Effect of 93 octane

[MossRoad]

You F-150 drivers will want to read this: Is Premium Gas Worth It? We Test High Octane on 4 Popular Vehicles

It's the only vehicle where 93 octane was a big improvement over 87 octane. On the BMW, the 87 octane was better.

On my own tests in the MX-5, I've settled on 89 (probably more nearly 90) octane for it. Think the owners manual recommends 91.

Ralph

Initially, one would think that means the higher octane fuel has more power, but it doesn't.

In reality, it just detonates later, allowing the computer to alter the timing, which produces more power.

 

[snymat68]

Our 2013 Impala has 11.5:1 compression and runs on 87 octane.

It's all about the computers now.

As does my 2013 Camaro with the same compression ratio. BUT it runs BETTER on 93. Why? Because, just like you said, computers.
ECU's have lookup tables and will ****** the timing automatically to prevent predetonation if the knock sensors detect it.
Yes, my car will run just fine on the 87 (the manual even says so), but the 93 lets the engine perform to its full potential.

 

[MossRoad]

As does my 2013 Camaro with the same compression ratio. BUT it runs BETTER on 93. Why? Because, just like you said, computers.
ECU's have lookup tables and will ****** the timing automatically to prevent predetonation if the knock sensors detect it.
Yes, my car will run just fine on the 87 (the manual even says so), but the 93 lets the engine perform to its full potential.

Yes, I believe we have the same engine. Good luck with that. I drive it pretty hard. The cam shaft phasers malfunctioned and snapped the camshafts around 100,000, which ate the engine. Replaced with a junkyard engine with 58,000. I really like the way that engine revs. More like a motorcycle than cars of the past. But I do not think it's as durable as the 3800 series II that we had in the 2000 Impala. Too many moving parts, sensors, etc.... It does get very good MPG. Quite impressive to get 31MPG in a 4 door sedan cruising down the road at 75MPH with the RPMS around 1700.

 

[dodge man]

I own a 2010 Challenger I have a tuner for it with which I bumped up the timing and leaned out the fuel based on a dyno tune. With that you can record data to a laptop and view it latter. You can choose what you can record to the laptop, and you realize what all the different things the computer in a car looks at. Two of them that were critical were called short term knock ****** and long term knock ******. The short term is not a big deal, the engine is just pulling timing briefly based on feed back from the knock sensors. The long term knock ****** is bad. Say you are running 85 octane and really need 93. If you keep getting timing pulled at certain rpms and conditions, the computer will store that info and that timing will be pulled from then on until a computer reset. I don't know if all car and trucks have a similar system or not, but running to low of an octane all the time could have negative performance issues. Around here 87 octane is as low as it goes but I know in Colorado, 85 is available.

 

[snymat68]

Yes, I believe we have the same engine. Good luck with that. I drive it pretty hard. The cam shaft phasers malfunctioned and snapped the camshafts around 100,000, which ate the engine. Replaced with a junkyard engine with 58,000. I really like the way that engine revs. More like a motorcycle than cars of the past. But I do not think it's as durable as the 3800 series II that we had in the 2000 Impala. Too many moving parts, sensors, etc.... It does get very good MPG. Quite impressive to get 31MPG in a 4 door sedan cruising down the road at 75MPH with the RPMS around 1700.

I'm somewhere around 102k on mine. I've used it for drag racing, autocross, and don't baby it as my daily driver year round. (Knock on wood) So far so good. Hopefully it holds out because I plan to have it at least another 5 years!

 

[oosik]

It's very simple. The 6.4 liter engine in my Taco Wagon will produce 410hp with the recommended 89 octane fuel. That's what I use. I've got 9800 miles on the truck and get 18+ mpg. I'm very happy.

 

[KennyG]

Woonder why we are diffferent, only see 91, 98 and E10.

I think the rest of the world uses a different method of reporting octane rating. There is research octane and motor octane. The US uses an average of the two and most everyone else uses research octane. No surprise there.

 

[MossRoad]

I'm somewhere around 102k on mine. I've used it for drag racing, autocross, and don't baby it as my daily driver year round. (Knock on wood) So far so good. Hopefully it holds out because I plan to have it at least another 5 years!

Stick or auto? We have auto. I dislike the way it interacts with the slow timing of the throttle-by-wire. I step on the gas pedal, nothing happens, so my brain says "step harder', but in that instant of brain-to-foot time, the throttle catches up with my initial step, and it ends up pushing it too far, the car accelerates faster than you want, and it jerks your neck. I know there's some tunes out there that can clean that up. Just deciding if I want to go that route.

 

[wheelbuilder]

I've tracked the mileage and has octane on my current car (an 09 Subaru Legacy) over 10 years. I've used 87, 89, and 91 octane (the 91 is ethanol free). My data from that shows the car gets about 3 mpg better mileage do the the 91 than the 87 and the 89 is about 1 mpg better than the 87.
Lately, I've been buying the ethanol free 91 octane for the mileage. Its about a wash cost wise between the different octane and the extra distance I can drive.

The service manual says this engine has 10.7:1 compression. It must ****** the timing pretty hard to get away with 87. I don't think an old v8 could run well with that compression and octane.

 

[RalphVa]

From my understanding, higher octane is the resistance to explode. Low compression engines require lower octane, high compression engines require higher octane to prevent detonation before the spark plug ignites when the piston hits top dead center. My supercharged jaguar, being supercharged, requires 93 octane because it's a high compression engine. My hummer h2, which is a regular old gm 6 liter v8, is fine with 87 because it's a low compression engine.

Not true about low/high compression engines. The Mazda 3's engines (2.0 and 2.5) are about 13/1 compression ratio and run 87 octane. These are the "Skyactive" engines. Mazda is expected to soon come out with an even higher compression ratio gasoline engine that uses no spark plugs. They're in testing. Think the bugaboo with higher compression, like the 17 to 20ish for diesels, is the generation of more NOX in the exhaust. This starts being a problem somewhere past 13/1.

The Mx5's 2.0 engine, on the other hand, is tuned for 91 octane because of its valve/ignition timing, but it'll run on anything from 87 to 93 octane.

Ralph