Not on it's own. The additional boost was causing detonation, a predictable occurrence no different than the results of increasing static compression.

Quote avos:

"So proven that the ECU was already pulling the ignition due to knocks, and this probably also happened already a little bit when I had the 512 rwhp pull a while back."

Raising the octane level of the fuel avoided the issue.

The energy content of fuel does not vary from one octane level to another so there is no reason to believe that a higher octane fuel will result in increased power or increased fuel consumption. If owners of stock type-Rs are seeing better mileage as claimed, this can only be caused by detonation occurring when using the recommended fuel. I am doubtful that Jaguar would release cars to market under such condtions.

 

Sure, but it's a completely stock ECU in that car, no tuning.

It goes to show that the ECU does make adjustments to the timing based on detonation, and a higher octane fuel won't detonate so easily, so...you see where this is going right.

 

Personally I doubt that an unmodified naturally aspirated engine will see any significant changes from using a higher octane fuel.

But the situation changes drastically when you have forced induction. Even at factory boost levels, detonation is always going to be a possibility, higher octane can make a difference.

 

This is true- moving closer to the 'ragged edge', but the claimed increased fuel mileage discussed here could only be achieved by the avoidance of extended periods of detonation. Putting reliance on the absolute accuracy, function and long term reliability of the knock sensors would be foolhardy from an engineering point of view.

I have serious doubts that Jag would release such a car.

 

Well, for the record, here's what I think Jag really meant to say, but didn't because it is too wordy:

The ECU has the ability to avoid detonation by retarding the timing, but this ability is limited to xx degrees. With 95 RON fuel, some timing change will be necessary under load, but the limit of xx degrees will never be exceeded. Nevertheless, because some retardation was necessary, the engine will not run at full efficiency. With fuels of higher octane there will be less, if any, need for timing adjustments.

Sorry I don't know the value of "xx". But what I assume is that higher octane fuels run efficiently for more of the time, hence give better mileage.

 

Robin-

If detonation only occurs under load, then no detonation occurs under lesser conditions. Typical street usage of cars (non-racing) means that only a small percentage of the driving is done under sufficient load to induce detonation where the higher octane rating fuel is of use.

A type-R and non-R take the same amount of HP to drive at a constant speed or accelerate at the same rate. There is no reason to believe that the type-R engine would be detonating more than the non-R under these conditions.

If I were just starting out in my working career, I'd develop a system to directly inject a high octane liquid into the cylinders at the onset of detonation and get rid of the knock sensors. Peak performance would be maintained at all times and the car could run on low octane gas under most conditions.

 

Detonation doesn't just occur under load, it can occur for many reasons, not just because timing is advanced or cylinder compression is high, Engine knocking - Wikipedia, the free encyclopedia

 

I get your point Mikey but, as plums has pointed out in post #26, the no-load situation is valid only "down some country lane at low speed going downhill driving like a granny". Other situations will demand more and more load, therefore more and more timing adjustment.

My test was done over 250 miles, covering 2 mountain ranges of 3000 and 5000 feet respectively. Average test speed was 65 mph because of city limits, but average speed on the mountains was easily 75-80 mph. I shudder to think of doing such a journey with 87 RON fuel, and I would love to hear what forum members estimate the mileage difference might be between the 94 fuel that I used (27 mpg) and the 87 fuel that you suggest would be almost as good.

PS: That's 27 mpg (UK) or 22.5 mpg (US)

 

No. Not 3-4 percent. That would fall into "margin of error" territory and hardly worth
thinking about.

I just did the calculation as a percentage. It could be even better if slow was an option.

But, how about 25 percent?

I fully detailed the conditions and the resulting observations in a fresh separate
post so that it is easier to reference. It again lays out the conditions and duration
so that there ought to be no doubt as to measurement conditions and ought to
avoid being discounted as a one time phenomona.

It is at:

https://www.jaguarforums.com/forum/g...rience-115803/


I think he could.

