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Then learn how to understand English sentences. I didn't only say "doesn't do (EXPLOSIVE, PAINFUL, AND UNCONTROLLABLE BOUTS OF DIARRHEA WHICH WILL LEAD TO DEHYDRATION, HOSPITALIZATION, ORGAN FAILURE, REPEATED RESUSCITATION, EVENTUAL DEATH, LAWSUITS, ACCUSATIONS, ALLEGATIONS, ACCEPTANCE, LEGAL SETTLEMENTS, AND A YOUTUBE TRIBUTE VIDEO WITH 6 VIEWS)". There were qualifying sentences that followed. Read and try to comprehend. Like I said, this isn't rocket science.

My 1972 F100 will get absolutely zip from higher octane gas. Ditto my 1994 Suburban. Both rigs will burn it just fine but won't gain from it. If your Honda whatever has the ability to adjust the timing to get more power it will say so in the owners manual.
Hahaha I don’t know how all that got put in my post.. seriously, I didn’t put that there.

Okay... I understand what might or might not be in the damn owners manual. The fact is, that through testing on a dyno, there are proven gains. This has been testing by more than one source. I don’t understand your ignorance.

I know that your 72’ Ford doesn’t have and ECU capable of adjusting timing with different octane ratings. We are talking about a 2018 Honda Accord.
 

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I'm assuming you're aiming this at me. I didn't say it doesn't make a difference. I said it doesn't make a difference if your vehicle can't take advantage of it. I also said such information would be present in your owners manual and that you wouldn't have to waste time/effort/money/brainwaves "trying it."

OK are we good now?

One question for you. Do you get a gain in mpg running 93 octane?

Dude.. get it through your head.. you are posting in a 10th gen Honda Accord forum. It is proven this is possible with this car.

Just stop.
 

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Dude.. get it through your head.. you are posting in a 10th gen Honda Accord forum. It is proven this is possible with this car.

Just stop.
I know, that's why I responded to the guy to read his owners manual and it will tell him vs him having to ask or "try it."

Get that through your head.
 

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Dyno tests from several aftermarket suppliers have shown that higher octane fuel does produce more hp (about 9 - 11 hp iirc) but for whatever reason, Honda has decided to omit that information from the owner's manual, stating omly that the fuel must be a minimum of 87 octane. See Post no. 8 in this thread for Hondata's results. KTuner posted a similar graph somewhere, but I'm too lazy to look it up. :)
 

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Discussion Starter #65
I'm assuming you're aiming this at me. I didn't say it doesn't make a difference. I said it doesn't make a difference if your vehicle can't take advantage of it. I also said such information would be present in your owners manual and that you wouldn't have to waste time/effort/money/brainwaves "trying it."
Why are you so hung up on what the owners manual states? Do you write the owners manuals for Honda? Are owners manuals always 100% inclusive of every piece of information?

The owners manual states: Fuel recommendation - Unleaded gasoline, pump octane number 87 or higher

It doesn't say anything about "use 91 for better performance" or "use of 87 is acceptable but you may notice a decrease in performance."

Think about it from a marketing perspective. Being able to use 87 octane in a turbo car is a huge plus for the vast majority of owners. They don't want to think the ECU is having to hold itself back because of this to keep knock under control. As long as it achieves the stated 252hp or more, everybody is happy. Honda has nothing to gain by stating this in the owners manual.
 

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My 1972 F100 will get absolutely zip from higher octane gas. Ditto my 1994 Suburban. Both rigs will burn it just fine but won't gain from it. If your Honda whatever has the ability to adjust the timing to get more power it will say so in the owners manual.
At the risk of beating a dead horse and to repeat what others have stated, the owner’s manual is NOT the proper source of information for this. The fact that the owner’s manual does specifically state that higher octane produces more power does not mean it is not true. By the way, you are very correct to say that only high compression engines benefit from high octane fuel. But turbo charged engines behave like EXTREMELY high compression engines.

If a naturally aspirated engine has a compression ratio of 10:1 and runs at sea level where the air pressure is 14.7 psi, that engine should have about 147 psi at TDC. That cylinder pressure implies a fair amount of heat. I recognize that there is a fiddle-factor involved, but if you turbocharged that same engine and ran 14.7 psi of boost, you would have doubled the amount of air entering the cylinder and in effect doubled the cylinder pressure. The compression ratio remains the same but you are compressing twice as much air. The cylinder pressure should be about 294 psi at TDC (Again, some fiddle-factor will be at play.) That would be like a naturally aspirated engine with a 20:1 compression ratio.

https://www.rbracing-rsr.com/compression.htm

Honda’s 2.0T runs more than 20 psi at full boost. With a 9.8:1 compression ratio that implies a cylinder pressure of about 340 psi. That resembles a 23:1 compression ratio in a naturally aspirated engine. (You're in diesel territory!) Given that cylinder pressure, I find it amazing that the computer can alter the ignition timing (and boost) enough that Honda’s 2.0T can operate on 87-octane with no knock. For that matter, I'm amazed the engines don't blow head gaskets or bend rods.

