Discussion
The DME will adjust (dial back) timing to eliminate any detonation the lower octane fuel contributes to.
This is good new bad news.
Good news in that detonation unchecked can render an engine ruined in no time.
Bad news in that by dialing back timing the engine produces less torque and suffers from increased fuel consumption. Furthermore, exhaust gas temperature is increased and this subjects all items exposed to exhaust gases to higher operating temperatures. This includes valves, piston crown, combustion chambers, O2 sensors and converters.
Now many engines have covered a lot of miles running lower octane grades of gasoline than what is called for. My Boxster's engine for one: 275K miles and the last 195K miles mostly running 91 octane vs. 93 octane. Can't buy but 91 octane where I live (CA).
However, in spite of this diet of 91 octane gasoline, the engine is still quite healthy.
But were it available I'd use 93 octane in a heart beat.
A few times with my Turbo I have had a chance to fill the tank with 93 octane gasoline and the engine is transformed. Not oodles more power but the engine was noticeably more responsive to the throttle. I didn't check fuel mileage -- probably a good thing as I was really "testing" the engine's throttle response every chance I got if you know what I mean and I think you do -- but when driving conditions are identical fuel economy goes up with the higher octane gasoline being used. This arises from the ignition timing being advanced so the mixture starts burning earlier and this results in more force being applied to the piston at a point in its travel when it is most optimum.
If you can't buy the proper grade of octane at least avoid running any thing lower than you absolutely can. The owners manual gives the lower limit and you should not go below this. And buy from a busy station to ensure the freshest fuel.
This is good new bad news.
Good news in that detonation unchecked can render an engine ruined in no time.
Bad news in that by dialing back timing the engine produces less torque and suffers from increased fuel consumption. Furthermore, exhaust gas temperature is increased and this subjects all items exposed to exhaust gases to higher operating temperatures. This includes valves, piston crown, combustion chambers, O2 sensors and converters.
Now many engines have covered a lot of miles running lower octane grades of gasoline than what is called for. My Boxster's engine for one: 275K miles and the last 195K miles mostly running 91 octane vs. 93 octane. Can't buy but 91 octane where I live (CA).
However, in spite of this diet of 91 octane gasoline, the engine is still quite healthy.
But were it available I'd use 93 octane in a heart beat.
A few times with my Turbo I have had a chance to fill the tank with 93 octane gasoline and the engine is transformed. Not oodles more power but the engine was noticeably more responsive to the throttle. I didn't check fuel mileage -- probably a good thing as I was really "testing" the engine's throttle response every chance I got if you know what I mean and I think you do -- but when driving conditions are identical fuel economy goes up with the higher octane gasoline being used. This arises from the ignition timing being advanced so the mixture starts burning earlier and this results in more force being applied to the piston at a point in its travel when it is most optimum.
If you can't buy the proper grade of octane at least avoid running any thing lower than you absolutely can. The owners manual gives the lower limit and you should not go below this. And buy from a busy station to ensure the freshest fuel.
I have never understood the argument that there is no difference between the fuels.
If you cant, you have a numb bottom and/or right foot or cannot hear your engine.
I also think (although am not 100% certain) that I can feel the difference between Shell and BP and that Shell is a tiny bit better. I dont notice any difference in acceleration, but the engine sounds every so slighter smoother (to my ears) with Shell.
(It actually seems to make a difference in crappy cars that are prob not set up for 98 RON, but I am less sure of that. In Porsches, it is quite noticeable - as is the MPG bump of maybe 1.5).
If you cant, you have a numb bottom and/or right foot or cannot hear your engine.
I also think (although am not 100% certain) that I can feel the difference between Shell and BP and that Shell is a tiny bit better. I dont notice any difference in acceleration, but the engine sounds every so slighter smoother (to my ears) with Shell.
(It actually seems to make a difference in crappy cars that are prob not set up for 98 RON, but I am less sure of that. In Porsches, it is quite noticeable - as is the MPG bump of maybe 1.5).
Here in jersey, the best you get 97ron with the super unleaded.
Recently the main fuel farm decided to stop storing the super unleaded, leaving just 95ron available.
There was a bit of an outcry and one garage has decided to import their own super unleaded supply, so 97 is available again.
I did wonder about just using 95 as it is far cheaper, but thought the guidelines were there for a reason by Porsche.
When away in France I fill up with the wizz-bang Shell stuff, but to be honest I don't feel any great difference.
Recently the main fuel farm decided to stop storing the super unleaded, leaving just 95ron available.
There was a bit of an outcry and one garage has decided to import their own super unleaded supply, so 97 is available again.
I did wonder about just using 95 as it is far cheaper, but thought the guidelines were there for a reason by Porsche.
When away in France I fill up with the wizz-bang Shell stuff, but to be honest I don't feel any great difference.
ORD said:
I have never understood the argument that there is no difference between the fuels.
Absolutely this. There's an unmistakeable difference in how my DFI 3.8 engine runs on V-Power compared to BP Ultimate.Put a tank of the 97-RON in after using V-Power for a while and you firstly notice the engine and exhaust notes change. Next, there's a marked and very significant decrease in low-to-mid-range torque. (No jokes please about non-turbo engines having no torque to start with please!
). The least affected is the top of the rpm range (other than a slightly smoother, but also slightly less urgent, delivery).Much as I hate to disagree with an earlier post, it IS during every day running that the lower octane fuel makes the biggest difference as the reduction in performance is greatest at low-medium rpm. (I'm assuming here that every day running means typical suburban driving, rather than max attack).
