Plums have you seen united now have 100 octane fuel? I'm really not keen to run water through

 

Denis Brain (before he wrote off himself, TR2 and a very fine French Horn)
got off a speeding charge by telling the judge that the exhaust note was definitely B flat whereas, had he been exceeding the limit, it would have been C or higher.

 

No. But if you dispatch a pair of cruise tickets, pick us up at the harbour and drive us up to Grant's ... I would be glad to personally survey the situation

Before the North American readers get all wound up .. Australia expresses octane on a RON basis.

Water is always the way it has been done. Conveniently enough, the motor under consideration is 6 litres in displacement. So, at 1000 rpm, it is moving about 100 litres of gases through per second. If you add even 1 litre per second, that is only 1 percent of the swept volume.

The procedure is to twist the throttle to a comfortable fast idle, introduce just enough water into the intake stream for the engine to start to labour at the same throttle setting. If you can maintain the rate of flow keep going, otherwise reduce water flow and let the engine recover and repeat.

The method of introducing the water depends on your intake setup. For example whether it is injected or carbureted, and whether downdraft or sidedraft. On an injected engine, one method is to drill a hole in the duct and dribble water through a hose inserted in the hole and supplied by a suspended container.The hose can either be gravity fed or suction fed.

The actual work that the water does is to turn into steam during the combustion phase and steam clean everything downstream of the intake valve. A certain amount of cleaning will happen at the immediate area of the intake valve due to reversion during overlap on the cam. You can at least partially confirm this by pulling a plug for examination prior to the exercise and pulling it again afterwards.

Running it at idle for several minutes after the exercise would be a good practice to ensure that the cylinder wall film is restored before shutdown.

 

Then JF must arrange for the Rev to make a video to record it for posterity.

 

I'll tell you what mate if you organise the tickets I'll gladly pick you up

 

Sufficient to assure myself that there were no carbon deposits of any consequence

Obviously- and no such claim or assertion was made. (?)

That would be approx. 95-96 AKI here in North America. What vehicles do you have in Oz that would require such high octane ratings?

 

Mickey very few vehicles actually REQUIRE a high octane fuel.

But high octane fuels burn cleaner and more efficiently.

We have be knownrun plane fuel 100/110 octane through boats and you do actually notice an improvement in performance.

Also personally I don't run anything less than premium through the jag. Kinda figure it'd be better for it. I can't see the 100 doing any damage it may infact do good. Where's the harm?

 

Not to go off on another tangent, but neither of the above statements are true. Octane rating of a fuel is simply a measure of how well it resists detonation. Nothing to do with cleanliness, additive levels, efficiency, burn speed, energy potential, higher/lower peak combustion temperature or any of the other common myths. Note also that automotive fuels are not rated in the same manner as avgas to establish octane ratings

Running a higher octane fuel than that required to avoid detonation is just a waste of money- but as always, it's your money.

 

Running a higher octane fuel than the engine can use is the threshold some people prefer. This is a consideration when an engine with a ECM that varies timing according to conditions can use a range of fuels of varying octane ratings.

The increased cost of the higher octane fuel is offset by the greater MPG achieved when running the higher octane fuel. Thus the greater per gallon cost is amortised over a greater number of miles per tankful. Depending on market conditions, the differential calculated as dollars per mile may be greater or lesser than parity.

There is a known condition in the latest generation Corvette engine management software where the maximum power can only be achieved after reset. The maximum spark timing allowed by the engine management software will be maintained only so long as the owner is careful to always refuel with the highest octane fuel. If car is refueled with a tankful of lower octane fuel, the engine management system will lower the allowable maximum spark timing. Even if the car is then refuelled with high octane, the engine management system will keep the allowable maximum spark timing at the lower level. The only recovery path is another reset.

Jaguar engine management systems do not suffer from this behaviour. If a Jaguar is fueled with a higher octane fuel, the engine managment system will use more spark timing up to the level where knock is detected using an adaptive algorithm. A Jaguar can be driven using the minimum octane requirement for the conditions, but the same vehicle can be operated on a higher octane fuels and see a benefit in consumption and power production due to the availability and utilisation of greater spark advance.

Observation of the above behaviour requires about two tankfuls on the switch from lower octane to the higher octane. Under those conditions, a difference can be observed switching from 87 AKI to 91 AKI.

