I'm curious to know if the computer will try to advance timing if higher rated fuel is used. Has anyone tried 100 or 110 octane fuel in their F type?

 

My understanding is race gas will potentially contaminate oxygen sensors - and our cars have 6 of them!
The engine software is programmed to optimize the fuel injection by listening for ping, every 2nd or 3rd trip more than a certain distance and speed and it will do a cylinder-by-cylinder check for ping.
Assuming you don't kill the O2 sensors, it could take 2-3 trips of 10+ miles at speed to take full advantage of the new fuel.

 

Yes, a lot of various racing fuels contain metallic additives (even if unleaded). However, some, though still not street legal, are specifically formulated without those compounds to avoid damage to sensors. Sunoco 260 GTX is one such fuel with a 103 research octane and a 93 motor octane resulting in a 98 pump octane ([r+m]/2).

 

Cars do not have devices to detect octane levels directly. They rely on the presence of detonation (knock/pinging) detected through the knock sensor and adjust timing and fuel mixtures accordingly.

If the cars operate knock-free on the recommended fuel (91 AKI/95RON), which I believe is true, then going for higher octane will achieve nothing other than emptying wallets.

 

I did it when I tracked the car for the heck of it. Didn't do any damage, not clear it did any good either. I'm not a good enough driver to make use of the difference if there was one. It was an impressively expensive fill up though.

 

I haven't looked at the programming of Jaguar's computers, but have done some study elsewhere. In general, a "tune" is for a particular kind of fuel. When detonation is detected, the ECU will alter operation to try to eliminate that by backing off on available parameters (e.g. timing).

Performance is reduced if conditions are not optimal for the tune, such as lower quality fuel, but performance won't be increased if the fuel is better.

EDIT: For those interested in how this is done for Subaru, perhaps the most widely understood, check out this article. It even points to a more detailed one, but this is a good starting point.


<a href='http://a href="http://www.romraider.com/RomRaider/HowToUnderstandKnockControl" target="_blank"http://www.romraider.com/RomRaider/HowToUnderstandKnockControl/a' target="_blank">RomRaider - Open Source ECU Tools | RomRaider / How to Understand Knock Control

 

That's not always entirely true

The premium fuels which tend here at least to be 98 RON burn more cleanly and more cometely so it may not give you a heap more power but is likely to give you slightly better fuel economy and also help keep the upper cylinders cleaner. Most people who know their stuff recommend using the highest octane that is within the manufacturers range, I wouldn't suggest using race fuel, but premium fuel at the fuel station then yes.

 

Don't forget that the measurement scale in the US is different to many other parts of the world. What's sold here as say 93 using the US scale is equivalent to around 98 using the measurement scale used in certain other countries.

 

Sorry, that's nothing but misleading advertising that's brought you to that conclusion. The octane rating of a fuel indicates the resistance to detonation and nothing else.

The only difference between the lowest and highest octane fuel is the additive package. The gasoline/petrol they're added to is the same base stock.

High(er) octane fuels may or may not have more cleaning additives but modern engines burn the fuel completely without the need for complex additives anyway. All brand name fuel has sufficient cleaning additives to ensure that no carbon build up occurs.

Your statement infers that the 95RON fuel recommenced by Jag does not contain enough and is operating in a contaminated state. There's no evidence to support that.

 

Hypothetically, the ecu will always try to run as much ignition advance as it can without pre-ignition in order to maximise efficiency. So higher octane fuels ought to mean more advance. Could make a difference...

 

Only up to the limit of the tuning, and the tuning probably is not optimized for octane ratings above commonly available "premium" fuel.

 

True... though the various aftermarket tunes can be set against whatever octane level you prefer.

 

You mean detonation, not pre-ignition.

The ECU will attempt to run full ignition advance limited by the factory setting. The factory setting equates to the advance possible by the recommended fuel, in North America that would be 91AKI.