The bottom line is that all turbocharged cars today endlessly pull timing to avoid engine knock. Most are designed to operate on 96-octane fuel. On 96-octane, the computer will use its most advanced ignition map. If you run anything less than 96-octane fuel, the engine will knock and the computer will pull timing. If you run higher octane (up to 96), the computer can and will take advantage of it. Running premium fuel in Honda’s 2.0T will absolutely boost power.

EDIT: For completeness, when the spark ignites the fuel-air mixture and that flame kernel expands, cylinder pressure will spike and can easily triple to quadruple what the "base" pressure might be. That spike in pressure and heat is what requires proper octane for controlled combustion. If the octane is inadequate for that level of heat/pressure, a secondary "explosion" will begin near the perimeter of the cylinder as the primary charge expands. That secondary combustion, in conjunction with the primary combustion started by the spark plug, will create a further spike in cylinder pressure, so great that it can push the valves and pistons sideways and create the dreaded ping/knock. To prevent that, the computer retards timing to start the combustion process later in compression stroke and allow less flame kernel expansion before the piston passes about 18° ATDC (that's 1/10th of the way down during the power stroke.) This implies some of that heat expansion is wasted and reduces power.
 

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Will the accord with 1.5 running 93 octane improve on power as well? As the 2.0?
New here, just signed for a 2018 1.5 Sport Accord, and have done plenty of reading on boosted cars while recently looking to buy. Many brands out there are boosted now, I spent a lot of time looking at Ford ecoboost models and have found the same as reading about the Honda's. Fords 2.0 in the Edge says premium, but in other models it would say regular. According to owners, you can run 87 in an Edge, but it reduces power. As with here, people have posted their impressions and scientific data.

From my Ford and Honda owner reading, and from people that understand turbo, I think the simplest answer is that most of these newer turbo engines coming out can handle the range of fuels, but do have the ability to improve power via knock detection if you run 93 over 87. When one says 10hp increase, someone has to decide if their wallet wants that. Neither 87 or 93 are going to damage the engine (that I can tell), the engine seems to adjust to what you give it.

I do not concern myself with fuels costs, or even the 10 hp gain or whatever. I like to drive "spirited", and I intend on running 93 for more than one reason in the 1.5 turbo. I appreciate all the people that took time to post data, over just saying the manual says 87 or higher.
 

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I do not concern myself with fuels costs, or even the 10 hp gain or whatever. I like to drive "spirited", and I intend on running 93 for more than one reason in the 1.5 turbo. I appreciate all the people that took time to post data, over just saying the manual says 87 or higher.
It's your money so knock yourself out. I tried high octane in a few tanks and noticed zero difference in day to day driving. I'd rather keep my money and lose 10hp than make oil company executives richer but that's just my skepticism spidey sense tingling I suppose.
 

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It's your money so knock yourself out. I tried high octane in a few tanks and noticed zero difference in day to day driving. I'd rather keep my money and lose 10hp than make oil company executives richer but that's just my skepticism spidey sense tingling I suppose.
I like how you selectively did not quote this statement by me:

"When one says 10hp increase, someone has to decide if their wallet wants that. Neither 87 or 93 are going to damage the engine (that I can tell), the engine seems to adjust to what you give it."

Basically, do what makes you happy. The data is there, the only decision now is what you and your wallet decide, yet folks still have to come in and act like the data is false or call out others decisions with skepticism. Been on car forums for over 20 years now, and it has always been this way so I should not expect it to change. Present data and some still will not believe it no matter what you do.

This goes along with say an exhaust or CAI. I added a secondary device to my Scion xB (changed engine map) which required it to run 93, along with a TRD intake and Borla exhaust. By the dyno in town, those additions added 27hp at the wheels. Just driving it, I did not notice a lot except for in certain circumstances (like racing another xB). You get used to it, plus the butt dyno is by far the stupidest thing ever for rating a performance item.

All those additions ran me about $900. So once again, you can call me dumb for doing that for 27hp, but it was my money and I got the result I wanted. Don't tell me what to do withy my money, and I won't tell you what to do with your money, simple way for every poster to handle performance threads. Learn what you can from it, and either try it or move on.
 

