90 octane: The new premium ???

Messages
5,763
Location
Da Swamp
At a pass by several of my local gas stations this morning, I saw the newest dodge by which the oil companies will give us less for more money: 90 octane is the number on the premium pump instead of 91 or (as it's been for a number of years here) 93. Same ~14-15% surcharge over regular as when it was 93, of course. Is this the latest version of "keep the package the same price but put less in it" that we see at grocery stores? Or is it just in my benighted area? I planned to run a couple of tanks of 93 through the Regal -- am doing so now, and have seen about 15% mpg increase according to my Driver's Info Center. There's still one or two local stations with 93, but how long will that last? And what are people with cars that specify 91 as a minimum to do now? Grrrr.
 
Messages
2,392
Location
SD
Haven't seen that here yet. I suspect you're right about the "keep the package the same price but put less in it" theory.
 
Messages
32
Location
Vancouver Canada
Does your Regal owners manual say to use higher octane fuel? I've heard it quoted before, and I still don't understand how using higher octane gas gives better gas mileage.
 
Messages
2,392
Location
SD
Originally Posted By: speedyb
I still don't understand how using higher octane gas gives better gas mileage.
It doesn't apply to all vehicles, but some will advance the timing until they detect knock (pinging). The higher octane gas will allow it to advance the timing further.
 

Benzadmiral

Thread starter
Messages
5,763
Location
Da Swamp
Originally Posted By: speedyb
Does your Regal owners manual say to use higher octane fuel? I've heard it quoted before, and I still don't understand how using higher octane gas gives better gas mileage.
It doesn't say that specifically; "87 or higher" is the recommendation. However, my 4-cylinder engine has fairly high compression, 11.4:1 or something like that, and several posters here suggested it might be worth my while to run a couple tanks of premium and see if the engine could take advantage of the higher octane. It seems to: the DIC's mpg readout, which since I've owned the car has always been pretty close to what I get with the manual calculation method, is reading 26.5 over the last week. On 87, which I've used since I bought the Regal, it usually read 23 and a fraction. And I'm driving the same routes in the same way, under the same temps, with the same use of A/C and the same tire pressure, as before. Of course it's not lab testing, and it's way too soon to tell anything -- but it's kind of fun to examine it.
 
Messages
14,731
Location
Central NY
Originally Posted By: zrxkawboy
Originally Posted By: speedyb
I still don't understand how using higher octane gas gives better gas mileage.
It doesn't apply to all vehicles, but some will advance the timing until they detect knock (pinging). The higher octane gas will allow it to advance the timing further.
Yup. This. Any higher compression, DI engine will benefit from higher octane gas (Ford Focus, Ecoboost, Mazda Skyactiv, etc). Some port injected engines can. The 2.0L Duratec in my focus benefits and sees a mileage increase. The 4.0L AMC engine in my Cherokee ... no.
 
Messages
3,043
Originally Posted By: zrxkawboy
Haven't seen that here yet. I suspect you're right about the "keep the package the same price but put less in it" theory.
Like the propane tanks formerly know as 20lbers?
 

JHZR2

Staff member
Messages
46,128
Location
New Jersey
All the premium here is 93, but one chain started peddling 92 octane to lower the price. Thing is, all the cars I've seen specified for premium only want 91. I'm sure there are exceptions, but I suspect that tunings are done that way for a reason. And if vehicles only advance to 91 octane, it's silly to sell higher octane, as it may not radicalize and fulfill the combustion entirely (probably splitting hairs though). I've seen premi um lower than 91 but usually at high altitudes.
 

JHZR2

Staff member
Messages
46,128
Location
New Jersey
Originally Posted By: BISCUT
Originally Posted By: zrxkawboy
Haven't seen that here yet. I suspect you're right about the "keep the package the same price but put less in it" theory.
Like the propane tanks formerly know as 20lbers?
I buy by quantity, not an exchange, so I get and use exactly what I pay for for propane. Unless the thermal energy of 87 vs 93/91/90 differs substantially, it's not the same.
 
Messages
32
Location
Vancouver Canada
Originally Posted By: zrxkawboy
Originally Posted By: speedyb
I still don't understand how using higher octane gas gives better gas mileage.
It doesn't apply to all vehicles, but some will advance the timing until they detect knock (pinging). The higher octane gas will allow it to advance the timing further.
Ahhh, I understand now. Thanks.
 

gathermewool

Site Donor
Messages
8,927
Location
New England
I've also noticed an increase in gas mileage using slightly higher than spec'd 87, why anyone would run 93 in a car that spec's 87+? I run only the next highest grade, if I thought the ECU was pulling timing. That's not to say that using as high as possible as a gross indicator is a bad idea, but sustained use of too high octane has no benefit. To be clear, a vehicles brain bucket, the ECU or ECM, can only add so much timing, and that value is dynamically reduced based on knock sensor input. If no knock is sensed, the ECU will lookup the max timing that can be applied for the current conditions and that's what the timing will be - it will not add more if you change from, say, 89 octane to 91 octane if no knock was sensed using 89 octane. The same is true with 87 octane: if no knock is noted and timing is not being pulled, then adding any additionally knock resistant fuel will provide absolutely zero benefit.
 
Messages
14,731
Location
Central NY
Originally Posted By: nitehawk55
More important is it ethanol free gas ? That in itself will make a difference in performance and mileage
I have been running that in my vehicles. The cherokee cracked 20MPG (which isn't bad) using ethanol free gas and the Focus is getting 36MPG back and fourth to work - previously was 34. I'm not sure if it's the ethanol free gas or whta, but it's working
 
Messages
3,043
Originally Posted By: JHZR2
Originally Posted By: BISCUT
Originally Posted By: zrxkawboy
Haven't seen that here yet. I suspect you're right about the "keep the package the same price but put less in it" theory.
Like the propane tanks formerly know as 20lbers?
I buy by quantity, not an exchange, so I get and use exactly what I pay for for propane. Unless the thermal energy of 87 vs 93/91/90 differs substantially, it's not the same.
Scary how few places around me (Dutchess County NY) there are to fill a tank. Almost all are EX. Sickening. And the available hours of LP fill stations are, rightly so, geared toward the working man not the homeowner.
 

Benzadmiral

Thread starter
Messages
5,763
Location
Da Swamp
Originally Posted By: nitehawk55
More important is it ethanol free gas ? That in itself will make a difference in performance and mileage
Both the regular I've been using for the last month, and the premium I have in there now, are from the same station, and both are labeled ethanol free. Whenever I've used E10 regular, my mileage has been lower than with E0. I recall that in the mid-'90s, before I moved to Denver, the stations in Da Swamp all had 91 as their top octane. When I came back in '01, everyone had 93 -- and I needed it for my W126 Mercedes (and its successor, the C-Class). Though the big Merc ran beautifully on the mid-grade up at 5000+ feet. We'll see how this experiment goes; perhaps one more tank of 93, then I'll try some 89. Which, here, is only some .20 more than 87. So I'd only need to see a >7% increase in my overall mpg for its use to be worth while. . . .
 
Messages
11
Location
Pa
The higher the octane rating the more resistance it has to explode too early. Meaning if it fires too soon it may fire before the piston reaches it's compression stroke, which will result in an incomplete power stroke. Thus less power, more fuel.
 
Messages
43,667
Location
'Stralia
Originally Posted By: JHZR2
And if vehicles only advance to 91 octane, it's silly to sell higher octane, as it may not radicalize and fulfill the combustion entirely (probably splitting hairs though).
Octane is resistance to combustion due to temperature/pressure, i.e. autoignition. Once there is a flame front, it all goes, regardless of octane.
 
Top