[insane79]

Hi guys,
I have just bought a 325i e90 2009 model, its the 2.5ltr one, which octane fuel do i need to put? over here we get 91 or 97 octane, which is recommended?

Thanks..

[sbce90]

97, Just put in whatever the highest one available is.

[pavo335]

The higher the better

[Ethanderall]

Originally Posted by pavo335

The higher the better

Australia and the US use different octane rating systems... in Oz we basically have 3 levels, 91, 95 and 98 "ron". The US 85 is equivalent to Australian 90 ron fuel and your 91 is equivalent to our 95.

On a normally aspirated engine, there is no benefit to running fuel with an octane rating over 95 (91). The slower burning characteristics of higher octane fuels will provide no additional performance or economy over middle level fuels and, in colder climate areas, low octane fuel can be used with no performance loss as the higher density and colder charge helps eliminate detonation that would be controlled with higher octance fuel in warmer areas.

335 owners on the other hand, should run the highest octane fuel they can find as the much higher compression pressure levels will cause the ECU to retard the ignition timing to reduce the detonation caused by fast flame fronts in the cylinder.

[Dec540]

Originally Posted by Ethanderall

Australia and the US use different octane rating systems... in Oz we basically have 3 levels, 91, 95 and 98 "ron". The US 85 is equivalent to Australian 90 ron fuel and your 91 is equivalent to our 95.

On a normally aspirated engine, there is no benefit to running fuel with an octane rating over 95 (91). The slower burning characteristics of higher octane fuels will provide no additional performance or economy over middle level fuels and, in colder climate areas, low octane fuel can be used with no performance loss as the higher density and colder charge helps eliminate detonation that would be controlled with higher octance fuel in warmer areas.

335 owners on the other hand, should run the highest octane fuel they can find as the much higher compression pressure levels will cause the ECU to retard the ignition timing to reduce the detonation caused by fast flame fronts in the cylinder.

Interesting answer. I've always just used the best fluids I can get my hands on at the time, be it fuel, oil, coolant etc. There usually isn't a big price difference so why take the risk? That's my motto at least.

[Ethanderall]

Originally Posted by Dec540

Interesting answer. I've always just used the best fluids I can get my hands on at the time, be it fuel, oil, coolant etc. There usually isn't a big price difference so why take the risk? That's my motto at least.

...and there's no problem with doing that... but currently the difference between 95 and 98 at the few local servos near me is around 7-10 cents per litre.

The common misconception about high octane fuel is that it's somehow "better" than the lower octane fuels. If you drive a high performance vehicle that has abnormally high compression ratios, OR, you're running forced induction via a turbo or super-charger, you WILL notice better performance on 98 as you would over 91, but not because the fuel is "better".

The octane rating of a given fuel, is the measurement of the speed at which it burns, the higher the number, the SLOWER the fuel burns. Thus if you put 91 in your 335i, under hard accelleration when you're running probably 20+ degree's of ignition advance, the cylinder pressure level of the burning A/F will peak a long time before TDC causing the piston to "rattle" briefly before it goes over TDC and begins to travel downwards. Essentially, the piston is trying to compress the rapidly expanding A/F mixture slowing the pistons travel and robbing you of power.

Your ECU will pick this 'knock' up within 1 or two revolutions of the crank, long before you notice it, and quickly retard the timing until it senses the knock has disappeared. This is great for your engine, but not great for performance.

Running 98 in the same instance has the A/F mixture still burning and the cylinder pressure not peaking until just after TDC meaning that all the energy (well about 20% of it) is used to push the piston down making lots of lovely HP!

[insane79]

Originally Posted by Ethanderall

Australia and the US use different octane rating systems... in Oz we basically have 3 levels, 91, 95 and 98 "ron". The US 85 is equivalent to Australian 90 ron fuel and your 91 is equivalent to our 95.

On a normally aspirated engine, there is no benefit to running fuel with an octane rating over 95 (91). The slower burning characteristics of higher octane fuels will provide no additional performance or economy over middle level fuels and, in colder climate areas, low octane fuel can be used with no performance loss as the higher density and colder charge helps eliminate detonation that would be controlled with higher octance fuel in warmer areas.

335 owners on the other hand, should run the highest octane fuel they can find as the much higher compression pressure levels will cause the ECU to retard the ignition timing to reduce the detonation caused by fast flame fronts in the cylinder.

Thanks for the info, i am not from US, i m from India(asia) over here we get the same european engines in our cars, like the 325i get the same 2.5ltr 270nm torque engine like in europe, over here fuel rating is 91 & 97 octane, so i m better of putting 97octane fuel for this engine?

Thanks..

[insane79]

just found this link, where the review person speced 91 ron for the 325i, check here-
http://www.caradvice.com.au/23283/20...iew-road-test/

whats are your thoughts guys?

Thanks..

[pavo335]

IMHO always get the best fuel you can!

[Kiwi Peter]

Originally Posted by insane79

just found this link, where the review person speced 91 ron for the 325i, check here-
http://www.caradvice.com.au/23283/20...iew-road-test/

whats are your thoughts guys?

Thanks..

You should use your 97 rated fuel

[dizzy_7]

Ive been told to BP 98 is the best on the market.

I only ever fill up at BP for this reason.

Something about how the 98 is refined... i didnt listen to hard just followed suit.

[insane79]

hmmn, guess will just put 97 then..