HE V12 is it ok to use 95 octane unleaded

[Yeldaw]

Hi my series 3 is fitted with a HE V12 engine is it ok to use 95 Octane unleaded. The local supplier is stopping the import of super unleaded

[MarekH]

If you think you have a problem, you can always alter the overall advance by rotating the distributor.

kind regards
Marek

[42south]

I had the same problem in New Zealand with fuel supplies. I don't think there is any problem with unleaded 95 octane. The valve seats are hardened already.
I run my pre he on 95 with no problems
I think as marek mentions you should get your timing adjusted

[Yeldaw]

I thought I would gradually reduce to 95 octane by filling up half and half with 95 octane and 98 super unleaded and so far have not noticed any issues with detonation. I will fill from half way again with 95 octaine and see if I notice any issues. Fingers crossed it is going to be OK

[42south]

I think , don't quote me, that the 95 is a faster burning fuel, thus the need to alter your timing.
My pre HE is on 8 deg BTDC, and it is an ex UK car.
I hear no sound of pinking even under hard acceleration going uphill.

[PeterCrespin]

I think , don't quote me, that the 95 is a faster burning fuel, thus the need to alter your timing.

I won't quote you, because it's rubbish. So that's alright then! :-)

Pete

[MarkE]

The lower the octane rating the higher tendency to ignite prematurely causing knocking...so I think Mark that lower octane petrol does burn more readily, if not more quickly.

But when it comes to V12 engines and what they can happily use....anything! I accidentally put a gallon of paraffin in my empty xjs after a winter snooze (me and the car). Realising my error on completing the task, but in a hurry, I added a couple of gallons of petrol to the tank. The car ran well to the petrol station, about 20 miles or so, but was a bit smoky!

Diluting it further with another 17 gallons of petrol and all was fine.

[42south]

I think , don't quote me, that the 95 is a faster burning fuel, thus the need to alter your timing.

I won't quote you, because it's rubbish. So that's alright then! :-)

Pete

Perhaps not altogether rubbish pete.
A search on the net shows lower octane fuels do have a greater tendency to ignite faster. There is also some info that they burn faster.
Also modern cars with a knock sensor, and engine mapping ECU, do automtically alter the ignition timing for lower octane fuels, hence my comment.
By your comment you obviously have some specialised knowledge on the subject, I would like to have a definitife answer if you would share.

[PeterCrespin]

Normal road fuels of all grades burn at more or less the same rate. It's actually quite slow and you can see it by eye if you ignite, say, a long trail of petrol or pour it on a bonfire (NOT recommended). It's much faster in an engine because of charge turbulence. The adjustment to timing that can be needed when running on differing fuel grades is due to their varied propensity to detonation, not variable burn rates.

Detonation is a totally different and uncontrolled destructive combustion process compared to normal ignition. An explosion really - hence the 'pinking' sound from deep inside the head. Susceptibility to detonation is denoted by octane rating. Knock sensors work with the ECU to retard timing 'on the fly' if their piezo-electric microphones detect detonation, not an altered burn rate arising from a different fuel grade.

Cheers
Pete

[Woolfi]

Pete is correct.
Regards Wolfgang Gatza