To do as you suggest would mean that the engine would always be in a constant loop of detonation/knock sensor kicking in/advance being pulled/detonation stops/re-advance timing/detonation/ over and over.

There's also the factor that engines do not necessarily make more power with increased ignition advance. At a certain point, the expanding gasses will actually attempt to push the piston backwards in the cylinder as it's still rising on the compression stroke.

This can easily be seen in a Gen 1 Chev small block which reaches peak power at 36-38* advance. Going further, even if detonation does not set in, will see decreased power at 40* advance and higher.

 

Well I didn't get that from advertising, it came from someone with a lot of technical race engine experience, but whatever.

 

I think that pretty much sums it up, at least for the system with which I'm most familiar: If the knock sensor is activated, the system pulls some timing. This happens each time the knock sensor is active up to a retard limit. The return is not immediate though. When a specified time period lapses with no activation of the knock sensor, timing is nudged back up. This continues until the advance limit is reached or knock is detected again.

Lather, rinse, repeat.

 

Mikey, one of my jobs, many years ago, was to calculate and specify the precise blends of various components to produce the specific grade (octane rating and distillation characteristics) of gasoline. Butane, light raffinate, light catalytic gasoline, heavy cat gasoline, heavy reformate, and alkylate were combined at specific ratios to produce the desired results. The specific grades were shipped by barge, ship or pipeline. Some additives were added at the refinery, and others added at the terminal. So, no, all gasoline grades don't come from the same base stocks, just the same components.

 

Fair enough, but the point is that aside from additives and octane rating, 'high' octane gas is essentially the same net product as 'low' octane gas and that claims of burning more cleanly or more completely is pretty much advertising fluff.

 

Octane has nothing to do with how cleanly the fuel burns, it has to do with how quickly is burns and the flash point.

Stolen from somewhere on the internet... A pretty good explanation IMO...


"Compression and Horsepower
Lower octane fuel burns faster and has a higher flash point than higher octane fuels. 97 octane has a lower flash point and burns slower than 87 octane fuel. A typical four-stroke engine sucks in fuel and air – usually a 14:1 mixture – on the intake stroke. The next stroke is the compression stroke. The piston starts moving up in the cylinder, compressing the air and fuel and building pressure.
As the piston reaches the top of the compression stroke, the fuel and air has been compressed and the combustion stroke starts. As the piston reaches the top and starts going back down, the fuel and air mixture burns. This is where the difference between higher and lower octane fuel comes into play. The last stroke is the exhaust stroke – unburned fuel gets pushed out of the exhaust valves and into the exhaust system.


A vehicle with low compression requires a lower-octane fuel because it does not build enough pressure in the cylinder to create enough combustion to efficiently power the engine. Thus, using fuel with a higher octane or racing fuel (110 and higher octane ratings) is a waste of money because the engine will not run as efficient as it will with the lower octane, which is more explosive than the higher octanes.


If you have a high-compression engine, such as in a street rod or a racecar, you will need a higher octane fuel to slow the process of burning the fuel to create energy and horsepower. An engine with 11.5:1 compression with the ignition set at 32 degrees advanced makes more horsepower using 110 octane than it does using a lower octane fuel, but actually loses horsepower if you try to use 114 octane. It simply does not create enough pressure in the cylinder to efficiently burn 114 octane fuel."

 

I am so enjoying this thread.

Occasionally people admire the car and ask me "how many horsepower?" Or "V6 or V8?"
I sometimes tell them (if they are not car guys) "I don't know; the F-Type is fitted with a 450 kilowatt fusion reactor" and I slip away leaving them to wonder...

 

But unfortunately wrong. Octane rating has nothing to do with flame front velocity (how quickly it burns).

To say so as per the quoted text suggests a lack of understanding of the detonation phenomena.

This might help:

Whitfield Oil Company Flame Speed, Octane Number & Horsepower

Octane is not how fast a fuel burns