Economy and octane

[johnl]

Since I bought the car (TS 147) a few months ago I've been running it on 95 octane fuel (as per the AR recommendation). The fuel is a BP product, not due to any preference, just that the BP is convenient for me. Driven in very careful granny fashion, the car would return about 7.6 to 8 L per 100km, driven 'normally' it was more like 8.5 / 8.6. (this is indicated economy on the trip computer, actual economy measured 'manually from brim fill to brim per km actually travelled is about 7% worse)

The last two tankfuls I've experimentally used the BP 98 octane. On first fill with 98, the engine initially seemed quit unhappy. I'm sure it was misfiring, or some issue that felt like misfiring (ignition timing changes?). At any rate, the car was 'surging' on light throttle, speeding up slightly then slowing slightly, then speeding up etc. This occurred for maybe 2 or 3 km as the engine warmed, something it had never done using 95. Then it stopped doing it, and hasn't done it since.

Now, on 98, the economy has changed (comparison over identical drives, my usual twisty hilly rural road commute). Driven very granny style I can do 7.1 l per 100 km. Driven 'normally' it will easily do 7.3 to 7.5. Doing the sums (with an 8c difference between 95 and 98 octane), it's easily more economical to use the 98 octane. Break even would be around 8L per 100 km on 98. The engine also feels (quite subjectively) to be just a little bit more powerful on the 98.

Interesting, considering that AR recommends 95, and an octane higher than the engine actually requires should make no difference. Maybe the 95 isn't quite actually 95...?

Regards,
John.

[kaleuclint]

My Mercedes is meant to use U95 as default fuel, and I've always run it on U98.  Haven't done the figures for an absolute cost-effectiveness assessment; I just know that it achieves better mileage with the higher octane fuel and I figure it's better stuff (might just be falling for the marketing hype about engine cleaning qualities there). 

Still annoying to see 117c per litre (with discount) on the servo board, and ending paying 149c...

I've noticed on various forums that Ultimate 98 seems to be preferable to V-Power for use in Alfa 159 1750s.  My cars get a long warming up every morning and I had noticed the exhaust fumes a lot more since I started using V-Power for the Flybuys points, enough for me to forgo the points and go back to Ultimate.

[bazzbazz]

I've noticed on various forums that Ultimate 98 seems to be preferable to V-Power for use in Alfa 159 1750s.  My cars get a long warming up every morning and I had noticed the exhaust fumes a lot more since I started using V-Power for the Flybuys points, enough for me to forgo the points and go back to Ultimate.

Exhaust fumes or water vapour/steam due to colder weather?

Baz

[johnl]

I just filled our other car (Saab 9-5) with 98, rather than the Saab recommended 95. I tried this some time ago and it seemed to make no difference to either economy or performance, but I just recalled that this was during a time when the cars economy was hopelessly appalling anyway (which turned out to be a bad O2 sensor that took me far too long to diagnose). With a good sensor now fitted it might make a difference. We'll see.

Regards,
John.

[poohbah]

For what its worth, I only use 98 octane in my V6 156, and generally get around 10L/100km using it daily in peak hour. If I do less peak hour running, and mainly do off-peak freeway or country runs, I can get below 9L/100km. My 156 is about 30% better than my 81 2.0L GTV with big twin Webers, which drinks like a Russian sailor on shore leave.

[kaleuclint]

I did consider that Baz -- coincided with the coldest weather.  Definitely more 'fumey'; I know this as I apply a minimum 10 minute warm up in such weather and it drifts into my workshop  .  Of course denser air might contain more suspended fumes...

John, Saabs are completely different case in point.  I will never put ethanol in my current cars and bikes, but as an ex-Saab owner I know that not only do the Ecopower engines like ethanol, they outperform using it.  For all that I reckon mine ran nothing but U98 for most of my ownership.  I think the placard under the bonnet said to use U91!

[johnl]

My 156 is about 30% better than my 81 2.0L GTV with big twin Webers, which drinks like a Russian sailor on shore leave.

But they do sound wonderful. Have to say that I was quite disappointed that my TS wasn't remotely as aurally exiting as my old 1.8 Alfetta sedan was (RIP).

I wonder whatever happened to the Alfetta, or at least the bits from it, as I disposed of it to someone who wanted to use the parts to make an Alfetta based Hot Rod (a T-bucket with Alfa engine and running gear, or something like that...).

Regards,
John.

[johnl]

John, Saabs are completely different case in point.  I will never put ethanol in my current cars and bikes, but as an ex-Saab owner I know that not only do the Ecopower engines like ethanol, they outperform using it.  For all that I reckon mine ran nothing but U98 for most of my ownership.  I think the placard under the bonnet said to use U91!

Mine (well, my wife's car) is the 'low boost' version, not the much more potent 'Aero' version. It's a very pleasant / relaxing / effortless car to tour about in, but not at all sporty. The Saab recommendation is 95 octane, though they do say 91 is OK if necessary (with "reduced performance and economy"). Haven't tried any ethanol polluted fuel, religiously opposed to it...

Regards,
John.

[poohbah]

They sure do sound wonderful John - I love the way my GTV barks (the sports exhaust certainly amplifies things). I now own two of what I reckon are among the best sounding cars ever built.

[johnl]

They sure do sound wonderful John - I love the way my GTV barks (the sports exhaust certainly amplifies things). I now own two of what I reckon are among the best sounding cars ever built.

The V6 engines do sound very nice, pity the 4 cylinder is so disappointingly bland in this respect (why, when the older ones did sound so nice??). I wish I could make it sound more like a V16 BRM, my all time favourite engine noise scream...

Regards,
John.

[kaleuclint]

Sorry - that should be 'Biopower'; think Ecopower is Opel...
Running on E85 the BioPower 2.0t engine produces at least an additional 18 kW* (147 kW vs 129 kW*) and an extra 35 Nm* of torque (300 Nm vs 265 Nm*) compared to running on regular unleaded petrol.

Your are right though John; the best long distance seats of any car, but the handling of a shopping trolley ... except in the snow

[johnl]

Your are right though John; the best long distance seats of any car, but the handling of a shopping trolley ... except in the snow

I haven't driven the Saab for a while because I've been using the Alfa. But I drove it last night when a bit too tired and nearly ran off the road on a corner, the Alfa does not understeer like that...

Still, on a long distance highway cruise the Saab is rather nice.

Regards,
John.

[johnl]

Third day on 98 for the Saab. Computer says less fuel per 100km, but not a lot less and experience with the car suggests the reading will creep up over the next few days. It's certainly not a dramatic difference as with the Alfa. I suspect the difference may be due to the Alfa having a relatively high compression ratio, but the Saab (being turbo) having a much lower CR. The lower CR would very likely be less efficient at light throttle openings, i.e. cruising.

Regards,
John.