Premium over Regular Unleaded?

I don't think there is any noticeable difference in performance and I don't even think there is much economy difference. Much more economy difference in whether I have been for a hoon or not! :driving:

I have however bought into the extra additive spiel and always use BP Ultimate (easiest premium near me) but don't worry overmuch if on a trip and no premium available although will try to get some. Makes me feel better to put the best in. :thumbsup:
 
I have three other vehicles all oil burners, when I go in to fill the Z up I must look a right numpty I check, check and check again that I have the green nozzle in my hand.
 
I think that the diesel nozzles are a larger diameter to unleaded so they wont fit and you cant fill up with diesel.
 
As I understand it if you put better (higher octane) fuel in your car it will go better. The Z4 has a knock sensor. Poor quality fuel and the ignition timing will be retarded to prevent pinking (knock). Higher octane fuels allows the timing to be more advanced.

That's how I understand it.
 
I tend to use 95 ron and add redex every couple of tanks. Makes a world of difference to drivability.
 
I always use Shell V Power in my 3.4 as Alpina advise to only use premium for this engine so never tried any of the cheaper varieties.

When I had my '95 Merc SL500 I noticed a definite increase in fuel economy when I switched to premium fuel. Some of the US cars I saw had a "premium fuel only" sticker on the instrument cluster.
 
G-A-R-Y said:
As I understand it if you put better (higher octane) fuel in your car it will go better. The Z4 has a knock sensor. Poor quality fuel and the ignition timing will be retarded to prevent pinking (knock). Higher octane fuels allows the timing to be more advanced.

That's how I understand it.
Click to expand...

This reminds me of a similar conversation a couple of months ago. The principles you explain are broadly what happens, as lower octane fuel ignites sooner/more easily than high octane fuel and that will affect timing. But. IIRC this is only an issue on high compression engines, and only the M has a high compression engine in the range. If you put lower octane fuel in an M it will ignite sooner than the ECU requires, throw the timing out and have a negative impact on performance.

For the range as a whole I think the pluses of high octane are all about economy and any cleaning benefits you get from the additives. I ran my 3.0Si on 95 for two and a half years and it performed fine.
 
Rorybeanbutler said:
I tend to use 95 ron and add redex every couple of tanks. Makes a world of difference to drivability.
Click to expand...
I've only heard good things about BG44K, the rest seem a bit hit and miss as far as reviews go.
 
Bing said:
....But. IIRC this is only an issue on high compression engines, and only the M has a high compression engine in the range.
Click to expand...

I know that the ///M at 11.5:1 is the highest in the range (Alpinas are at 10.2:1), but the 2.5 engines are at 11:1. However, Alpina recommend 98+ RON for it's ratio of 10.2:1, and as there is a direct correlation between using higher RON grades for higher compression ratios (although engine temperature also comes into the mix), it seems to imply that all of the Z4 range are considered as high compression ratio engines?

As an aside, I've seen "very high compression ratio" defined as 14 and above, and "high compression ratio" defined as 10 and above... but never seen an "official" grading of compression ratios.

As an additional discussion point, I have a chart aligning RON and compression ratios. There is a US FAQ that I've used in the past as a source, and converted the US OR (Octane Rating) to RON using a OR=(22/21)*RON.

It shows:

Code: 
compression ratio          octane rating                   RON
		
           5:1	                     72                    69
           6:1	                     81                    77
           7:1	                     87                    83
           8:1	                     92                    88
           9:1	                     96                    92
          10:1                        100                   95
          11:1                        104                   99
          12:1                        108                  103


link if anyones interested in the specs
link if anyone's interested in the US FAQ sheet on gasoline ratings
 
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