Octane Question

[tr7driver]

While driving across the country a couple of weeks ago, I noticed that "regular" grade gasoline here in Illinois is 87. In Western Nebraska it drops to 86 and in Wyoming and Utah it was 85. I understand that fuel blends differ regionally for emissions factors. I was wondering what impact the change in octane had on emissions. I think some of the difference would be related to elevation, but its not unusual for elevation to change several thousand feet over a few miles in the Rocky Mountains.

 

If the recommendation is to run on "regular" gas do you just go with what's available called regular, or should you buy the "higher grade" 87 octane gasoline in these areas? I stuck with the regular grade, what ever the octane was, and had no issues traveling through the western mountain elevations.

 

Page 145 of my owners manual addresses the octane ratings of the 2.5L, the 1.6L and 2.0 ecoboost saying to use 87, but has not information for the hybrid engine.

Edited July 1, 2014 by tr7driver

[murphy]

Page 145 of my owners manual addresses the octane ratings of the 2.5L, the 1.6L and 2.0 ecoboost saying to use 87, but has not information for the hybrid engine.

You are looking at the Owner's Manual for the standard gas only Fusion.

 

The Hybrid/Energi version of the manual does not call out those engines.

 

It says not to go below 87 octane.

[lolder]

You're not going to hurt it using the 85-86 mountain grades.

[GrySql]

Strangely my Ford Flex Owners Manual suggests using 91 octane when mountain driving, carrying heavy loads and towing.

The FFH's Atkinson engine is different and 87 octane has worked fine from 11,500' to sea level for my FFH.

[lolder]

Is your Flex turbo-charged? Higher octane lets you get more HP with more fuel and air that a turbo charger can give you. More HP per cubic inch displacement.

[GrySql]

Mine is the 3.5L naturally aspirated..

The OM has a lot more info on octane for the turbo engines.

 

FTA:

3.5L V6 engine

Your vehicle will run normally on 87 octane regular fuel. Premium fuel will provide improved performance.

 

I'm off-topic, just thought it was interesting to see in an OM.

[machoman1337]

I didn't know that there were octanes below 87! I guess I need to visit more states.

[Ryan Goodlett]

You're not going to hurt it using the 85-86 mountain grades.

 

I don't know if you are right or wrong, but my hunch is that the 87 is there for a reason. Think of octane as the resistance to pre-ignite the fuel (no spark needed like a diesel) You want the spark plug to ignite the fuel at the precise timing the engine requires (control the combustion). With 93 the timing will be reduced and with 85 the timing advanced. With advanced timing you run lean and 85 rich. You end up with spark knock and the like running 85. In the end I see 87 as the preverbal sweet spot for our engine.

[lolder]

All cars now have knock detection that won't allow it to happen. You can run cars that call for premium on regular with only a top end HP loss because of that.

[Ryan Goodlett]

All cars now have knock detection that won't allow it to happen. You can run cars that call for premium on regular with only a top end HP loss because of that.

Preignition is different than knocking.

[kuzzi]

Atkinson engine has less compression than the otto engines. In our engines, the volume ratio of the whole cylinder to the combustion chamber (compression ratio) is 12.5:1 which in most engines would require high octane 90+ fuel. The late intake valve closing reduces this to some unknown number but I'm willing to bet it's around 10:1 with a slightly advanced timing, which allows use of lower octanes. Ford is protecting itself and your car by suggesting 87 octane minimum. You may be relying on the knock detection system to handle 85 octane, but it should still run fine.

[Easy Rider]

Preignition is different than knocking.

Really ?

 

Pre-ignition when not severe is often described as a "ping".

When it gets worse, it is a knock.

 

What do you think the difference is ??

Of course other things can cause a knocking sound too.

[acdii]

You're not going to hurt it using the 85-86 mountain grades.

Those states that have 85 as regular grade are at higher altitudes, so their fuel grades are lower to compensate for the thinner air. Their premium is usually the 89 octane. I experienced this myself when I drove to Chino CA a few years ago in my F150 EB. I was only able to get 85 a couple times, but had no performance issues using it.

[Ryan Goodlett]

Really ?

 

Pre-ignition when not severe is often described as a "ping".

When it gets worse, it is a knock.

 

What do you think the difference is ??

Of course other things can cause a knocking sound too.

 

Not normally my source of information, but the difference is fairly well written and described at the beginning of this Wiki page.

 

http://en.wikipedia.org/wiki/Engine_knocking

[lolder]

I had a '59 Volvo way back that required high test. I got really low on gas and put some 80 octane AV gas in it at the little airport I was hanging around. It ran fine but it wouldn't shut off. It idled completely normal indefinitely after I turned the key off. I had to pop the clutch in gear to stop it. Now that's pre-ignition.

[GrySql]

I had a '59 Volvo way back that required high test. I got really low on gas and put some 80 octane AV gas in it at the little airport I was hanging around. It ran fine but it wouldn't shut off. It idled completely normal indefinitely after I turned the key off. I had to pop the clutch in gear to stop it. Now that's pre-ignition.

:) Love it...

A Volvo PV544?

[lolder]

Yes.

[Easy Rider]

 

Not normally my source of information, but the difference is fairly well written and described at the beginning of this Wiki page.

 

http://en.wikipedia.org/wiki/Engine_knocking

That article makes an artificial distinction between two terms which, in common usage, do NOT impart the meanings given there.

 

IF.....ANY of the fuel mixture ignites before it is supposed to, that IS "pre-ignition".

Makes no difference if it occurs before the spark or after.

If it happens early, it is by definition "pre".

 

Or to put it another way, pre-ignition does NOT use the spark as a point of reference because that precise timing moves depending on several conditions.

 

Pre-ignition means that the mixture ignites before it is supposed to.

The normal result of that is a ping or knock.

There are other things that can make a knocking sound too.

 

Saying that pre-ignition and knocking are two different things is just unnecessarily confusing the issue.

 

Pre-ignition almost always results in some kind of pinging or knocking noise.

Conversely, a knock is not always caused by a fuel ignition problem.