I recently went to a full service station and the attendant
"accidentally" put low octane in the tank. I didn't notice until I pulled away and looked at my receipt. Consequently, I didn't notice any decrease in performance but have made a promise to myself to watch the attendants more closely.

 

I've been using 91 for a few tanks now and haven't really noticed a difference in gas mileage or performance. Not sure if 1 octane is really going to make that much difference.

By the way, I've been talking to Da Hapa about this issue, since he works in the accounting dept. of a gas manufacturer. He told me that they might go back to 92, after all the reformulation stuff in CA is over (getting rid of MTBE). We might get our 92 back, but it's not a guarantee.

Also, as far as adding octane boost, I was told that it's a waste of money. The amount of octane boost you put in to a full tank of gas is too little to actually raise the octane in the car. The better way to raise the octane is the way Moneeb is doing it, by actually mixing a higher grade.

 

So, the only time to need higher octane is when the weather is hot? Also, what about the Mugen ECU... why does it need higher octane?

 

I use Sunoco Ultra 94 with a +4 points octane booster every other fill-up and it seems to suit my car just fine. All I can add to this ongoing octane debate is my personal experience when going from 94 to 91. For a tank or two, I don't notice any difference but if I keep the 91 in my car for more than 100 city miles, it seems like the car loses a bit of its responsive when getting off the line, even with moderate rpm starts...say 3K. The car just seems to bog easier. When I notice this, I'll run the car down to one bar and run up a 1/2 tank full of my 94 + 4 nectar. Within 25 miles, that hesitation off the line at 3K seems to disappear. I certainly have no scientific or mechanical engineering background to explain why this is but it is definitely noticeable.

 

Russ, gorgeous kitty! You should be proud.

 

I don't know the exact details on the Mugen ECU, but I'm assuming it advances your ingition timing, and probably trims back your fuel delivery in the high rpms, to make a few more hp. When the ECU does this, it's increasing your chances for pre-ignition or detonation. A higher octane fuel will help to reduce your chances of detonation.

To the original question about 93 making more power than 91, under normal circumstances I'd say no. But, the ECU will compensate how much timing it pulls based on the fuel's octane rating. This might cause you to lose a few horsepower when it's hot out and the ECU is really pulling some timing. Also, the higher octane fuel might not detonate when the 91 would, so the knock sensor would never hear anything, and therefore never pull timing and dump fuel to avoid an engine catastrophe.

 

Can you mix leaded fuel with unleaded?

 

This is what I read in Car & Driver several years ago. Detonation is the whole point. It's not a power issue at all.

 

In a report that was published following the S2000 owner's tour of the manufacturing facilities in Japan, one of the Honda engineers was quoted as saying "Engine tuning differences world wide were done to match up the the differences in octane ratings of gasoline. Japan is 100, Europe is 98, and the US is 95."

 

But if the engine doesn't have detonation problems, what's the use of the higher octane?