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  Reply # 2089345 12-Sep-2018 14:38
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kryptonjohn:

 

It's confusing. I would have though modern cars would be able to detect knocking and retard the timing to deal with it. However... does that make the combustion less efficient?

 

Also, I have been told that the cost of producing high octane petrol is no way near so much more expensive than the pump price differential... which is there largely for marketing reasons. If so, and if higher octane can be more efficient, then that sounds like marketing considerations are increasing pollution?

 

 

 

 

 

 

Bye bye efficiency and power.. A lot of modern cars do have knock sensors. In my BMW it does have a knock sensor but it just throws a light if it starts to knock. Has not cut power on me when I did that silly fuel up.





 


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  Reply # 2089355 12-Sep-2018 14:59
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I've never tried 91 in my BMW 550i but like Coil I would expect a loss of efficiency and power, it feels sluggish on acceleration.  95 is the minimum for me and that is a trade off between slighting increased power of 98 vs the cost, although never tried.  The car is suppsoed to accept 91 fine but meh it would feel dirty!


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  Reply # 2089652 13-Sep-2018 08:05
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Benoire:

 

I've never tried 91 in my BMW 550i but like Coil I would expect a loss of efficiency and power, it feels sluggish on acceleration.  95 is the minimum for me and that is a trade off between slighting increased power of 98 vs the cost, although never tried.  The car is suppsoed to accept 91 fine but meh it would feel dirty!

 

 

 

 

If it is a Jap import the 91 on the flap might be a bit different form the 91 at our pump. Who knows, I am no expert but you tell me if a high revving high compression performance V8 should be on our cheapest or best fuel?






 


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  Reply # 2089678 13-Sep-2018 08:16
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Oh I don't intend to run it on 91, can't think of anything worse... BMWs are built around 95 as the standard base for their performance, well non-M class models anyway, and I don't see too many issues with running it on 95... I just notice the power loss as its slightly more sluggish but at around 8c/l cheaper over a 65l tank it works out slightly cheaper on 95 than 98; that said I still put 98 in the damn thing and get 400km if I'm lucky.


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  Reply # 2089987 13-Sep-2018 13:02
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Benoire:

 

Oh I don't intend to run it on 91, can't think of anything worse... BMWs are built around 95 as the standard base for their performance, well non-M class models anyway, and I don't see too many issues with running it on 95... I just notice the power loss as its slightly more sluggish but at around 8c/l cheaper over a 65l tank it works out slightly cheaper on 95 than 98; that said I still put 98 in the damn thing and get 400km if I'm lucky.

 

 

 

 

Join the $150+ 400KM tank club mate. 





 


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  Reply # 2090016 13-Sep-2018 13:35
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The best fuel efficiency is to use what the manufacturer of the vehicle recommends.

 

Octane rating determines how much pressure the fuel will withstand before it ignites. If you are using fuel that is igniting late (Higher octane) or early (lower octane) then you will probably suffer timing issues.

 


I drive a BMW 335i and I don't really get much improvement from putting 98 octane fuel in in by comparison to 96 or 95. The car is rated for 95 or above. 

 

Personally I have found Caltex to be my go-to. The main reason being the stations are located in spots that convenience me, I save up my AA smartfuel discounts. And i'd rather pay the price of a 96 fuel over a 98 because its marginally cheaper.

 

BP has been ok too but most premium fuel is 98 so i end up paying slightly more for the same amount of gas.

 

I have had engine warning lights from Z before, but i think it was back when they had that bad batch of fuel, I have not really used them much since. And the other reason i don't go to mobil much is because its mainly synergy 8000 at my local mobils and costs a little more. 

 

Have had problems with gull before as well.

 

 






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  Reply # 2090021 13-Sep-2018 13:43
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Fuel igniting late then the timing is out not cause the octane of the fuel is to high for the car

Knocking is the fuel igniting before piston reaches TDC (top dead centre) and engine trying to run backwards

John




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  Reply # 2090028 13-Sep-2018 13:51
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Linux: Fuel igniting late then the timing is out not cause the octane of the fuel is to high for the car

Knocking is the fuel igniting before piston reaches TDC (top dead centre) and engine trying to run backwards

John

 

Yeh your right having a higher octane fuel wont matter, but it doesn't really give you any/much benefit over the rated fuel for the engine.






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  Reply # 2090077 13-Sep-2018 14:14
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darylblake:

 

Linux: Fuel igniting late then the timing is out not cause the octane of the fuel is to high for the car

Knocking is the fuel igniting before piston reaches TDC (top dead centre) and engine trying to run backwards

John

 

Yeh your right having a higher octane fuel wont matter, but it doesn't really give you any/much benefit over the rated fuel for the engine.

 

 

 

 

Not too sure if you can retard injectors to stop knocking.
I know you can adjust the duty cycle and that can help. But I think the ECU doesn't even have control over this in most vehicles.

 





 


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  Reply # 2090100 13-Sep-2018 14:32
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Would love to hear opinions on this as I don't know how true it is:

 

I read somewhere the best way to clean the fuel internals out is to run a couple of tanks of E10 as the ethanol will clean everything out but has a consequence of lifting the lacquer formed over time in fuel tanks which could block the fuel filter. Based on that I've always kept away from it.

 

There is a Youtube channel called "Chris Fix" where he has tested different fuel cleaners by doing before/afters with a borehole camera looking at the piston head, the only one I think he said that had a notable difference was Techron (same stuff Caltex uses)  


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  Reply # 2090103 13-Sep-2018 14:35
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The best way and only way is to get a professional to do the job and actually remove the injections

John




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  Reply # 2090105 13-Sep-2018 14:36
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No idea but at the start of each summer I pour a bottle of meths into my boat tank as my mechanic told me it helps absorb water condensation that's in the fuel.


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  Reply # 2090113 13-Sep-2018 14:44
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kryptonjohn:

No idea but at the start of each summer I pour a bottle of meths into my boat tank as my mechanic told me it helps absorb water condensation that's in the fuel.



Kind of correct water sits in the bottom of a fuel tank and when it's mixed with the meths it can then go thru the fuel system same as fuel and burn off in the engine

John




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  Reply # 2090128 13-Sep-2018 15:07
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Linux:
kryptonjohn:

 

No idea but at the start of each summer I pour a bottle of meths into my boat tank as my mechanic told me it helps absorb water condensation that's in the fuel.

 



Kind of correct water sits in the bottom of a fuel tank and when it's mixed with the meths it can then go thru the fuel system same as fuel and burn off in the engine

John


Apparently BP 98 used to have a water content in it to raise octane and this would happen.





 


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  Reply # 2090133 13-Sep-2018 15:12
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Coil:

Linux:
kryptonjohn:


No idea but at the start of each summer I pour a bottle of meths into my boat tank as my mechanic told me it helps absorb water condensation that's in the fuel.




Kind of correct water sits in the bottom of a fuel tank and when it's mixed with the meths it can then go thru the fuel system same as fuel and burn off in the engine

John


Apparently BP 98 used to have a water content in it to raise octane and this would happen.



Water to raise octane lol

John




Ex JohnR VodafoneNZ 17 years 4 days

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