Honda Car Forum

I have a 2003 Civic Si and the dealer said to use premium fuel only. The manual says to use regular. Am I wasting money by using the 93 octane, or is it actually better for the vtec engine?

do what the manual says

I have owned dozens of cars over the years, both economical and high performance. The manual says to use regular and that is fine, but I have always put a tank of high test through my engines from time to time and can notice a difference in idling and performance. Try filling up with a high octane and detergent gasoline after every four or five tanks.I would also suggest you use Synthetic oil in your engine. Set the date and mileage for 5,000 miles or five months. It is a little more expensive but better for your engine. Plus, you get another 2,000 miles. It does not break down like regular oil.

I doubt you will get full power and can dammage your engine using any thing less than the very best octane. Read the manual carefully it probably says 89 roz iron for the regular Civic or something you don't understand properly. The Civic SI uses 10 to one compression to make over 200 hp. Get used to premium fuel only. Pinging from low octake will shorten your valve life and possably dammage pistons.

Actually the dealer is right!The civic si engine in 2003 has a compression ratio of 9.8 to 1.Your gonna need at least 91 octane fuel.Your engine is not going to die from lower octane fuel,it will adapt to the fuel by way of retarding the timing to reduce pre-detonation.This will give it slightly less in the performance department.

The civic si power output ratings are while using premium fuel 93 octane rating or higher, the car can run on regular but you will not get optimal performance. As for other readers regular gas cars like the original civics don't gain performance with octane.

Actually, the car requires 91 octane or better. Any less will rob performance. Anything more would be best. In California you will not find anything better.

mid grade like 89 so it wont run rich

use regular, i have a 2007 si which according to the owners manual requires min 91 octane, maybe thats why the dealer said use premium?