Fuel Octane

Since I bought my 1990 Range Rover Classic 3.9 EFI Estate I've been filling it with Esso Supreme-99 Octane fuel, but is it actually mandatory to do that, or is Regular-95 fine?

It runs great with Supreme and has plenty o' power so I'll probably keep filling with that, but I'd be interested to hear otherwise.

Both my RR3.5 and disco3.9 have only run on 95, the octane grade as stated by Land Rover in the owners handbook.

I had exactly the same car on the same year and only used reg unleaded. lets face its expensive enough on fuel as it is!

fett said:

I had exactly the same car on the same year and only used reg unleaded. lets face its expensive enough on fuel as it is!

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True, plus the higher octane isn't saving fuel as the oil companies are keen to state, since older cars don't have knock sensors.

As I said, the old bat (that is a euphemism by the way, I mean it in a nice way, as in very fast!) is running great on 99 so that's what she'll get.

all cars in the UK have to run 95 by law although in some cases you may end up with less performance e.g higher tuned VAG 1.8T or 2.0T engines. when my 3.9 was running I used 97 or 99 RON petrol as I found the engine happier on the higher RON

discool said:

Both my RR3.5 and disco3.9 have only run on 95, the octane grade as stated by Land Rover in the owners handbook.

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Just picked up on this post - I think LR's octane recommendations are more to do with marketing (at the time) than actual technology. I have an '87 3.5efi & over the model years '86 to '88 (inc.) the LR w/s manual states three different RON figures, all for the same 9.35:1 comp ratio engine!

Personally i can't see how the old donky V8 with bugger all compression and bugger all advance (relative terms) would need anything more than 95 RON.

I mean AT BEST mine is making 47bhp per litre. Now think of the amount of cars that make easy double that and run 95 RON. OK, that's all of them!

Currently got a little suzuki in stock, 650cc turbo making 65bhp and it runs 95 RON as instructed, so there's really no need for higher octane in my old clunker!

OK OK additives in the high performance fuels could make the burn cleaner, agreed, but i really cant see OCTANE being the deciding factor, unless you are running way overstock compression...

Cheers

did ya see the new fifth gear about the petrols?

Linky?

lol, it was on discovery this week but doubt its been tubed yet.

point was really that on a modern car v power gave you nearly 5 bhp while bp super plus gave you 0.3 bhp lol

only really worth if it you have to race somone though with the rv8 and its dizzy timing being fixed to a point I dont think its worth it