Octane Use Poll - Page 3 - 10th Gen Civic Forum
View Poll Results: What octane are you using in your 10th Gen?
87 32 66.67%
89 6 12.50%
91 6 12.50%
93 4 8.33%
Voters: 48. You may not vote on this poll

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post #21 of 33 (permalink) Old 10-22-2016, 03:58 PM
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I'm going to gamble and run 89 octane, just for a bit more margin of error. Everything in the manual says 87 or higher, and going below 87 could be harmful. So it doesn't say higher octane isn't necessary just that it needs a minimum of 87. Our compression ratio is relatively high for 16 lbs boost, so a bit more octane could be a benefit. Modern engines all run on the cusp of detonation by advancing and retarding ignition timing, and our engines will manipulate valve timing too. I think running a bit more octane may result in ignition timing staying higher and more consistent. I can monitor ignition timing advance with my scangauage which I may do over the next while. It may not benefit from 91 but a couple more points may be helpful. The extra cost isn't that much for 89 and if I'm wrong it isn't a large amount. I'll try it for a couple of tanks and monitor it.

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Last edited by JS2000; 10-22-2016 at 06:18 PM.
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post #22 of 33 (permalink) Old 10-22-2016, 05:57 PM
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Someone remind me what the compression ratio is again ? But in to see you're results on what you find. If the manual calls for 87 octane, I'm sure it's good enough. But if you want to bump to 89 octane for safe measures, heck, why not. Let's see if you find anything different enough ?
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post #23 of 33 (permalink) Old 10-22-2016, 08:36 PM
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Quote:
Originally Posted by High Mileage View Post
The purpose of higher octane fuel is to prevent pre-ignition (knocking) caused by high compression ratios. That's it folks. Unless you are running a high compression engine, such as a Corvette, it is not necessary and a waste. The Civic does not have a high compression ratio engine. Regular and Premium explode with equal intensity when sparked off with the engine's spark plug. One is not more 'powerful' a fuel than the other. However, Premium is engineered to resist ignition simply by being compressed.
The first part of this statement is correct, but that's not it folks. In every study I have read on this subject everyone agrees that you also get a slower, better controlled, and more complete burn with a higher octane and this, depending on the individual vehicle, may or may not improve fuel economy and power or in some cases may make it worse.

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post #24 of 33 (permalink) Old 10-22-2016, 08:59 PM
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Originally Posted by Cabeldude View Post
The first part of this statement is correct, but that's not it folks. In every study I have read on this subject everyone agrees that you also get a slower, better controlled, and more complete burn with a higher octane and this, depending on the individual vehicle, may or may not improve fuel economy and power or in some cases may make it worse.
That's true, so there isn't any single general statement that can be made about octane vs. power, and cars like Corvettes are not the only vehicles that maximize performance based on octane levels.

In a modern turbocharged car it depends on how the vehicle's ECM controls ignition timing, valve timing, and boost vs. knock detection readings, and how sensitive that relationship is. If you run higher octane and the ECM keeps ignition timing advance, and boost set higher due to reduced knock then the engine will make more power. Conversely, if the ECM doesn't detect knock on lower octane fuel and it doesn't retard ignition timing or boost then it can make just as much power on lower octane fuel.

I think with a compression ratio of 10.6 and boost reaching up to 16 lbs our ECM's will be sensitive to knock readings, and will adjust timing and boost accordingly on the fly. It's a very seamless process which can't be detected by the driver but it can affect power and fuel economy, timing and boost maps can be constantly changing. Always worth exploring octane levels IMO.


I know that I can dump 87 octane into my S2000 which normally takes 91 octane. It will run perfectly safe, but performance will decrease as ignition timing will be retarded by the ECM, much like it does with high intake temps and high coolant temps. My old Dodge SRT-4's would behave the same way, very much dependant on how the ECM adjusts performance based on sensor readings.


I hope to toss on an intake in the next few weeks so a bit more octane could work well with leaner air fuel ratios. Just a guess and I'll try to track the engine performance along the way.

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Last edited by JS2000; 10-22-2016 at 11:08 PM.
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post #25 of 33 (permalink) Old 10-23-2016, 03:04 PM
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Tried top tier 91 yesterday,but really a waste of money as it runs the same on 87.I did get 42.3 MPG @75 MPH on a drive from Osceola IA to Ames IA yesterday on the 91 octane but have not compared to 87.
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post #26 of 33 (permalink) Old 10-23-2016, 04:43 PM
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Originally Posted by Deathklok View Post
Tried top tier 91 yesterday,but really a waste of money as it runs the same on 87.I did get 42.3 MPG @75 MPH on a drive from Osceola IA to Ames IA yesterday on the 91 octane but have not compared to 87.
I think it takes a couple tanks of any fuel to find consistent performance. Top tier 91 also contains higher levels of cleaning additives, which might be good for our high pressure direct injectors, 87 always has lower levels of additives. I think 89 might be a good happy medium but I don't have any proof of it. Your fuel economy numbers sound good.


Thanks for sharing your info.

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post #27 of 33 (permalink) Old 10-30-2016, 02:55 PM
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You guys can always just buy additives and cleaners to run through the system every so often since on a tank by tank basis it can really add up. But at the end of the day its really up to you. As far as I understand new vehicles don't require any of this stuff for a very long time.
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post #28 of 33 (permalink) Old 11-01-2016, 08:15 PM
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I use Non-Ethanol 89. Seems to do just fine in the civic touring 1.5liter.

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post #29 of 33 (permalink) Old 11-02-2016, 03:32 PM
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you have non-ethanol at that octane? our lowest pure-gas here is 91....and yes, it's by far the most expensive...

and after 55k miles (remember, i'm in a 9th gen), i'm getting far better mileage with the non-ethanol gas. is it worth the money...who knows...probably not...but, seeing 48.8 on the i-mid this morning in rush hour, 21 miles into commute isn't' something to disregard.

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post #30 of 33 (permalink) Old 11-02-2016, 08:08 PM
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Yes,
89 Non-ethanol. There was 93 non-ethanol in my local area and then they dropped it down to 89 (Stated it was harder to get the 93). I will continue to run this as well...I don't see an issue with it.
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