[Tom]

Found in the manual for my 2.6 GSi (Y26SE) these figures:

Octane requirement (RON) 2)

Unleaded- 95 *3
or unleaded- 98 *3
or unleaded- 91 *3 *4

*3) Knock control system automatically adjusts ignition timing according to grade of fuel used (Octane number).
*4) Slight reduction in engine power & torque if 91 RON is used.

Now, going on note number *4 above, if that's the case- Does that mean power and torque are INCREASED if 98+ RON fuels are used?

My opinion- the V6's do like the higher octane fuel, and it seems to make them run much smoother. That's all I ever run my old 2.6 SRi on, and I'm planning to do the same with the GSi once I've serviced it (New fuel filter etc).

What's your opinions on different octane fuels? Someone said Tesco do the highest RON fuel.. is that true? I normally use Shell Optimax myself.

[Dahmich]

tesco USED to have the highest RON but texaco are doing it in some areas. Has been said that supermarkets keep the price of the petrol down due to not have additives in the petrol to help the engine, whereas shell, texaco etc has.
My old Gsi and the Golf both run better on higher ron (and keeps the inside of the engine a little cleaner thus more mpg) but you get what you pay for!

[Tom]

TBH I never knew Texaco were still around lol. I'll need to have a hunt around for one.

Someone also said that the higher the RON, the less it keeps (It basically goes off quicker than lower RON fuels), so he said you're best going to a garage that sells high RON fuel, but make sure it's somewhere that sells a LOT of fuel on a daily basis (Like a main Tesco's filling station) as their turnaround will be more.

True or not?

[Dahmich]

ive never heard of petrol "going off" lol

[Tom]

	Quote:
	Originally Posted by Dahmich ive never heard of petrol "going off" lol

OK Maybe 'going off' isn't the correct term to have used.

Maybe the kind of effect you get when you pour a glass of that lemon juice (The one you dilute with water), then leave it sitting for about 12hrs- it goes cloudy at the bottom, but clear on the top. Think maybe the additives settle or something like that?

I dunno maybe I never understood what he was saying fully

[Dahmich]

tis a good question i wouldnt mind knowing the answer to!

[Leeky]

Shell Optimax does go off. It has good additives, but if stored in tanks that arent filled very frequently the octane rating does lower.

If you use any high octane fuel get it from somewhere that gets serious traffic daily. You'll guarantee the fuel is fresh, the fresher it is, the higher the octane.

I can't speak for other fuels, but Optimax is standard 95RON with additives, and octane booster. When produced the octane rating is around 98RON, but this degrades very quickly.

The much better solution would be to use 95RON unleaded, and every tank fill, fill it with octane booster to bring it around 98-99RON. It'll probably be cheaper too!

[Tom]

Isn't that octane boost stuff pretty expensive though? I remember it was all the hype years ago, when it supposedly 'added upto 20BHP' lol. iirc it was about £20 a shot then not sure about now.

[Leeky]

	Quote:
	Originally Posted by Tom Isn't that octane boost stuff pretty expensive though? I remember it was all the hype years ago, when it supposedly 'added upto 20BHP' lol. iirc it was about £20 a shot then not sure about now.

The cost of Optimax is also very expensive Tom. I'd go with unleaded and octane booster everytime.

You don't always need a full bottle to every tank full either. The obvious disadvantage here is you need to fill your tank to the rim every fill. Whereas just using Optimax/Super unleaded/Tesco 99RON you just put what you want in the tank.