Idle: 750 RPM
Drive Idle: 750 RPM
Warm BRAF: 6.5–7.5 g/sec
Gen 5 – Stage 3 Truck Cam
Park/Neutral Idle: 750 RPM
Drive Idle: 750 RPM
Warm BRAF: 8.5–10.0 g/sec
Gen 5 – BTR 220
Park/Neutral Idle: 775 RPM
Drive Idle: 750 RPM
Warm BRAF: 9.5–11.0 g/sec
Gen 5 – BTR 225
Park/Neutral Idle: 850 RPM
Drive Idle: 800 RPM
Warm BRAF: 11.0–12.5 g/sec
One thing worth noticing is that you shouldn't assume a Gen 3, Gen 4, and Gen 5 engine with a similar camshaft will automatically require the exact same BRAF value.
Treat each platform and combination accordingly.
What About Idle Spark?
Airflow is only one part of getting a cammed engine to idle correctly.
Idle spark is another important part of the equation.
Here are some useful warm idle spark starting points for several common camshaft combinations:
Truck Norris
18–22°
Stage 3 Truck
20–24°
BTR 220
22–26°
BTR 225
24–28°
As the camshaft becomes more aggressive, you can see that the starting idle spark recommendation generally increases.
But just like BRAF, these numbers aren't meant to replace datalogging and calibration.
Get the Fueling Right First
This is one of the most important parts of the process:
Fueling needs to be dialed in before you finalize the airflow requirements of a cammed engine.
If your fueling is significantly incorrect, you can end up making airflow changes in an attempt to compensate for a different problem.
That can send you in the wrong direction.
Get the fueling where it needs to be, then refine the idle airflow calibration.
Why Your Engine May Need More Airflow Than These Numbers
These values are starting points.
Several factors can increase the amount of airflow your specific engine needs.
Air Conditioning
When the A/C compressor adds load to the engine, additional airflow may be required to maintain the desired idle.
Electrical Load
Higher electrical demand can also increase the engine's idle load and airflow requirement.
Engine Displacement
Larger engines generally require more airflow.
This is one reason you shouldn't automatically copy a value from a smaller engine into a larger-displacement combination.
Automatic vs. Manual Transmission
Automatic-transmission combinations generally require more airflow than manual-transmission vehicles.
The engine needs to deal with the additional load placed on it when the transmission is in gear.
Don't Just Keep Adding Airflow
A common mistake when dealing with a poor idle is assuming that every problem means the engine needs more Base Running Airflow.
It doesn't.
BRAF is only one part of the overall calibration.
Before continually adding airflow, make sure you've addressed the other parts of the combination—especially fueling.
If you keep adding airflow to compensate for another calibration problem, you can create additional idle-control issues instead of fixing the original problem.
A Note About Gen 5 LT Tuning
With Gen 5 applications, don't look at these BRAF values as the entire solution.
The values in this guide do not include virtual torque tuning.
Gen 5 idle behavior has to be considered as part of the larger torque-based control strategy.
That means you shouldn't expect to simply enter a BRAF number and have every cammed Gen 5 vehicle immediately behave correctly.
Use the airflow number as a starting point and tune the complete strategy.
GCT Rule of Thumb
When you're trying to establish a base calibration for a cammed LS or LT:
Get the fueling right first.
Then establish a reasonable idle speed and Base Running Airflow starting point for the engine and camshaft combination.
From there, evaluate how the engine behaves and make changes based on the actual vehicle.
Remember:
A/C and electrical load can increase airflow requirements.
Larger engines generally need more airflow.
Automatics generally need more airflow than manuals.
More aggressive camshafts can require substantially different airflow and idle-speed targets.
Gen 5 applications require additional consideration of the virtual torque strategy.
Don't chase someone else's BRAF number.
Use it as a starting point and let the engine tell you where it needs to be.
The Key Takeaway
There isn't one perfect Base Running Airflow number for every cammed LS or LT engine.
A mild Gen 5 truck cam may need considerably less warm airflow than an aggressive Gen 3 stroker combination.
That's why understanding the combination matters.
Use these BRAF, idle RPM, and idle spark recommendations to get yourself into a reasonable starting range.
Then verify fueling, datalog the vehicle, account for engine and accessory loads, and refine the calibration until the engine behaves correctly.
The goal isn't to hit a specific BRAF number. The goal is to get the engine to idle and behave the way it should.
Want to Learn How to Tune Cammed LS & LT Engines?
If you want to understand how to properly dial in idle airflow instead of guessing at Base Running Airflow numbers, check out the Gulf Coast Tuning and Calibration GM LS/LT Master Tuning Course.
Learn how to approach idle, airflow, fueling, spark, torque management, transmission tuning, and complete modified GM combinations using HP Tuners.
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