Dear all,
Here in Cyprus, where I live, there is the normal unleaded fuel, 95 octane and premium at 98 octanes. I fill my F-type with 98 as required by the manufacturer. However, I recently found that 100-octane fuel is available at some gas stations.
Should my engine benefit from the 100-octane fuel? Or shall I stick to the 98?

 

The engine was designed for 91 so anything over that is fine, provided it's quality fuel. Here in MA the highest octane regularly available is 93 and I run that with a Stage 1 tune without issue.

 

Fuel ratings are different this side of the pond and work out to be roughly your values plus 4 or 5. Our standard unleaded is 95-RON, super tends to be 97 through 99 RON - depending on the brand - and then there was a BP 'trackday' fuel available for a while (- checked and it has been discontined in the UK) which was 102 RON and hellishly expensive even by BP (Bloody Pricey) standards. But yeah, the Jag will run just fine on standard unleaded (91 for you, 95 for us), but I have only ever run super-unleaded through mine.

If the 100-RON fuel the OP can get isn't priced really badly then I don't see any harm in running it. Probably a waste of time over and above a good quality super-unleaded though and especially on a standard, un-tuned, engine.

 

We use AKI in the states, you probably use RON? 91 AKI = 95 RON, I think. I’ve not heard there’s a benefit to running higher octane than the engine needs, though better additive package, less ethanol etc might be other reasons to use the higher octane.

 

Yup, we use RON over here. I think it's more like your 91 fuel is our 95-RON, which is standard unleaded

A friend of mine, who worked at Jag for a few years on the design team (he left a couple of years ago), asked the engine peeps about super unleaded, as I asked him if there was any benefit in my f-type. The word from them was simply that the ignition timing advances (or retards, I dunno, he started talking technical mumbo jumbo and my brain shut off ) to take advantage of the fuel. Ergo, it should make a difference. But he might also have been talking bollocks and just trying to make me feel better about using super unleaded

 

@Stuart@VelocityAP would likely know.

 

Sounds like you guys need to subscribe to our Youtube Channel:

 

Short answer if you don't want to watch the video. North American MON/AKI, you need to add roughly 5 points to get to European (and other) RON measurements.

Yes, you *can* run 91AKI or 95 RON fuels and 'get away with it' but any hard use will probably see a lot of timing correction & power loss. Within reason, I'd always use the highest octane possible. 94AKI/99RON. If 100RON is not crazy expensive I'd go for it.

 

Stuart, a follow up question (or two!):
Would your recommendation be different or possibly stronger if you are running a tune, including your tunes?
And possibly stronger still depending on the level of tune, eg Stage 1 vs Stage 2 vs Stage 3?
The JLR stipulated minimum RON for the AJ126 and AJ133 is 95 RON.
I run your Stage 2 tune and have done so for some seven years now, and I have never put 95 (let alone lower) in the tank, I have always used 98 RON and a while back for a couple of years I used 100 RON (but I stopped a few years ago when that servo stopped stocking 100 RON).
I have considered using 95 RON a few times but always decided against it as I did not want to risk reduced power/performance and especially because the price drop from 98 down to 95 is only a few cents per litre.
On a related note, would using 95 RON in a tuned engine result in even greater timing correction under hard use (compared to a stock engine), and lastly a question I have always wondered about but never found a definitive answer for, does the ECU cater for (eg advance timing) on a tuned engine when using 98 or greater RON compared to 95 RON???

 

Our 95 RON seems to be 10% ethanol nowadays, whereas the higher rating seem to either (still) be 5% ethanol or none at all.