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Hmmmm, where is the timing set so to use 87 octane without pinging?

Bill
Constantly changing along with valve timing and injector timing/rate as managed by the sophisticated ECU, detonation / knock sensors, load demand sensors, etc, etc.

Old rules of thumb linking particular octane values, compression ratios, and detonation no longer apply even on NA engines. Flame propagation and detonation can be managed to an amazing degree with the very precise injectors used these days. But yes, ultimately there are octane-related limits to timing advance, all else being equal.

Note, too, that the published 11.5:1 is likely a maximum volumetric calculation; by virtue of variable valve timing the cylinders may not experience that at any given instant in time.
 

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Constantly changing along with valve timing and injector timing/rate as managed by the sophisticated ECU, detonation / knock sensors, load demand sensors, etc, etc.

Old rules of thumb linking particular octane values, compression ratios, and detonation no longer apply even on NA engines. Flame propagation and detonation can be managed to an amazing degree with the very precise injectors used these days. But yes, ultimately there are octane-related limits to timing advance, all else being equal.
Yep, just thinking back to the old school where we didn't want to run much higher than maybe 9.0:1 without running premium to keep from pinging, so just trying to wrap my head around getting full HP from 11.5:1 on only 87 octane??

Bill
 

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Yep, just thinking back to the old school where we didn't want to run much higher than maybe 9.0:1 without running premium to keep from pinging, so just trying to wrap my head around getting full HP from 11.5:1 on only 87 octane??

Bill
For comparison we have a Lexus GX460 with a smallish v8 and a 10.2 compression ratio that requires premium.
 

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The MDX is tuned to run on premium, and will retard timing in the event lower octane is used. The RL is tuned for 87, and I don't think it advances timing enough to make any considerable HP increase if you use 91 or 93. If it does, it's probably all the way at the top of the RPM range. As for a MPG increase, I doubt it's enough to warrant the 20% higher price of premium.
 

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Old rules of thumb linking particular octane values, compression ratios, and detonation no longer apply even on NA engines. Flame propagation and detonation can be managed to an amazing degree with the very precise injectors used these days.
Indeed. The 2.0L direct-injected engine in the Miata has a CR of 13:1 and can run on 87 without damage. It uses an injection strategy that sprays fuel into the cylinder up to three times per compression stroke to create a richer mixture around the spark plug and a more consistent mixture in the rest of the cylinder. At the 7,500 RPM redline, that's 188 injections per second which blows my mind.
 

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Engines generally run fine on lower octane at higher elevations so I don't know why Honda would say that you might want to use higher octane at higher elevations, but zroger73 knows almost everything about these so I can't argue with him on Honda's recommendation. The computers in modern engines can usually adjust to accomodate different octanes which the old engines couldn't do. In at least some areas, 85 octane does not have ethanol while higher octane does. That said, when I tried 85 octane at high elevation in my G1 it generally worked but I got a bit of knocking up steep hills so I went back to 87 at all altitudes, and that's what I've done in my G2 also. Two nights ago I pulled a trailer, with truck & trailer fairly well loaded, over the Sierras (highest pass, 7239 ft.), with temperatures ranging from about 20-30 degrees, using 87 octane, and I had no knocking and seemed to have plenty of power to go up hills at or above the speed limit.
 

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Just got our RTL AWD a couple weeks ago, are headed into the mountains for a short trip next week, and just wondering if 89, 91, 93 octane gas is useful for that type of driving, or for everyday use for that matter.

Searched "octane" here and saw mostly G1-related comments and some G2 comments that were a couple years back, and not a lot of actual experience G2-wise.(could be that I'm not an adept "searcher"), so thought I'd ask at this point in history, with many more G2s on the road/owner experiences in the ROC mix.
Using 93 will get you 10 more horsepower. Otherwise, 87 is fine. On a long trip I usually run two or three tank fulls to keep the engine clean. Exon 93 has extra cleaners in it.
 

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Using 93 will get you 10 more horsepower. Otherwise, 87 is fine. On a long trip I usually run two or three tank fulls to keep the engine clean. Exon 93 has extra cleaners in it.
Thanks for the info. I think Exxon is prominent where we're going - can likely get that.
 

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FWIW, 87 octane fuel actually packs more energy, i.e. produces a more explosive flame front than the higher octanes. Detonation and/or preignition is the likely result in high compression non-computerized vehicles under a load, with the accompanying power loss. High octanes produce a slower flame front and was necessary in that regard in the old vehicles. In my modern Toyota I've seen a slight mpg increase with higher octanes but that is offset by the price increase. Haven't tried it in the G2.
 

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FWIW, 87 octane fuel actually packs more energy, i.e. produces a more explosive flame front than the higher octanes. Detonation and/or preignition is the likely result in high compression non-computerized vehicles under a load, with the accompanying power loss. High octanes produce a slower flame front and was necessary in that regard in the old vehicles. In my modern Toyota I've seen a slight mpg increase with higher octanes but that is offset by the price increase. Haven't tried it in the G2.
That's not correct. There is no difference in energy content between 87 and 91 octane gasoline. The difference is that higher octane fuel is simply more resistant to compression-ignition. It doesn't burn any slower or faster. Fuel that is more resistant to compression-ignition can be compressed more without igniting prematurely on its on instead of when spark occurs.
 

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That's not correct. There is no difference in energy content between 87 and 91 octane gasoline. The difference is that higher octane fuel is simply more resistant to compression-ignition. It doesn't burn any slower or faster. Fuel that is more resistant to compression-ignition can be compressed more without igniting prematurely on its on instead of when spark occurs.
Higher octanes actually produce a slower flame front.
 

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Higher octanes actually produce a slower flame front.
 

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Extremely technical article that ends with "Flame speed does not correlate with octane."

The article was posted in 2007 which should not impact the accuracy of fuel chemistry description, but could have additional observations today when Direct Injection engines make up the majority of engines in the automobile industry.
 

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I just took my 2019 on a trip and tested this. I actually had the same mileage with 93 octane as I had with 87 octane. The only way I was able to improve the mileage was too add 1oz of 100% acetone per quarter tank I was filling. At $.99 for 6oz from Walmart, the mileage increase, average 4mpg, did make the expenditure worth it. However, I've heard that using acetone on around the town daily mileage doesn't help, especially in the summer, because it evaporates too quickly. So I'd only recommend it on trips where you will be using a minimum of a half a tank in one drive.
 

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I just took my 2019 on a trip and tested this. I actually had the same mileage with 93 octane as I had with 87 octane. The only way I was able to improve the mileage was too add 1oz of 100% acetone per quarter tank I was filling. At $.99 for 6oz from Walmart, the mileage increase, average 4mpg, did make the expenditure worth it. However, I've heard that using acetone on around the town daily mileage doesn't help, especially in the summer, because it evaporates too quickly. So I'd only recommend it on trips where you will be using a minimum of a half a tank in one drive.
Funny.

For everyone else, don't fall for this urban legend. NEVER pour ACETONE in your fuel tank!



 
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