Please explain the difference in fuel consumption then.

 

I know what I measured. The 2 gas stations are 374 km apart, and supply both 91 and 94 grades. Identical road and weather conditions, test runs done 1 week apart. Mountain ranges up to 5000 ft, trip times very similar, average speed over 100 kmh, top speed up to 160 kmh. 91 AKI gave 24 mpg, 94 AKI gave 27 mpg (imperial gallons).

My explanation is that Jaguar recommends 91 AKI as the minimum to avoid engine damage from detonation, and I take that to mean that 94 AKI is even more preferable. Ignition timing changes will protect the engine but lead to a loss in efficiency. In addition, 94 AKI contains 0% ethanol.

Am I right? I think so, you think not, but that's the beauty of this forum. We are all here to share our experiences and seek information. Here are a few comments on this subject:

I will admit that I tried lower octane once.. What I did measure was a reduction in fuel economy. So, any savings gained with a lower per gallon cost was eliminated by an increase in consumption. So, back to premium I went.

I figure the Jag can run on anything you put in there, but it will not run at peak efficiency due to crappy gas. Kinda like if you tried to eat McDs then go run a marathon. You've got the fuel, but is it the right fuel?

Because of the retarded ignition, the engine will, of course, produce less power, and have slightly higher fuel consumption.

...but the engine computer notices this and slightly retards the timing to offset the slightly lower octane. Power is reduced slightly (not noticeable) but fuel economy goes down slightly too. After 3 or 4 tanks of experimenting with 89 and 93 octane (91 is rare in DC) i've found the savings at the pump is offset by the lower fuel economy it gets on 89 octane fuel.


My question to you, regarding your own reported mpg, is "how do you explain that a 9-year-old engine, designed for 91 premium but always run on 87 regular, is able to exceed the US Government mileage rating by 25%?".

 

Love seeing a couple of Canucks going at it.
Surprised after this long the thread is not locked.
another no win topic, like oil, spark plugs and beer.

I suggest Robin and Mikey meet up in Winnepeg, Robin wears a Canucks jersey and Mikey wears a HABS jersey ( I am sure he is a HABS fan) Robin throws down a 12 of Kokanee and Mikey throws down a 12 of Brador
Then they drop the gloves and sort it out like true Canadian boys would.

Question for Robin.
That B doesn't stand for Bachman does it?

 

FWIW I'm paying under $3/gallon, around $2.86, for premium here in CO.

 

LOL!! No it does not, but I'll show you mine if you'll show me yours.

 

The forum is all about discussion and different opinions and as long as we can defend our different viewpoints sensibly and civilly that's fine with me.

 

Both sides will be pleased to know that the hypermilers often ignore MPG in preference to MP$. Miles per dollar.

By doing this they capture the price gaming used to set prices by utility value.

Upon converting to MP$, it is often seen that the cost differential between 87 AKI and 91/94 AKI is not as great as it would seem to be looking only at the price on the pump.

And yes, on vehicles that adjust timing and fueling properly for octane, the higher octane fuel wins on a MPG basis.

Another factor is the lower or eliminated ethanol component as the energy content of a ethanol blended fuel is less than the energy content of non-ethanol blended fuel.

Refiners lower ethanol content on "premium" because it sits in the storage tanks longer. The goal is to avoid the accelerated spoilage brought on by ethanol.

Since the only real reason to be concerned with fuel consumption is cost, then adopting MP$ as a metric is quite sensible. MPG is meaningless unless the dollar component of the equation is captured and tracked.

 

I'm going to pipe in here before the thread gets closed.

Thus far I don't I don't object to the spirited discussion.

It reveals both side of an argument. So let's be civil and let's not jump the gun.

 

Possibly the thread is still running because it seems to be an ongoing topic of interest for many, including new members who drag it back up from the grave for another good thrashing. Despite this the level of confusion, misinformation and myth surrounding octane ratings doesn't seem to subside though.

The post hasn't been locked for the reasons pointed out below by Norri. Most 'Canucks' would be more likely to write their Member of Parliament a sternly worded letter of concern rather than engaging in fisticuffs. I haven't been a Habs fan since the league expanded beyond the six original teams (they play hockey in Florida?) and sadly Brador is a mere shadow of it's glorious past. I'm a hombrewer so there's very little commercially made beer in my house anyway.

Thank you Norri.

Robin.
I presume most of the above was addressed to me, pardon the editing.

Putting aside the confusion about double conversion of Imperial to US gallon and fully taking into consideration ethanol debates, let's concentrate on octane levels.

