I always put premium in my b16 civic but I have a half tank of mid grade in there now. I want to go and rip it.... Is it really bad to vtec it with that grade gas in it? Never tried it.... is it going to have detonation issues?

 

According to the Civic Si owners manual, premium (91-93 octane) is recommended but the engine will still run fine on 87 or 89 octane because the ECU can retard timing as necessary. However, it also says to expect loss in performance and loss in gas mileage while using a grade of gasoline other than premium. Since the manual says it is fine, I would assume that the statement includes using being able to use the entire factory-intended powerband without consequence.


Also, unless your tank was nearly dry when you filled up with 89 octane, the gas in your tank is probably slightly more than 89 octane due to the old gas mixing with the new gas.

 

you will probably be fine, why the change in octane though?

 

Mid-grade in Wisconsin is 91, which is what the owner's manual considers Premium. You'll notice some very slight hesitation, or a very slight power loss with the more throttle you give it. You won't run into any issues if you're still running a knock sensor, unless you have 12:1 pistons in there and tons of headwork.

Long story short, it's fine.

 

I have no idea why I decided to buy it, I thought I was going to see if I noticed the difference, i thought no way in hell will I notice it but I did slightly.

 

dam. thanks for letting me learn from your mistake ha

 

I run 89 in mine all the time and notice no performance or mileage difference between 89 and 91.

It's not going to hurt it if you have a knock sensor. B16s don't run *that* high of compression stock.

 

haha. so its probably bad that i put 87 into a gsr then. whoops.

reasoning?: gas = expensive

 

89 here all day, all long... lol