But it would be more informative to all if people waited for follow-up results
instead of attempting to discount or refute the possibilities implicit in the original
post.

An open and receptive mindset is more conducive to learning.

People came round to understanding that the earth only looks
flat. But it wasn't easy.

The pioneers in that one faced the same problem. The hypothesis that the
earth was round challenged the belief system of the majority, and also
presented a danger to the careers of those who had built their reputation
on the flat earth reality.

Now here's an Occam's Razor Moment to consider:

If person A presents an observation supporting a theorem
and person B dismisses the theorem based solely on a
unsupported belief system, then person A has presented
the totality of the evidence in the discussion because
a belief system is not evidence at all. No matter
how loudly or frequently it is repeated.




++

 

similarly, +4.5 mpg(us)

but observed over 20 trips on the same route

https://www.jaguarforums.com/forum/g...rience-115803/

 

Where are the repeatable, multiple and reliable observations showing
that a V8 S-Type yields the same fuel economy on both regular grade
gasoline with ethanol and premium grade gasoline without ethanol?

Surely, if such a result is the obvious truth, then it ought to be
possible that a series of such results could be found to be posted.

Indeed, there ought to be a virtual avalanche of available data for
posting in this thread.

Otherwise, there is evidence of one position and no evidence whatsoever
of the contrary position.



++

 

Most likely in the place as the results that show the opposite. This post was started by an owner who did a single test on only a portion of one tank of fuel. For reasons unknown, there are posters who want to take the results to the bank as proof.

We then switched hats from E10. vs. pure gas for another re-beating of the octane levels subject. Again, we have one and only one poster who claims that using higher than standard octane gives him better mileage, based on one test.

If we then toss out all the data that's been collected on vehicles other than S-types, there's not much left to discuss.

 

Called the station where I got the gas last Tuesday.

It's 91 octane so nothing out of the ordinary here.

So we're talking about just the alcohol being th the variable here barring some inaccurate and undisclosed octane increase in the gasoline being delivered to that station.

 

That's nonsense - in this thread alone Cambo351, plums and Robinb have all reported better mileage with high-octane gas, with plums repeating the test 20 times over. And I have seen numerous other comments in other threads to that effect.

You were quick to dismiss Staatof's original test as "unbelievable" based on the theoretical composition of E10, so we are exploring other possible reasons in addition to the known undesirable characteristics of E10. This is not a good time to develop a persecution complex over octane.

 

You're the only one with a S-type that's made such a claim. Plums asked for V8 S-type data only.

 

Yes but we still don't know how far it goes, meaning it's till possible that at some point better octane rating is a waste.

I don't know where that is?

Does anyone?

I could try much higher octane racing fuel from this list too:
Sunoco Race Fuels | Fuel Comparison Chart

That might provide an answer after numerous trials

But what's the point? I have to drive in the real world which is E10 @ 91 or 93 @ Sunoco.

If I lived in PA I might do better though.

The only staion even remotely close who's selling ptremium in non E10 is the station I used. All the others are Sunoco racing fuel which is not in my budget.

 

Hmm… Hard to believe that S-type engines are that different from other Jag engines. I guess the postings below from the S-Type section are unsupported, not credible and probably wrong:

...and finally, one for Staatsof:

 

And does anybody want me to go through the same exercise dragging out all the posts saying that they see no difference running premium vs. regular? As a rough guess, I'd estimate they outnumber the posts above by at least 2 to 1.

 

E85 is getting more & more popular here, new vehicles from GM are "flex fuel" which means you can run them on regular gasoline or E85, the engine management adapts to the actual ethanol content in the fuel because it can vary alot, say if you put E85 into a half tank of regular.

I've heard from owners of these vehicles that there is a considerable drop in mileage if you run E85, like 30-40%, so the ethanol content in E10 or E15 would have to have some influence on economy, surely....

 

Yes, the reduction in mileage is more or less linear. Ethanol has only ~2/3 the energy of gasoline.

E0 = 0% penalty
E100= ~33% penalty

E10= ~3.3% penalty