Best MPG Tracking Apps for Monitoring HHO Results in 2025

Why App-Based Tracking is More Accurate

The vehicle's built-in MPG display is often optimistic (some studies show 3–8% higher than actual). Apps based on fill-up data calculate actual MPG using gallons purchased and miles driven — the most accurate method available without laboratory equipment.

Fuelly (iOS/Android — Free)

Fuelly is the most popular fuel economy tracking app, with a large community database for comparison. Log each fill-up with gallons and odometer reading. The app calculates tank MPG, running average, and graphs trends over time. Essential for documenting before/after HHO results with proper statistical significance.

GasCubby (iOS)

More detailed than Fuelly with expense tracking, maintenance logs, and cost-per-mile calculations. Ideal for HHO owners wanting to track not just MPG but total cost-of-ownership impact including system investment.

Torque Pro + OBD-II (Android)

Torque Pro connected to a Bluetooth OBD adapter provides real-time MPG calculation from fuel injector duty cycle data. More sensitive to short-term HHO effects than fill-up based apps. Best for tuning sessions where you need immediate feedback on EFIE adjustments.

Methodology for HHO Testing

• Log minimum 5 fill-ups before HHO installation (baseline)
• Drive the same routes as baseline during testing period
• Allow 3 fill-ups after installation before comparing (ECU relearning period)
• Compare 5+ fill-ups after installation to 5+ before
• Control for season: summer vs winter comparison is invalid