 

Also the HE V12 down here is 12.5:1 comp ratio.

My findings, and as about as scientific as you will EVER see from me.

This was done many years ago, before my venture into Foum life, and purely from my own trial and error, nothing sinister involved.

I ran one of our HE's on our 91, OK, but a tad off colour performance wise, NO detonation.

Next tank. our 95, better, not so sluggish, and a crispness to the exhaust note (not standard system), and NO detonation.

Next tank, our 98, mmmmm, luvs this stuff. Crisp note, instant oomph, just all round a "sweeter" sounding, and feeling engine.

Much later in the life of the car, I got caught with a tank of Ethanol 10%, DID NOT like that at all, NO "sting", really off song, as I say. Drained it, good weed killer (environmental vandal that I am), refreshed with our 98, took a few kms to settle, but OK, never got caught again. Luckily this Ethanol stuff is a rarity where I live.

We once had a BP here with "100 Avgas", and the drag boys were the prime customers, its gone now, and I never tried it.

 

The behaviour Plums has mentioned on the latest Corvettes is common to the Camaro and I believe some other GM products. Seems like a strange way of doing things- but...............

The point raised above (to clarify) is if an engine is operating detonation-free on a given fuel- meaning that the knock sensors and software are not intervening, increasing the octane level beyond that will not result in additional power or mileage.

 

Agreed 100%.

BUT, the car in question has NONE of this technology.

This stuff all works for my X300, S type, and your XK8.

My V12's all needed to be timed VERY carefully, and YES, when our 98 fuel was used the timing could be "tweeked" a tad in the advance direction. The XJ-S could go about 5deg more advance than with our 91.

Those were the days when the driver had the RESPONSIBILITY for his car/engine, and I liked it that way. This new stuff is all "great" as long as it works as and when required, if not, LIMP mode usually, no fun in that, but that is technology for as all.

I like my MK10, all of 3 wires for the WHOLE ignition system, and NOT a computer in sight, and if it stops, file the points, reset the gap (usually by eye), drive on, and of course the obligatory SMILE, ITS A JAGUAR MATE,HAHA.

 

Anyways guys figured I may aswell bight the bullet and give it a shot ultratune are doing it. It'll cost $200 and is getting done on thursday I'll keep you posted as to the results

 

Ok so I'vee had it done. I've noticed a slight increase in power nothing significant. But she is running a lot smoother. All in all I am satisfied with the results

 

The point of bringing up the Corvette/Camaro behaviour was to illustrate that engine management systems adapt to fuel octane. In that specific unfortunate case, the adaptation is downwards only. Recovery requires a full reset.

However, where the engine management systems is sophisticated enough it can go beyond your second paragraph above.

The adaptation will push timing to the upper edge based upon any number of factors, but most importantly the knock sensors. The result is that most Jaguar V8's will run on the full range of commonly availabe pump grade gasoline without knocking. That does not mean that the knock sensors are or are not "intervening", they are simply "reading" and the ECM is "adjusting".

Given the "intervention" or "adjustment" and a comparison of 87 AKI versus 91 AKI on a engine with a management system capable of advance as well as retard adaptations, the octane will be used to its maximum potential. The pre-determined, programmed increased advance on 91 AKI results in increased efficiency purely as a result of the increased advance, certerus paribus. Depending on the task, that is either improved fuel economy or increased power.

A further observation seen under long term OBD-II instrumentation is the decrease in LTFT when fueled with 91 AKI as compared to being fueled with 87 AKI. This is directly correlated to increased fuel economy. Of course, whether the increased fuel economy overcomes the price penalty is dependent on the price premium. In any case, the use of "premium" fuel in preference to "regular" fuel is not quite as costly as people might think due to the mitigating factor of improved fuel economy when the final "Miles Per Dollar" figure is calculated.

Yes, there may be a point where further octane capability yields no benefit ... but, that point is at an octane level that is beyond what is normally available at consumer level fuel stations.

++

 

Yes, it well known that power/mileage can be inhibited through the use of lower octane fuel. This has been beaten to death on this forum. Is there any data available to demonstrate that the more modern Jags are running at less than optimum timing with the factory recommended octane level of fuel? Possibly we should follow forum guidelines and stop hi-jacking other's posts. As mentioned by Grant, the point is not relevant to the OP's car or his questions.

Steve- glad you got some return on your investment. Please keep us posted on the long term results.