High Octane petrol....

[Tumble]

Though I must say I'm surprised, this does sound possible to me. As I understand it, the engine is most likely to detonate on light throttle openings. If the normal ignition timing is too agressive for 95 ron fuel and the knock sensor retards the ignition quite agressively, it could be that the engine is running in a poor state of tune a lot of the time, hence the increased fuel consumption.

A lot of my driving is around town - purely because there's bugger all space over here to open it up very often... when I took it across last year I did 1000ish miles in a week, mostly out of town, M-ways etc and only filled it 3 times...

[5lab]

Though I must say I'm surprised, this does sound possible to me. As I understand it, the engine is most likely to detonate on light throttle openings.

hmm think you've got the wrong end of the stick there.. from what i know.. you're most likely to get pinging when there is too much air in the cylinders.. thats only going to happen at full/nearly full throttle surely (not talking about dervs here which are obviously different.)

[Rave]

hmm think you've got the wrong end of the stick there.. from what i know.. you're most likely to get pinging when there is too much air in the cylinders.. thats only going to happen at full/nearly full throttle surely (not talking about dervs here which are obviously different.)

Right, well let's not have an argument on the basis of hearsay eh? It's Christmas night and I really CBA to check the wikipedia etc. right now.

Research it and we'll get back to it tomorrow. FWIW, I read a lot of engine tuning manuals when I was filling out my UCAS form to try and get onto Sheffield's Mech Eng degree. See you tomorrow.

[5lab]

I did say 'from what i know'.. i'd be interested to see if i've got it wrong, because afaik pinking/pre detonation is more likely to occur with a higher compression .. ie, a turbo slapped on or a high compression engine.. if you've got an engine thats running at (say) 10:1 compression, then each molocule of air/fuel gets 10x as close to its rivals as it would be normally (expecting that said piston is at atmospheric pressure when at the bottom of its stroke - i think you'd need some form of low pressure turbo to achieve this.. but we'll take it as a granted for now).. now, being 10x closer to its mates creates a lot of pressure, which is a leading cause of pre-ignition (along with heat). if your throttle was only 1/2 open, then the amount of air, in the cylender, at the bottom of the stroke would be 1/2 what it is with the throttle fully open (give or take). that means the air/fuel mix inside would be twice the distance from its neighbour as it would be in the atmostphere. compress this to 10x what it was, and the air is now at 5x atmospheric pressure. HALF of what it is when running full throttle. as a result of this, one of the leading causes of knock (too much pressure) is halfed, and the likelyhood of knock overall greatly reduced..

[Crazy Cricket]

Agree with rave here.

Firstly, pinking is caused by post ignition, not pre ignition.

For an engine to pink, it needs to resonate sharply, it can only do this by a sudden rise in cylinder pressure. Only after the flame front has started advancing does enough heat and pressure exist for the remaining unburt mixture to flash over.

Rave is right, I feel in saying that an engine is more likely to pink on part throttle openings. This is because under WOT conditions the engine is going to be running a richer mixture.

[Butuz]

Hmm - ive been running round here like an idiot trying to find myself a tank of optimax - and the shell garages seem to have run out

Butuz

[Tumble]

Funny thing is.. Shell garages here (There's a 4 of them on the Island) don't sell Optimax.. just "Super Unleaded" same thing or just normal stuff with a fancy name?

[Rave]

Rave is right, I feel in saying that an engine is more likely to pink on part throttle openings. This is because under WOT conditions the engine is going to be running a richer mixture.

It's also running (in a modern engine at least) much less ignition advance at WOT, due to the the faster flame front propagation.

[Crazy Cricket]

Indeed, the northstar lump was tweaked with a lower static C.P ratio when it's heads were re-designed because the faster burning chamber allowed it to run more aggresive ignition timing.

[Rave]

Been reading this article like me?

[Crazy Cricket]

Aha you found it, was looking for that earlier! Did read it, a while ago though.

All this talk of pinking brings back fond memories of me old man trying to get the old [MG] B running just so with a lump of hose pipe betwix head and ear! Last I heard was that the old girl is just about ok on optimax

[just_laze]

I put 99RON in my car, unless specified in your manual or on the petrol cap itself, there really is no benefit to putting higher RON in. If you drive a Ford, Vauxhall, essentially a European car, then just put your plain old unleaded in, there's no benefits doing anything else.

[[GSV]Trig]

Well mines a Vauxhall and runs loads better on SUL to plain old unleaded as you put it...

[Lowe]

All this talk of pinking brings back fond memories of me old man trying to get the old [MG] B running just so with a lump of hose pipe betwix head and ear! Last I heard was that the old girl is just about ok on optimax

Sorry, but that had me rolling around laughing

[Crazy Cricket]

Cylinder head human skulls are lousy, naff all heat transfer! Well cylinder head #3 since head #2 cracked block #1, the joys of BL build quality.

[Howard]

Right, I filled up with Premium OMFG Unleaded last night So we'll see if it makes a blind bit of difference to anything after a couple of tanks