93 vs 91 octane
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I'm in NorCal, the 91 Supreme at Chevron (and everywhere else) is just fine and I drive a lot at full throttle. On my previous 987 Boxster S of 12 years, for economy I often alternated with the cheaper middle-grade Plus (89?) and never encountered knocking. Same with our other German cars which recommend 93.
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The manual does say that the slightly reduced octane stuff is OK, the engine management unit adjusts the performance down to cope.
Here in Australia we use the straight RON index and 96 is recommended. I can get 98 everywhere and 100 in places. I haven't used the 95--our standard 'super'--so I can't comment on how far down the performance drops.
There are some decent octane boosters around, a bit of Google searching should give you guide to what works best (I know some make almost NO difference). I'd be giving it a try and seeing if I could tell the difference and whether it's worth the extra cost.
Here in Australia we use the straight RON index and 96 is recommended. I can get 98 everywhere and 100 in places. I haven't used the 95--our standard 'super'--so I can't comment on how far down the performance drops.
There are some decent octane boosters around, a bit of Google searching should give you guide to what works best (I know some make almost NO difference). I'd be giving it a try and seeing if I could tell the difference and whether it's worth the extra cost.
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I'm confused. Here in UK, we have 95 which is the standard stuff and 97 or 98 (depending on brand) which is top end. Words like premium and super mean nothing as different brands use different names. In parts Europe you can occasionally find 100 octane but not UK. I just wonder if your 91 is our 95 and your 93 is our 98. After all your gallon is only 4 fifths of ours with 16 fluid ozs rather than 20 to the pint! Half the price per gallon for 4 fifths the quantity can't be bad though!
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The UK and Australia (at least) use the straight RON method for rating octane. The USA (and others) use (RON+MON)/2.
There is not a direct relation between RON and MON. (Wikipedia has details.)
I assume the different countries have different manuals and different stickers inside the fuel inlet cover.
There is not a direct relation between RON and MON. (Wikipedia has details.)
I assume the different countries have different manuals and different stickers inside the fuel inlet cover.
Cheap Thrills.
Where I live you can pump Chevron 94 octane gas for about $2-$3 more per tank than the 91 grade. And, it is certified to not contain any alcohol. Yes, that's rated using the NA (R+M)/2 octane standard. I started using it when I installed a Dinan ECU mod on my BMW 2 series and have continued using it in my Boxster S. Honestly cannot notice much, if any, difference from Chevron's 91.
Where I live you can pump Chevron 94 octane gas for about $2-$3 more per tank than the 91 grade. And, it is certified to not contain any alcohol. Yes, that's rated using the NA (R+M)/2 octane standard. I started using it when I installed a Dinan ECU mod on my BMW 2 series and have continued using it in my Boxster S. Honestly cannot notice much, if any, difference from Chevron's 91.
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:laugh: 0
While I emphasised the performance reduction that the ECU makes to cope with "under octane" fuel I sincerely doubt that most drivers would notice any difference. The outstanding performance of the 718 would mean that the difference is probably less than ⅛" of throttle travel.
I doubt if I could notice that.
While I emphasised the performance reduction that the ECU makes to cope with "under octane" fuel I sincerely doubt that most drivers would notice any difference. The outstanding performance of the 718 would mean that the difference is probably less than ⅛" of throttle travel.
I doubt if I could notice that.
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Ah, that explains it. Thanks. I don't discern any difference between 95 and 98 but it is apparently better for your engine wear and tear. I did notice a huge difference with 100 RON in Germany. Like aviation fuel on performance and sound, throttle blips in standard mode. But I reckon the mpg wasn't very good - unless that was because I was encouraged to more spirited driving.
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There's a place in Sunol that has race gas, but otherwise yeah it's 91 here in Cali. I have to assume that's ok. On my nice cars I've ONLY put Chevron in for the longest time because I heard at some point that Techron actually works well, and was a competitive advantage over other companies, but that could be all BS these days.
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Maybe yes
and maybe no. There have been tests of fuel here that show some fuels are actually under rated and others over rated.Automotive journalists tell us that the lower octane number than recommended is bad. However, they have also repeated over the years that putting the octane number higher than recommended is a waste of money because it does not increase the performance or the longevity of the engine.
