Do Civic Si require premium gas?

Yes. Honda specifies premium unleaded gasoline with an octane rating of 91 or higher for the Civic Si to deliver its designed horsepower and turbocharged performance.

What the manufacturer recommends

Honda's owner’s manuals for recent Civic Si models consistently call for premium unleaded gasoline with an octane rating of 91 or higher. While the engine can run on lower-octane fuels, doing so may reduce power and throttle response as the engine management system adjusts timing to prevent knock.

The case for using premium gasoline

Premium gasoline is recommended for the Si to maintain peak performance, consistent turbo response, and to avoid timing-related detuning. Consider these factors:

• High-compression turbocharged 1.5-liter engine relies on higher octane to resist pre-ignition under boost.


• The engine management maps are calibrated for 91-octane (or higher) fuel to preserve horsepower and responsiveness.


• Using premium minimizes the risk of engine knock and ensures the turbocharger delivers power as intended during spirited driving.

In short, premium supports the Civic Si's design goals and protects engine performance during high-load operation. Regular gasoline may still run in a pinch, but you should expect reduced performance and quicker onset of timing adjustments.

What happens if you run regular gas

Running regular (87 octane) can trigger the engine's knock sensor when operating near the Si's boost levels. Expect reduced horsepower, slower acceleration, and altered throttle response as the ECU retards timing to prevent detonation. In some driving situations, you may also notice slightly higher engine temperatures and lower fuel economy. Repeated use of lower-octane fuel may lead to longer-term wear if the car is operated aggressively, though the car is designed to tolerate occasional use in emergencies.

Practical guidance for owners

If you own a Civic Si, plan to fill with premium for daily driving and spirited runs. In an emergency, you could use regular gasoline temporarily, but revert to premium as soon as possible to restore designed performance. Always follow your model-year owner's manual for octane requirements, and be mindful of any warnings or service advisories from Honda about octane use for your specific vehicle.

Model-year notes and regional variations

Across recent Civic Si models (roughly 2017 to present in the U.S.), Honda has maintained the premium-octane requirement. Some markets outside the U.S. may label octane differently (RON vs. MON) but the guidance remains premium gasoline as the preferred fuel for peak performance. Check your local manual or dealer if you’re in a different region or driving a new model year.

Summary

The Civic Si is designed to run on premium unleaded gasoline with an octane rating of 91 or higher. Using premium helps preserve horsepower, turbo response, and engine safety during high-load driving. Regular gasoline can be used in emergencies but will reduce performance and may trigger timing adjustments; for best performance and long-term reliability, stick to premium as Honda recommends.

Does the Civic SI use regular gas?

Honda engines are certified and designed to run on regular unleaded gasoline.

What gas does a 2026 Civic SI take?

Regular Unleaded
Civic Si Specifications

Does the Honda Civic take 87 or 89?

Use of unleaded gasoline of 87 octane or higher is recommended. Use of unleaded gasoline of 91 octane or higher is recommended. Honda recommends TOP TIER Detergent Gasoline where available. Do NOT use gasoline containing more than 15% ethanol.

What happens if I put 87 instead of 91?

If you put lower-octane fuel into your high-octane vehicle, whether by mistake or to save money on gas, you'll probably notice the effects right away: things like poor fuel economy, reduced acceleration, and spark knock, which sounds like a high-pitched pinging or rattling noise.