Octane rating

[geek]

Apologies. Genuine mistake.

Think I came across a bit pompous there. Sorry.

No worries Nick

I get so frustrated with incorrect 'facts' on this type of specialist forum and here's me contributing!

Am off to sit in the corner for the rest of the day and think about what I did (the wife is also refusing to let me have tea)

[DazN]

I wondered this after religiously using V Power on all my cars I was surprised inside the filler cap it says 91-95 for the S4. I thought all performance engines would benefit from higher octane fuel?

[adsgreen]

I wondered this after religiously using V Power on all my cars I was surprised inside the filler cap it says 91-95 for the S4. I thought all performance engines would benefit from higher octane fuel?

Higher octane fuel doesn't have any more "bang" than normal petrol (in fact, all the additives can reduce it). However, with fuel that is more stable under pressure and temperature it is more resistant to knocking allowing the optimum ignition advance. Fuel burns at (for all purposes here) a constant speed so the optimum timing is to have the mixture fully ignited at top dead centre and as such this is almost completely dependant on RPM.
However if the engine isn't knocking under any circumstances then you won't get any benefit from higher octane - the timing will be at the appropriate for the rpm.
So if with the S4 even though it is forced induction there is no part where the engine is retarding ignition due to knocking then you won't see anything.
This is quite possible based on the above as it appears the stock S4 is in a very mild state of tune. Once you remap and fiddle a bit then yes, I would say 460hp+ would cause a few knocks with 95 ron fuel so there would be benefit.

[xxx_mojo_xxx]

Gooble-di-gook

[Damon68]

If you go stage 2 MRC you have to use 99 according to Doug at MRC. I've been using it since the tune but I have to say once or twice I've had to use 95 as 99 was not available and I've not noticed any difference.

[spr0cket]

Been running stage 2 for over a year with 95 every fill up. Though I had Doug map it accordingly so not sure if that's the difference in his advice?

[S4WON]

Stock S4, simple answer is 95