Higher Octane...bad?
 

With my on going crusade over at Dodge Forum someone just posted this.

Is there any validity to this? I've always thought engines just advanced timing to meet whatever octane there was... (new engines, I know old engines don't)

AFAIK, modern ECUs retard timing to prevent engine damage with lower octane fuel. I don't know why they should advance timing in anticipation of higher octane fuel. I'd have stated it differently:

...yes, the "new" engine-management computers actually *WILL* advance the timing to "take advantage" of higher octane (less knock-prone) gasoline.

...that's *part* of the reason why some of the "newer" cars can often achieve better FE when using E85-fuel, which has 105 octane rating, due to ethanol's much higher octane rating (113) than 'straight' gasoline.

http://www1.eere.energy.gov/biomass/..._car_graph.jpg

...so, the real answer may lie in what year vehicle the guy was talking about--pre-electronics carburation, OBDI or todays' OBDII?

It doesn't make sense to spend more money on higher octame fuel if your engine is not knocking, and definitely not if the manufacturer calls for lower octane.

"Higher octane" does not mean "higher quality", as some people seem to think.

Here in Colorado there is ethanol in all grades of fuel. Don't know for sure, but I'm guessing that they just put more ethanol in the higher octane fuels and charge a lot more for the effort, while they put mostly ethanol in E-85 and charge a lot less for it. Go figure.

If I had engine knock I would buy mostly low octane and mix in a little E-85 to find the right mix and save some money, but at this altitude the burn is slowed naturally by much thinner air, so there isn't much need for higher octane fuels. Sure doesn't stop people from buying it though.

We're talking about OBDII.

This is pretty much the conversation we have been having about it. (the last 2-3 posts)

Does everybody get it?

Um, generally fully functional OBDII cars cannot knock (at least not detectably to the driver)

If you have a timing guage and tap on an OBDII motor with a ballpean hammer lightly the timing retards rapidly.

So higher octane "May" improve some factor of performance, my Buick for example running hi test in the winter has its FE restored to summertime levels but the effect doesn't pass into the summer sadly. Also the additional cost exceeds the gain most of the time.

But I can't say hi octane is not beneficial in some circumstances, Ever try to run an older Smartcar on 87 octane ethanol? It is well rather craptaskic.

Also my Dodge gets BETTER FE running 100+ octane e85 mixed 50/50 with 89 octane e10 in the winter (again effect does not seem to translate into warmer weather)

Cheers
Ryan

I am not advocating using higher octane. I am asking: Does using higher then approved octane (Premium) shorten the life of an OBDII engine meant to run on 87 (Regular)?

...two letter answer: no.

...octane is a "knock-limiting" value and basically nothing else! So, using 91 octane ("Premium") in a car designed for 87 octane ("regular") will NOT damage it whatsoever.

...what can damage an engine, however, is using different fuels containing god-knows-what-kind of additives that don't burn cleanly.

...this has NOTHING to due with octane--but is, too often, one (of many) false claims made for the additives--but rather the "left-over deposits" from faulty combustion, which CAN by themselves cause "glowing carbon" deposits which CAN result in pre-ignition and cause damage (if the computer can't yank the timing back quick enough).

...read the WIKI explanation for octane, it should help you come to your own answer.

Is it E10 89 or 100% gas 89?

87/89 octane is all e10 around here, a couple stations carry 100% gas on their 93 octane.

I buy both grades out of the same pump at Renew energies stations that sell e10/20/85.

Cheers
Ryan

An engine can still knock with a knock sensor but the knock sensor prevents it from knocking more than that until conditions change. With a knock sensor the octane doesn't affect engine life as much as it affects power. Current Generation Premium fuel engines will run on less than Premium but their power output is less. Without a knock sensor running too low of an octane fuel will kill an engine before a high octane motor.

The only thing I can believe he is referring to is a little understood event when a high octane fuel(like alcohol) is used in a low compression engine and the timing is retarded past a certain point. The idea is that the fuel may ignite into the exhaust stroke before it completes combustion and damage may occur. In this case I'm speculating but some of this may have to do with lean fuel-air mixtures which reduce flame speed. Engines that try to run alcohol may retard under, I forget what it's called when this happens, but it actually makes it worse. I actually believe that an alcohol motor needs to have more timing advance when it's run lean.

And with that I doubt he has any idea of what he is talking about. Recommended octane is a minimum value. Going a few octane higher will not lead to shorter engine life. Running unleaded Race gasoline in a motor isn't going to kill the motor from high octane. Unleaded Race Fuel only goes to 99-103 octane anyway.

I have advanced the timing on my cars engine to get a little more oomph and to get rid of the stuttering and knocking it gets with low octane fuel (93 RON is the lowest available here)

Good thing 95, 97 and 100 RON gasoline is readily available at gas pumps throughout the city.

What nonsense did I write!? :eek:

Anyway, :snail: advancing the timing will raise the octane requirements. What you're doing is raising the dynamic compression ratio and it will probably knock worse on the 93 RON crap, that's about 87 AKI octane if I remember correctly.

Just a bit of an addition, I've found some newer cars that require regular will run better on Premium. :thumbup: For example the new 3rd Gen Ford Focus only requires regular 87 AKI octane but it says in the manual that it will run smoother and better on premium. Which also means it should run a bit better on E85 since the 2012.5+ MY is FFV. But the only guy I know running E85 in a '12 Focus is getting about the same efficiency as Gasohol. Average for the new Focus seems to be around 32 MPG on Fuelly so it's not terrible but he's done 42 or so with Gasoline.

The Honda Fit might be one of those too but I need to verify first.