You maintain that if an engine is operated on less than 91 AKI, two things will happen:

1) cumulative engine damage will occur due to detonation.

2) power/mileage will be noticeably affected.

Evidence to back this up has yet to surface. On the other hand, my point of view is:

a) the circumstances where detonation would be present are few and far between.

b) the knock detectors are very effective in quelling the few instances where detonation is present.

As a result, no one (as yet) can present an example of an engine damaged by detonation. This would tend to infer that points a) and b) would apply.

To further support point b), no one has yet come forward with claims of reduced power or mileage when operating on low octane gas. My own experience is that I achieve the same mileage whether using 87-89-91 or 94. In other words, were I to re-do the same drive as yesterday with any of these fuels, I'd still get 30ish mpg.

Which brings us to this:

Simple. The EPA numbers are derived by the OEM by driving a car over a precisely described series of routes in a tightly controlled manner. What falls out of this is three published numbers, city, highway and a combined rating. None of these numbers is the minimum, maximum or average mileage a car can achieve. It's a consistent repeatable test that all OEMs must perform and in theory allows consumers to compare cars. What you saw in my picture is what I could personally achieve by driving in a certain manner over a certain route using a certain fuel. Certainly this differs from the EPA tests- but so does your own experiments using 91 and 94 AKI.

For the record, I don't always use 87. It's fairly rare in fact and it was used yesterday, as stated above, as there was short term upward bump in local fuels prices plus the fact that I'm that cheap. I regularly give frugality lesson to the local descendants of the original Scottish settlers through hands-on demonstration of how to make copper wire out of a penny.


Now a reworded question to you-

You claim to have achieved 27 mpg on 94 AKI and 24 mpg on 91 AKI. How do you explain the dramatically reduced mileage while on 91 other than detonation being present and the knock sensors 'pulling timing'? If this is true- why is your engine not suffering cumulative damage as per point 1) up above? If either of your points are true, then Jag should have either specified a minimum AKI of 94, or tuned the engines so that no detonation occurs on 91.

 

Detonations come in many forms, am sure there are a couple very destructive, just as well as many that don’t do anything.

As long as one isn't sure what the composition is of the fuel as Plums mentioned, you can't judge it on AKI alone. Also short term fuel measurements don’t mean anything imho there is just so much that can influence the actual consumption, and long term measurements are hard as well as driving conditions must be similar over that period. And this is assuming even all factors are the same (so new clean engine/sensors etc etc).

I can't add anything to this discussion as I have been only focused on burning more fuel, with a side twist to do it as efficient as possible though. Full power AKI surely does make a difference on a highly tuned car (so with less reserves), pulling timing after detonations do have a negative effect on power, but also is a safeguard for the engine.

 

If the discussion is 'octane rating', the only parameter of relevance is AKI. Rightly or not, fuel is presented for sale to the consumer using this sole rating as a guide. As debated elsewhere, there's also a confusing array of names: super, premium, ultra, 5 star, high test etc promoted by the refiners but this just serves their own marketing purposes and nothing else.

This is not say that there are not other variables in motor fuel- quality/quantity/blend of additives, Reid vapour pressure, specific gravity, flame front velocity, energy content, not to mention the 'winter/summer blends', but none of these other qualities are tied to the octane rating. For that matter, neither is the ethanol content, but at least mention is now made at the pump in most locations. The much hated E10/gasahol has been in common use for 20-30 years but nobody took much notice till the labels went on the pumps. That says a lot right there.

 

Really? stratospheric national debt with no apparent way out and you are celebrating low fuel taxes? Just keep kickin the can down the road, till the Chinese bankers arrive I guess.

Back on the main topic. I cant really get concerned about the marginal cost of Premium vs Regular gas. Its such a small number compared with the overall cost of buying, maintaining, registering and insuring a car its hardly worth considering. I think its just because its the more visible cost that we see every few days.

 

I have used our 98 Premium for as long as its been available.

All the Jags have used it 100%, regardless of what the book says.

I do not use Ethanol, as it is not common here

Our 98 Premium is running at $1.65/ltr, and it is what it is.

 

And I still use 87 if the mood suits me. Car runs perfectly, just like it always has. This thread was dug from the grave why?

 

i was debating over the price of fuel couple yrs back.

i said what if the price of fuel rose to $20. per gallon , his remark was,"i dont care what it costs,i,m going to buy it, life is to short to worry about things beyond our control"