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newer turbo engines coming can handle the range of fuels, but do have the ability to improve power via knock detection if you run 93 over 87.
Agreed. And it goes both ways. Running premium in the Accord will boost power over 87-octane. And while you must use premium in the Civic Type R to produce its 306 hp, Honda's website clearly states the Type R's required fuel is "regular unleaded." Apparently even that high performance turbo can run just fine on regular. Premium is "only" recommended. Today's turbo engines can handle a wide range of octane.
 

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It's your money so knock yourself out. I tried high octane in a few tanks and noticed zero difference in day to day driving. I'd rather keep my money and lose 10hp than make oil company executives richer but that's just my skepticism spidey sense tingling I suppose.
I wasn’t going to get back involved in this thread, but wanted to comment on your post. If you are driving conservatively, you likely won’t notice any performance gain from higher octane.. let alone most mods. The gains are found at WOT. Fill up with premium again and open it all the way up.

But I agree, if you aren’t worried about a few extra ponies and you don’t drive aggressively, then definitely stick with the 87.
 

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Thanks for response and assurance guys. I will deff be fueling up with 93 from now on. My 1.5 could use the extra kick.
 

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I live in Utah. Can I fuel my Civic 2.0 EX 2016( non turbo) with 85 and Accord EX-L 2018 with 87? I have been fueling my civic with 85 for 2 years and I have had no problem. Only my accord uses 87 because it has turbo
 

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I live in Utah. Can I fuel my Civic 2.0 EX 2016( non turbo) with 85 and Accord EX-L 2018 with 87? I have been fueling my civic with 85 for 2 years and I have had no problem. Only my accord uses 87 because it has turbo
I think you have it right.

Air pressure at sea level is 14.7 psi. At 6,000 feet above sea level, air pressure (same temperature) is about 11.8 psi. With 20% less air, there is about 20% less pressure in the cylinder during the compression stroke (naturally aspirated engine). Less pressure means less heat. Because less heat during the compression stroke naturally resists detonation, the engine can operate on lower octane fuel and still not knock. Therefore 85-octane in your Civic is perfectly fine.

However a turbocharger will still hold very close to full boost at higher elevation. It might take longer to spool, but it can eventually add another ≈20+ psi to the base 11.8 psi. While cylinder pressure and heat may not be quite as high as at lower elevation, it is close enough that the engine still requires 87-octane to control detonation. Turbos should still use 87-octane fuel (or whatever the manual states) at elevation even though it may be considered “mid octane” for naturally aspirated engines.

With regard to your Civic, if you intend to travel “down” from your area of Utah to an elevation in which regular fuel is once again 87-octane, the 85-octane fuel you still have in your tank from higher elevation may cause engine knock. It is recommended to fill with 87-octane fuel ASAP, or if you still have ½ a tank of 85-octane, to fill with 89-octane to raise the average octane in the tank to 87-octane.
 

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My response might suit for any fuel grade discussions:

Try a few tanks of 87 vs 93 to see if there is a difference, no need for theories/analysis or opinions.

At least, 93 is not worse than 87, and will not harm your engine: notice the gas cap markings "87 and above".

I tried premium on my 3rd gen. Yes, there is a difference, which led me to use premium on long trips.
I tried premium on my 7th gen. Somehow I didn't notice any difference so far, but I haven't been driving it for long distant trips.
 

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My response might suit for any fuel grade discussions:

Try a few tanks of 87 vs 93 to see if there is a difference, no need for theories/analysis or opinions.

At least, 93 is not worse than 87, and will not harm your engine: notice the gas cap markings "87 and above".

I tried premium on my 3rd gen. Yes, there is a difference, which led me to use premium on long trips.
I tried premium on my 7th gen. Somehow I didn't notice any difference so far, but I haven't been driving it for long distant trips.
Respectable data has already been posted here, that if you run 93 the computer does not pull the timing near as much. As stated before by me, run 87, run 93, doesn't matter. If you want the most juice from the car, run 93.

There is no arguing this, it has already been proven.
 

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@tisuanhoc87 asked about fuel as it relates to high elevation. Regular fuel is 85-octane up there. 87-octane is mid-grade fuel up there, like 89-octane is mid-grade at lower elevation. Knowing that he can safely run "regular" 85-octane in his NA Civic, he wanted to confirm that he still needed 87-octane in the new Accord due to the turbo, even though it is considered mid-grade octane at high elevation.

(EDIT) I think his question was more about avoiding potential engine damage than using higher octane to boost power. Even though the turbo Accord is designed to operate on regular fuel, which is 87-octane for most of us, running "regular" 85-octane at high elevation would probably cause too much engine knock for the ECU to compensate. Because the turbo compensates for thinner air, the turbo still needs 87-octane, even up there.
 
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