Introduction
Power figures get thrown around in tuning like confetti. “Stage 1 = 220 hp.” “Stage 2 = 270 hp.” But without airflow data, those numbers are just optimistic storytelling.
There is a simple physical truth sitting underneath every combustion engine:
Air in = fuel burned = power out.
That’s why MAF g/s (grams per second of airflow) is one of the most honest indicators of real engine output. Once you understand the relationship between airflow and horsepower, you can instantly tell whether a claimed power figure is realistic, exaggerated, or hiding a mechanical issue.
This guide explains the airflow-to-power rule-of-thumb, how it differs for diesel and petrol engines, and how to use it to validate remaps and diagnose underperforming vehicles.
Why Airflow Defines Power
Engines are air pumps.
Fuel is only there to release the energy stored in oxygen.
If airflow is restricted:
• You cannot burn more fuel
• You cannot make more power
• No map can change that
This is why two cars with identical boost pressure can make very different power — boost is pressure, MAF is mass. Mass is what matters.
The Diesel Rule-of-Thumb
For modern turbo diesel engines:
≈ 0.8 to 1.0 horsepower per gram/second of MAF airflow
Real-world examples:
• 180 g/s ≈ ~170–180 hp
• 220 g/s ≈ ~210–220 hp
• 260 g/s ≈ ~250–260 hp
• 300 g/s ≈ ~290–300 hp
This rule is surprisingly accurate for common-rail turbo diesels in Stage 1–2 territory.
If someone claims:
“Your car makes 260 hp”
…but your log shows:
215 g/s
You already know something is off.
The Petrol Rule-of-Thumb
Petrol engines need slightly more airflow per horsepower due to different combustion efficiency.
Typical range:
≈ 1.1 to 1.3 g/s per horsepower
Examples:
• 200 g/s ≈ ~155–180 hp
• 250 g/s ≈ ~190–220 hp
• 300 g/s ≈ ~230–270 hp
Turbo petrol engines with good intercooling and high VE sit toward the better end of this range.
Why This Beats Dyno Claims
Dyno figures vary wildly due to:
• Tyre slip
• Strapping differences
• Gear selection
• Correction factors
• Weather
MAF g/s doesn’t care about any of that.
It is measuring actual air mass entering the engine in real driving conditions.
That makes it:
• Repeatable
• Comparable
• Immune to marketing optimism
Using Airflow to Validate a Remap
Before tuning:
• Log stock MAF g/s peak
After tuning:
• Log tuned MAF g/s peak
Example:
Stock: 185 g/s
Tuned: 235 g/s
You’ve gained ~50 g/s airflow.
That translates to roughly ~45–55 real horsepower increase on a diesel.
No guesswork. No inflated graphs. Just physics.
Diagnosing Underperforming Cars
If a car is mapped for “230 hp” but logs only 190 g/s:
Possible causes:
• Boost leak
• Clogged intercooler
• Weak turbo
• Intake restriction
• EGR stuck open
• Exhaust restriction
• Poor remap limiting airflow
Airflow reveals the truth immediately.
Why Boost Alone Misleads Again
Two cars both showing “1.6 bar boost”:
Car A: 240 g/s
Car B: 200 g/s
Same boost. Very different air mass.
Car B is either restricted or badly calibrated.
This is why professional tuners always look at MAF, not just MAP.
Practical Example
A 2.0 TDI logs:
• Peak boost: 1.55 bar
• Peak MAF: 210 g/s
Expected real power:
≈ 200–210 hp
If a dyno sheet claims 240 hp, the dyno is lying — not the MAF.
The Takeaway
Once you understand airflow-to-power relationships:
• You can sanity-check any power claim
• You can validate tuning results
• You can diagnose hidden airflow faults
• You stop relying on marketing numbers
It’s one of the simplest but most powerful tools in real-world performance diagnostics.
Want Your Logs Checked?
If you’re unsure whether your vehicle is delivering real power or just optimistic dyno numbers, we offer log analysis and health checks alongside our tuning services. Send your MAF log and we’ll tell you exactly where your engine stands.