87 or 91 Non-Ethanol?

[AugustneverEnds]

I have always filled my car with 91 non-ethanol for it's entire life with me (5 plus years) Recently my local station began carrying 87 non-ethanol so I decided to try it since I'm running stock. Since that fill-up I have experienced hesitation under full throttle acceleration and the occasional stumble. Last year I had similar problems when it was damp out thanks to a cracked rotor cap, crappy spark plug wires, and a tired ignition coil all of which I replaced and had smooth sailing for the rest of summer and fall. It has been rainy here lately but I really can't believe it's any of those parts at fault again.

I have nearly burned up all of the 87 and just refilled this morning with 91. I'm curious to see if the fuel is the cause and if anyone else has experienced anything so dramatic from a change in fuel.

[Ron]

FWIW, the fuel rate in the manual does not use the same rating as here in the US...Our Regular is OK to use in a stock engine.

Higher octane is harder to ignite, etc., so if you didn't re-tune your engine, it's not going to run the same. A lot would depend on if you pushed the limits allowed when setting it up originally (timing, CO...).

[Michael]

I just wanted to get in at the begining of what will be a very long and drawn out thread.

FWIW I have a stage II and always used 93. Sometimes non ethanol sometimes not. Almost 10 years doing this.

Also the number at the pump is not exactly a octane level as much as it is a anti knock rating. Lots of info in googleland about this and ypu can read all about it or just wait for Vegas or David T to write a book about it below.

[eight8toy]

In the words of Ace Ventura, "It's a high performance machine, so I had to fill it with premium."

Mine is stock engine, dont drive it often so she gets 91 only.

[nullset]

In the words of Ace Ventura, "It's a high performance machine, so I had to fill it with premium."

Mine is stock engine, dont drive it often so she gets 91 only.

Higher octane fuel is not better. It is literally only intended for engines that require it to prevent knocking.

If you put 91 octane in an engine designed for 87 octane, it will not in any way improve things.

If you put 87 octane in an engine designed for 91, you might experience "knocking" (aka precombusion). Modern engines detect this and drop into a lower performance mode.

tl;dr: Don't waste your money on "premium" gas for stock engines.

[DMC-81]

In the Delorean, I use 87 non-ethanol without problems. I recently discovered a station that sells 89 non-ethanol. After filling up on that, I notice very slightly more power. (I don't know why that is. Maybe it's just my perception.)

In my daily Driver (Magnum R/T) I normally use 87 regular (contains ethanol). From time to time, I treat it to 91 or 93 whatever Shell's best is. I immediately notice extra power. I asked my brother who works in the crude refining industry why that is, and he said that as the octane rating goes up, there is typically less percentage of ethanol, and that ethanol provides less punch than gasoline. He said that 91 or 93 typically contains very little ethanol. I guess it make sense as the pump labels state that "all gasolines contain up to X percent of ethanol"). They don't state what that X % is in any one grade.


I wonder if the OP got a bad batch of 87 non-ethanol? I would wait to see if the new fill-up of 91 makes the problem go away.

[AugustneverEnds]

I just wanted to get in at the begining of what will be a very long and drawn out thread.

FWIW I have a stage II and always used 93. Sometimes non ethanol sometimes not. Almost 10 years doing this.

Also the number at the pump is not exactly a octane level as much as it is a anti knock rating. Lots of info in googleland about this and ypu can read all about it or just wait for Vegas or David T to write a book about it below.

Haha With this thread I am expecting some novel length responses and some vehement disagreements.

[Nicholas R]

If your engine is still the stock 8.8:1 compression, an octane boost isn't going to change anything. The only thing more octane does is reduces a fuel's tendency to pre-detonate due to cylinder pressure (rather than due to the spark ignition). It's why high compression race cars need 100+ octane, and low compression commuter cars are fine on 87.

[Jonathan]

I use 87 octane in my stock engine. And I don't seek out stations that carry non-ethanol because, among other reasons, they are so few and far between that I can't be bothered with the hassle. I generally stick with the main stream stations around here like Esso, Petro-Canada and Pioneer.

I looked back at my logsheet of fill-ups and it seems I used to put 91 octane in the car from when I got it in late 2007 until the end of the 2010 season. That was 432 litres over 21 fill-ups and approximately 1,960 miles travelled (bad speedo). Equates to only about 17 MPG, but granted the car was not running well or at all for much of that so take it with a grain of salt.

Since the start of 2011, I have put in 1,888 litres of 87 octane across 84 fill-ups and travelled 11,651 miles (with a mostly functional speedo so reasonably accurate). That's about 23 MPG, in a car with most things working properly. Stock engine, stock exhaust, auto trans.

Personally, I think 87 octane is what is best for the car and I don't fuss much with seeking out non-ethanol fuels. Not because of the ethanol laced fuels being better or worse or in between, but only because it's not terribly practical trying to use only that. That's how I feel about it... YOUR MILEAGE MAY VARY... HAHAHAHAHAHA!!!

[dn010]

FWIW my D when stock historically ran different (worse) in the rain and despite throwing a ton of parts at it I never got that one solved. I used to give it 91 at first but when harder times hit I only fed it 87, which I still do to this day even with the B280F engine. Never saw a difference even when I tried octane boost additives.

The bad batch comment above is in my opinion rare but does happen. I filled up my daily once and noticed my fuel gauge had not moved at all. Later that evening I went checked it and it had moved up slightly - driving it over the course of days it slowly crept up and settled to where the tank level was. Once the tank got low my engine misfired and ran like crap to the point I barely made it home. Hours later I restarted the car and it ran fine like nothing happened, and I've never had that happen again in the same vehicle to this day and that was maybe 4+ years ago. Bad batch is all I could think it was.