Have you also tried it with ethanol free gas?

 

I don't doubt that the valves were burnt but can assure you that it had nothing to do with the fuel or it's octane rating. Did someone change the ignition advance setting?

 

I don't remember, it was so long ago...

 

I think it was ethanol free. I need to go back and confirm. I took a photo and it didn't mention any ethanol.

 

If you have an engine map that can exploit it, higher Octane fuel should give you more power (by advancing the timing for example).

But, unlike the supercharged engine in a 2005 Mini Cooper S (Works, if you insist), the map(s) in the V6 ECU appear to have been set up for 95 RON as the upper limit.

It might be interesting to find out what the recommended fuel is in the Japanese market...

 

I was low on gas after several runs and decided to put some track side 105 in the tank to see if the ecu was pulling any timing on the stock tune. I saw absolutely no difference in 1/4 mile time or speed with the 105 vs standard 93 from a BP.

 

You need to tune for it, the Jaguar factory map is tuned for 91 or 93, putting in 94, 95 or higher will yield no benefits.

If your tuned and your tuned for higher octane then you make more power and you have higher knock resistance, just like if you tune for E85 for example.

 

I mostly agree that higher octane than required won't increase power output.

My slight reservation is that detonation of which octane rating is a measure of resistance to detonation is affected by several factors.

Compression ratio is fixed however with forced induction engines (turbo or supercharged) the effective CR is increased depending on boost pressure..

In UK we mainly have 95 RON fuel although there's some availability of 97 RON and even 99 RON (the latter is E5 - up to 5% ethanol)

Several years ago there was a debate amongst performance car fans as to whether these higher octane and more expensive fuels had any merit.

One company dyno tested a variety of cars with these various standard and high octane fuels.

The results were that there wasn't any measurable differences in output power, with one exception, various turbocharged high performance engines were found to have a small power increase.

Most likely due to the ecu being able to run more advanced ignition timing or possibly slightly higher boost.

 

That is because the ECU reads from many tables to determine how much spark (timing) it can deliver which shall be based from IAT, Knock sensors, maf rate and a load of other parameters. If the octane is the good stuff, say 93/94 or 99 RON for UK readers even with a high IAT it will retard less than say if it was running on basic unleaded here in UK RON 95 or US Octane 91.

So yes putting better stuff in will have a higher resistance to knock which will always keep the relevant sensors happier and thus the ECU give more spark advance within the stock table parameters.

Octane and RON roughly equates too:
87 - No UK equivalent
91 - RON 95 or there abouts (unleaded)
93 - RON 97.5 or there abouts (super unleaded)
94 - RON 99 (Vpower & Tesco99 in UK)


I am sure if you got a VAP tune and requested a race tune for say 100 octane for drag racing they could give you a tune for that or advice whats possible.

 

 

I'll just drop a few comments in this typically charged discussion. As noted already, higher "octane" rating than required more efficiently burns money, but that's about it.

It's not just timing that gets pulled in response to detonation: boosted cars might limit boost below the normal levels. I'm not sure of the knock strategy for the Jaguar, but turbocharged cars I've had worked that way.

Higher rated fuel is commonly available two ways: race gas and aviation fuel. It was explained to me when I was just a pup that "av gas" has additives to prevent carburetor icing at high altitude, but since you're unlikey to be driving at 20,000 feet, best to stay away.

I did extensive logging and record keeping in a naturally aspirated Subaru-based car, and their anti-knock strategy is quite sophisticated. I recorded consistently better fuel economy with the mid-grade than either regular or premium. Here, that means 87/89/91. I've only ever used 91 in the F-Type.

Also interesting is that when California was using MTBE, I would see a 10% fuel economy difference between fuels doctored with ethanol and MTBE with my hotrod motorcycle. The MTBE was worse. It was also worse in every other possible way, so I was glad to see it go, even though we paid at the pumps twice: once to convert manufacturing to it (billion$) and again to phase it out.

 

In stock form, using higher than required octane fuel brings ZERO benefit. As a matter f fact it can reduce performance, as extensively explained by others, higher octane indicates the "resistance" of the air/fuel charge to ignite prematurely. This is usually caused by high compression ratio (I am sorry Unhinged but you are ONLY PARTIALLY correct, your response applies ONLY to naturally aspirated engines, in forced induction engines, the added boost by turbo or superchargers will create act as a higher compression ratio). This can also be caused by other elements, such as carbon deposits in the combustion chamber (includes piston head).

The only way to benefit from higher octane rating fuel is to map the ignition to take advantage of it. Contrary to what most people think and those cool engine models show, the spark plug will not spark when the piston is at the uppermost position following the compression stroke, but a tad earlier. This is generally called the advance angle, this varies based on several factors from engine load to RPM, to throttle position etc. but it is always dependant on the feedback from the ping sensor, a sensor bolted to the heads (usually), that listens for a specific frequency usually associated with pinging (pre-ignition), usually 900,000/(π×0.5 ×cylinder bore diameter

If the spark comes too early, the air/fuel mix (charge) will ignite too early and at best you end up with a destroyed piston head but you can also end up finding the bottom half of your connecting rod out of the side of the engine block... Anyway, higher octane gasoline allows you to advance that spark (before the piston reaches the uppermost position aka Top Dead Center TDC).

Other factors in determining the required octane: shape of the combustion chamber, Cam/valve. You do NOT want to experiment with gasoline octane rating and timing . While using higher octane is generally safer but resulting in performance loss, using lower than required rating leaves you HOPING that the knock sensor saves your engine.

In my case, my car requires a minimum of 97 octane because of the boost level, this is also aided by a water/meth injection system and extensive ECU mapping when the engine is out of the car and on a bench dyno. The best performance is usually obtained using the lowest octane possible that works well with your engine. Turbo engines are a far greater challenge to map properly.