Octane Questions Regarding Your Mods & Engine...

[Straight Success]

I'm working on my third CB, which to say the least, this is my keeper. However, I've read in the Accord manual that the recommended octane grating for the F22 is 87. Now, a few years back I had a stock '93. After months of experimenting, I notice that 93 octane made that car run the best, and provided me with the best MPG. Same scenario happened when I purchased my black '93 EX coupe.

Now I have a stock green '93 EX coupe, and since I started driving it, I again put 93 octane follow the trend of what seemed best. However, my car is being driven to school everyday with the stock F22, waiting for the semester to end to obtain my H. Never-the-less, it has been running horribly.

This morning the tank was on empty, so I decided to get a little gas. Instead of filling her up, I figured I would experiment with some 87. To my surprise, she took off and was purring. Way better performance, but I don't know what MPG's are going to look like.

My question is which octane do you use, is your car stock or modified (include mods if possible), and what type of MPG's do you get?

[mndude07]

Your experiences aren't consistent with the effects of different RON fuels on the same engine with such a low compression ratio. It seems like it was a "bad gas" experience or something along those lines. Basically for a stock or even bolt-on modified, un-tuned f22a, the fuel octane rating shouldn't matter.

My F22A1 in my 92 DX, with 87 octane, automatic(swapped to 5 spd later), A6 intake runners, H23 plenum, AEM short ram, axle back exhaust, and simple NGK V-power plugs, got 31.8 MPG on the highway averaging 65mph over a 115 mile trip, about 5-10 of which were stop-and-go traffic. This was with the A/C on the whole time, no cruise control at all.

[Straight Success]

Your experiences aren't consistent with the effects of different RON fuels on the same engine with such a low compression ratio. It seems like it was a "bad gas" experience or something along those lines. Basically for a stock or even bolt-on modified, un-tuned f22a, the fuel octane rating shouldn't matter.

My F22A1 in my 92 DX, with 87 octane, automatic(swapped to 5 spd later), A6 intake runners, H23 plenum, AEM short ram, axle back exhaust, and simple NGK V-power plugs, got 31.8 MPG on the highway averaging 65mph over a 115 mile trip, about 5-10 of which were stop-and-go traffic. This was with the A/C on the whole time, no cruise control at all.

The octane rating does matter. You can notice the difference in MPG between 87 and 93. I averaged about 3-5 more MPG on the highway alone and about 2-3 in the city (on my '93 SE). Performance wise, it offers not that much of a difference because as you stated the such low compression of our motors.

Now, my engine is running horribly, getting about 10 MPGs city. There's tons of problems, and I don't have time to trouble shoot everything as I'm preparing for an H swap (damn bills keep getting on my nerves too, killing my pockets and bank account). I'm assuming EGR needs to be cleaned, one or more injectors may inoperable or poorly functioning, maybe fuel filter needs replacing, and some other things. I recently did a basic tune up, and it offered no real improvement. I know the timing belt and WP is on it's way, and the cooling system needs to be flushed and spruced up. It bogs when I come off the clutch badly, but at least I can still feel the butterflies open at 4K or so.

She runs, but not good. I have to hash out a lot of money to get her at least up to par.

[Straight Success]

I may have some vacuum issues too.

[Tippey764]

I voted E85

[accordztech]

Stick with stock. Higher octane is for higher compressing numbers. Putting that into a lower compression car will be hurting the engine with more unburnt fuel. Octane rating is it's resistance to engine knock. The higher the octane the more energy required to burn it.

[almostJDM]

most of the country has under 93 octane so I use 91 but I voted 93 since its the closest higher rating

[mtnbikaah]

87 octane in both the sedan and wagon, both are stock.

5spd ex sedan: 33mpg.
5spd ex wagon: 27mpg. (need a tuneup BADLY, and better tires)

[steelbluesleepR]

The octane rating does matter. You can notice the difference in MPG between 87 and 93.

all else being equal, you will not see a difference in efficiency. that isnt how gasoline works. you may have that experience because of the improved additives and better quality of gas offered by specific stations, but it is not because of the octane level.

oh and e85 is a joke. it is 25% less efficient than gasoline and it is raising food prices for americans.

[texasvtak]

93 because the prelude manual says so.

edit: and i get 27/36

[GeoffM]

I voted E85

x2

[islandhopper]

...oh and e85 is a joke. it is 25% less efficient than gasoline and it is raising food prices for americans...

x2

[wed3k]

Stick with stock. Higher octane is for higher compressing numbers. Putting that into a lower compression car will be hurting the engine with more unburnt fuel. Octane rating is it's resistance to engine knock. The higher the octane the more energy required to burn it.

unburnt fuel is good for nox numbers, but if you dont see an advantage with higher octane, i personally would save the money unless one is trying to pass smog. (if that was the case, id get the street legal 100 octane)

but always 87 in a stock honda and it always got around 30mpg and 34 all highway.

[EJX_Michael]

93-91 octane is sold around here. I have to get 93 for the H.

Winter I got around 27 MPG. I expect 29+ with the summer blend of gas. I vtec 85% of the time I drive though.

[accordztech]

unburnt fuel is good for nox numbers, but if you dont see an advantage with higher octane, i personally would save the money unless one is trying to pass smog. (if that was the case, id get the street legal 100 octane)

but always 87 in a stock honda and it always got around 30mpg and 34 all highway.

Good for nox numbers but bad for hc numbers. I personally would retard the timing a bit to decrease nox if the hc numbers were decent

As for e85 its not that efficient. Also kinda dirty. A few Turbo guys ran them and they pulled their injectors a year later to find it all gummed more than if they used 93.