Can anyone confirm that?
Can anyone confirm that?
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Octane is a measure of how much compression the fuel can take before it detonates.
Lower octane than 'useable' used to cause detonation or "pinging" which was bad. That means the fuel ignited irregularly rather than burning predictably, timing was changed, and cylinder pressures could skyrocket.
With the advent of highly computerised engine management units a slightly lower octane is usually no issue as the computer can "de-tune" the engine slightly to compensate.
All other things (fuel composition, additives, etc.) being equal, an octane rating higher than needed would not change engine performance, and is a waste of money. Of course very high octane car fuels often have alcohols or octane boosters added which change the composition. They may also clean out cylinder/piston deposits and that can change performance.
With leaded fuels the engine performance could be confirmed by the colour of the carbon deposits in the tail pipe. Unleaded and computers mean that this is no longer useful.
Avgas at 100 octane+ or racing gas should not be used in engines designed for unleaded fuels as they contain lead to increase the octane rating and significant damage can occur with significant use.
Lower octane than 'useable' used to cause detonation or "pinging" which was bad. That means the fuel ignited irregularly rather than burning predictably, timing was changed, and cylinder pressures could skyrocket.
With the advent of highly computerised engine management units a slightly lower octane is usually no issue as the computer can "de-tune" the engine slightly to compensate.
All other things (fuel composition, additives, etc.) being equal, an octane rating higher than needed would not change engine performance, and is a waste of money. Of course very high octane car fuels often have alcohols or octane boosters added which change the composition. They may also clean out cylinder/piston deposits and that can change performance.
With leaded fuels the engine performance could be confirmed by the colour of the carbon deposits in the tail pipe. Unleaded and computers mean that this is no longer useful.
Avgas at 100 octane+ or racing gas should not be used in engines designed for unleaded fuels as they contain lead to increase the octane rating and significant damage can occur with significant use.
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So are you saying with certainty that the 100 octane Shell 'Racing' is actually a leaded fuel or at least partially leaded and, thus, will damage the cat converter and/or other engine parts? If so, this is good to know, thanks. It definitely made my 981 basic boxster go like an S and throttle blip even without being in sport mode. But with poor mpg consumption. Haven't tried it in the 718S and now definitely won't!
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I can't guarantee the lead content in any particular racing fuel but lead is in most as an octane booster. I sure wouldn't be using it without checking with the distributor/manufacturer.
Poor consumption indicates that there may be methanol there and that the fuel/air mixture has changed. It is quite usual for race engines to be tuned differently than street engines.
Maybe there is a UK fuel specialist here that can give exact specifications.
Poor consumption indicates that there may be methanol there and that the fuel/air mixture has changed. It is quite usual for race engines to be tuned differently than street engines.
Maybe there is a UK fuel specialist here that can give exact specifications.
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I adhere to the Top Tier list when fueling my vehicles:
https://www.toptiergas.com/licensedbrands/
There are many discussions about fuel quality in other forums, and generally the list above is what comes up as the most reliable way to keep giving your car quality fuel, at least in the U.S.
Of note, however, is that Top Tier started a rather heavy marketing push to align itself closer to the petroleum industry, as opposed to the vehicle industry, more than two years ago. (Background: Top Tier was started by several carmakers about 15 years ago and is still partially funded by them, including GM, BMW, Mercedes-Benz, and VW AG.) The skeptic in me is wary of this shift. I've not heard of any drastic changes in its standards because of this, so I continue to put only Top Tier fuel in my car.
https://www.toptiergas.com/licensedbrands/
There are many discussions about fuel quality in other forums, and generally the list above is what comes up as the most reliable way to keep giving your car quality fuel, at least in the U.S.
Of note, however, is that Top Tier started a rather heavy marketing push to align itself closer to the petroleum industry, as opposed to the vehicle industry, more than two years ago. (Background: Top Tier was started by several carmakers about 15 years ago and is still partially funded by them, including GM, BMW, Mercedes-Benz, and VW AG.) The skeptic in me is wary of this shift. I've not heard of any drastic changes in its standards because of this, so I continue to put only Top Tier fuel in my car.
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