Carbon buildup - should I use 100 octane fuel on my 2009 35i Z4 ?

[louisodwyer]

Hi all,
I have a beautiful 2009 35i Z4, 7-speed gearbox, with 48,000 kms.
I have been reading lots of disturbing articles about carbon build-up on the N54 engine intake manifold and what to do about it.
I don't know if I have any build-up at 48,000 kms and certainly the engine is running like a charm.
So, three questions:
Should I use 100 octane fuel to try and slow down the carbon build-up, or is that a myth?
Would 100 octane fuel be better for the engine anyway or should I stick to 98 octane?
Lastly, I've heard of fuel additives that can slow down the carbon build-up. Can anyone recommend if these should be used or not, is there any reason not to use them and have you any recommendations for a specific brand?
Many thanks!

 

[Anonymous]

Hello, non of the above will have any effect on the matter with your engine in terms of 'clean up'

The fuel is directly injected into the cylinder bypassing the inlet manifold.

Therefore no matter what you do to the fuel its not going to affect the carbon buildup in the inlet tracks...that's why it can be a problem.

The reason why the carbon builds up primarily is due to oil fumes from the engine being recirculated via the engine breathers into the inlet (unlike the petrol)...with no fuel vapour to wash the oil deposits away they get oxidised in situ and start to clog up the inlets..

The N54 engine as an early design for BMW for direct injection is worse than later designs..

Some people fit an oil breather catch tank to try and remove this issue..

Unless the car has been modified to exploit higher octance fuel BMW designed it to run on 95 octane and achieve stated performance.

There is little evidence to suggest any benefit for most people except placebo given how powerful the car is to start with..

Others may add / /expand on this I'm sure..

 

[MACK]

Just stick to 98/99 octane.
It's the additives rather than the octane that would have the cleaning effect really. But as Pbondar said with direct injection these won't help keep the air intake or inlet valves clean. But that said, as the higher octane fuels tend to have more additives it will help other bits such as the injectors etc.

 

[PDJ]

To get the gains from higher octane fuel you need to have a compression ratio above 12:1
Also the pump fuel that is higher octane is only rated to say at that octane for 14 days, race fuel is guaranteed to stay stable for longer.

 

[mcbutler]

Hi all,
I have a beautiful 2009 35i Z4, 7-speed gearbox, with 48,000 kms.
I have been reading lots of disturbing articles about carbon build-up on the N54 engine intake manifold and what to do about it.
I don't know if I have any build-up at 48,000 kms and certainly the engine is running like a charm.
So, three questions:
Should I use 100 octane fuel to try and slow down the carbon build-up, or is that a myth?
Would 100 octane fuel be better for the engine anyway or should I stick to 98 octane?
Lastly, I've heard of fuel additives that can slow down the carbon build-up. Can anyone recommend if these should be used or not, is there any reason not to use them and have you any recommendations for a specific brand?
Many thanks!

Fit an oil catch can from Mishimoto. Excellent product and a complete kit for the N54 is available.

https://www.mishimoto.co.uk/bmw-n54-baffled-oil-catch-can-kit-07.html

My fitting guide is here https://z4-forum.com/forum/viewtopic.php?f=23&t=119149&hilit=oil

 

[louisodwyer]

Hi Mark, many thanks for that info.I have read about these catch cans but didn't realise they were that easy to fit. Basically you are replacing the breather hose with the two catch can hoses?
Can I ask you what drain kit you used?

 

[louisodwyer]

Hi Mark, me again... I had a look at my engine and the pipe you are talking about (breather pipe/vacuum hose?), I've circled it in the attached pic.
You said you had trouble taking it off and broke the clips - could you not just cut it off? It looks like the new hoses for the catch can are secured with tie wraps/jubilee clips?
Also, did you have to move the hoses on top out of the way? (I've circled the clip holding one of the fittings to the strut) Was that difficult?

 

[sunnydays]

Hi Mark, me again... I had a look at my engine and the pipe you are talking about (breather pipe/vacuum hose?), I've circled it in the attached pic.BMW catch can.jpg
You said you had trouble taking it off and broke the clips - could you not just cut it off? It looks like the new hoses for the catch can are secured with tie wraps/jubilee clips?
Also, did you have to move the hoses on top out of the way? (I've circled the clip holding one of the fittings to the strut) Was that difficult?

You should be able to remove the vacuum hose with out breaking the clips. It is a little difficult, but take your time with it, and it will come off.

Regarding the brace / plastic mount above they are easy to remove. I would remove them for accessibility. Should only take 5 minutes.