Usually Shell Vpower for me, though the odd tank of inferior fuel does no real harm. Several times in the middle of Cornwall/Cumbria I've had no option but to splash at the village Arkwrights Garage, where I am generally just relieved to see a pump with 'unleaded' written on it! Definite performance & economy drop off.
Put it this way, I wouldn't buy a performance car off someone, if they stated during viewing that they don't believe in performance fuel and have just bunged in cheapest fuel from wherever is closest when running out!
Put it this way, I wouldn't buy a performance car off someone, if they stated during viewing that they don't believe in performance fuel and have just bunged in cheapest fuel from wherever is closest when running out!
AlexH997 said:
SO basically I need to be using Shell V Power for my 997 for optimal fuel consumption and performance
V-Power or (I'll possibly get shot to pieces for this) Tesco Momentum. AFAIK, it's the only other 99-RON (or indeed 'above 97-RON') fuel available in the UK. As it's cut-price in comparison to Shell, there's been a lot of discussion about whether it has the same quality of additive package, but I've never seen/read anything definitive either way.ORD said:
I have never understood the argument that there is no difference between the fuels.
If you cant, you have a numb bottom and/or right foot or cannot hear your engine.
I also think (although am not 100% certain) that I can feel the difference between Shell and BP and that Shell is a tiny bit better. I dont notice any difference in acceleration, but the engine sounds every so slighter smoother (to my ears) with Shell.
(It actually seems to make a difference in crappy cars that are prob not set up for 98 RON, but I am less sure of that. In Porsches, it is quite noticeable - as is the MPG bump of maybe 1.5).
Back in IIRC 2006 EVO mag did a fuel (petrol) test and found there were differences between various brands of fuels of the same octane grade. If you cant, you have a numb bottom and/or right foot or cannot hear your engine.
I also think (although am not 100% certain) that I can feel the difference between Shell and BP and that Shell is a tiny bit better. I dont notice any difference in acceleration, but the engine sounds every so slighter smoother (to my ears) with Shell.
(It actually seems to make a difference in crappy cars that are prob not set up for 98 RON, but I am less sure of that. In Porsches, it is quite noticeable - as is the MPG bump of maybe 1.5).
EVO also found that even for the same brand/octane grade of fuel not every tank of the stuff was the same. This was traced to staleness.
The guidelines from the test were to buy a name brand fuel -- discount fuel stations buy from various suppliers -- to get the best price -- and the quality can vary -- and buy from a busy station to ensure the fuel is fresh.
Over here in the USA I have found some really busy stations get deliveries up to 4 times a day. I'd not go out of my way to find that busy of a station but there should be plenty of stations around that get resupplied every other day or so. And a busy station is often one that has lower prices so to use the popular expression: Bonus!
AlexH997 said:
its crazy to Porsche have designed a car which needs to be run on 98 RON yet only one real fuel supplier on the market provides this (plus tesco momentum)
I used momentum before and the fuel economy sucked in comparison to bp ultimate.
A lot of the Mistubishi Evo cars were built to run on 102 octane, but the spec had to be adjusted for official UK versions.I used momentum before and the fuel economy sucked in comparison to bp ultimate.
Rockster said:
...and buy from a busy station to ensure the fuel is fresh.
Over here in the USA I have found some really busy stations get deliveries up to 4 times a day. I'd not go out of my way to find that busy of a station but there should be plenty of stations around that get resupplied every other day or so. And a busy station is often one that has lower prices so to use the popular expression: Bonus!
I think this is probably overkill - it's petrol we're discussing, not milk! I can't remember when I last filled my 996 (I haven't used it since its service in early November) and I don't expect the performance to be notably different when I do take it for a run. Likewise my Cayenne has been filled once since the previous tankful on October 6th.Over here in the USA I have found some really busy stations get deliveries up to 4 times a day. I'd not go out of my way to find that busy of a station but there should be plenty of stations around that get resupplied every other day or so. And a busy station is often one that has lower prices so to use the popular expression: Bonus!
The point is, yes fresh is good but a little perspective is needed, and there's every chance the car will be re-filled less often than the fuel station gets supplies anyway.
AlexH997 said:
its crazy to Porsche have designed a car which needs to be run on 98 RON yet only one real fuel supplier on the market provides this (plus tesco momentum)
I used momentum before and the fuel economy sucked in comparison to bp ultimate.
Not as crazy as it seems - 98-RON is the norm for premium unleaded across Europe. It's only here in the f**cked-up UK where we get second-rate petrol.I used momentum before and the fuel economy sucked in comparison to bp ultimate.
Others will know the detail of this better than me but there is a fair debate around the classic cars on another angle of the fuel going stale when cars are left standing for a while - aside from Porsche have a race engined jag XK120 if that isnt driven for a couple of months you notice that the modern fuel loses the octane rating pretty quickly apart from perishing rubber hoses etc
I now put tetraboost octane additive in to protect against this
I now put tetraboost octane additive in to protect against this
stevod said:
The only OPC that I've ever asked about fuel have a policy of only using standard unleaded in their demonstrators.
S
Yep. One of the many things that OPCs say that contradict (a) actual Porsche advice and (b) common sense. S
It says a lot that they feed the demos average fuel.
I frankly don't trust most OPCs at all. I wouldn't want Hatfield cleaning my car, tbh.
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