I know Costco says their gas is Top Tier, and so does AM/PM, tried them, not as good as Chevron, Shell, or 76. As mentioned above, if you must save $5 on a fillup by buying cheap gas, you shouldn't be driving a Rover.

 

Here in TX (my area) it’s a 15.00 difference per tank. It goes 2.09, 2.69, and 3.29 on average. So bigger than 5.00 difference. Then if I go up near Austin it’s 2.19, 2.35, and 2.45. Just depends on the area.

 

Knock sensors do not detect different fuels. All they detect is knock caused by detonation. Detonation only happens when fuel is ignited at the wrong time. The ONLY difference between 87, 89, 91, 93 and other octance fuels is their resistance to detonation. The variation in cleaning additives used varies between companies/stations, not necessarily the octane rating.

The 4.0/4.6 engines are relatively low compression and are not timed aggressively enough to require higher octane fuel, and from what I have read the air fuel mixture is pretty rich anyway. This means you can use low grade fuel, like you stated, even in middle of africa.

I fail to see why people think the lack of an EGR system means it requires higher octane fuel.

On the other hand, I ONLY use 91 or higher in my 2006 GTO because it is a high compression, aggressively tuned engine. I CAN use lower octane in a pinch, but would not give it over a certain amount of throttle as to avoid detonation.

I'd personally like to hear a Land Rover engineer comment on the decision to put a premium fuel only warning on the vehicle. But keep in mind, it says use premium fuel only, doesn't state anything about an octane rating. Basically just states don't use crappy gas. Does anybody actually data log or have the ability to do so to even check if the knock sensors are activating and pulling timing? I really doubt it.

You can use whatever gas you want. But you're throwing money away using expensive gas on an engine that doesn't need it.

 

Just after I got it, I forgot about using premium fuel in my '99 because it was my first Rover and I started filling it with regular instead. Started having misfires, rough idle, and poor performance at low speeds. Highway speeds didn't seem to be a problem but I didn't keep any hard records of mpg and I didn't know the truck well enough to be able to get a perception of how well it was performing under different conditions. This went on for a couple of months, during which time I used fuel from several different vendors including Citgo, Exxon, and Shell.
When I realised that I was supposed to be using premium and filled up with that instead, the problems all went away.

 

Carbon build up = #1 enemy

 

I use regular unleaded but add Lucas octane booster. I don’t se much difference with mpg, but the engine hums and seems to be much more responsive. It’s really fun when you combine this with sport mode and the Kent cam!

https://lucasoil.com/products/fuel-t...octane-booster

 

I've only had 12 Discos, had the heads off of 7, never run premium. typically get 16-17 mpg on the highway. All aluminum engines are not prone to pre-ignition like cast iron because of the heat transmission nature of aluminum. The high octane may have a benefit at high load low rpm conditions, but the transmission tuning and gearing on the Disco means it is almost possible to encounter those conditions. Pre-ignition rarely occurs at high rpm because of the limited time for the flame front to advance. Pre-ignition also rarely occurs on low load high rpm - where the Disco cruises on the highway. Therefore the high octane does not change engine performance in the Disco operating ranges.

 

Currently in my area it’s $1.10 a litre for 87 and $1.40 a litre for 91 at shell
at 94 litres that’s around $30 extra no thanks

I would really like to hear any explanation from the engineers for the reason they wanted higher octane

 

how did the engine look when you took the heads off and you ran 87 ??

 

Every engine I've dissassembled, there is an extreme difference between the build up and appearance.

I agree with Best...of course.