95 or 98 Octane .... ? (Runs for cover)

[EXY]

2 minutes ago, ½cwt said:

Sort of, it didn't read as though you were fully committed to it, so I was confirming.

Ho hum.

I hear you Chris.

When I'm on my mobile my replies are often curtailed, no doubt to the benefit of the forum for the most part 😅

[Required]

4 hours ago, Megatonks said:

I thought the only options over BP's 97 Ultimate was Shell Vpower 99 or Tesco's Momentum.

 

There's apparently a new 99 choice for anyone with an Esso nearby

https://www.esso.co.uk/en-gb/fuels/petrol

 

 

Tesco Momentum is a mythical fuel as far as I'm concerned.  No Tesco I visit seems to offer it.  And Shell stations seem to be vanishing from the motorways.  Returning from Wales a few weeks ago I kept driving in to services where the sign on the motorway said Shell, to find some weird own-brand, and no high octane.  Eventually found it at an Esso station.

[david_yorkshire]

Move to Watford; 3 x Shell garages within 5 miles of each other & Tesco sell their rocket fuel locally - not that I've tried it...

GT3 has had exclusively Shell V Power over the past 8 years

Scoob runs Shell V power exclusively

X5 runs 50:50 Shell norm diesel & Sainsbury's bog diesel

 

[Menoporsche]

2 hours ago, david_yorkshire said:

Move to Watford

Ha! Finally a reason!  

[the baron]

We’re all going to be using 97 shortly anyway according to the government, so that decision will be taken away from you, so for those of us that use 95 me included fill your boots while you can

[McDonald]

39 minutes ago, the baron said:

We’re all going to be using 97 shortly anyway according to the government, so that decision will be taken away from you, so for those of us that use 95 me included fill your boots while you can

Keeping petrol in the boot is very dangerous. Don't try this at home, folks.

[DaveEFI]

On 8/4/2021 at 6:21 PM, ½cwt said:

Depends how long it takes the DME to unlearn the leads advanced timing that it will have set to with the 95 octane fuel. Does it test the knock limit all the time? Some other marques I know once retarded for lower octane file you have to do something to reset like disconnect the ECU for 30 mins to allow it to reset and relearn the knock limits once you use higher octane file again. Besides the higher octane will give a bit bigger bang but the knock resistance and so the advance it allows also adds to the power of each combustion.

It has to 'look' for knocking all the time. As detonation can wreck the engine. If it doesn't, you might as well just set the timing for the poorest fuel around. And have to adjust it for better.

[½cwt]

53 minutes ago, DaveEFI said:

It has to 'look' for knocking all the time. As detonation can wreck the engine. If it doesn't, you might as well just set the timing for the poorest fuel around. And have to adjust it for better.

But can anyone confirm it looks forward for knock again once it has been retarded? @Richard Hamilton ? The classic Impreza Turbo did not once it had retarded for example. You disconnected the ECU for 30 mins, or overnight to be certain, to cancel the learning forcing it to then re learn.

[Richard Hamilton]

I can't say for sure, but it would surprise me if the adaptation process was a one way street.

On electronic throttle 986s you don't have to disconnect the battery to reset it.  Just switch the ignotion on for 60 seconds, but don't touch the throttle pedal.  Then switch it off for at least 10 seconds, and it will reset it to factory settings.

[½cwt]

3 hours ago, Richard Hamilton said:

I can't say for sure, but it would surprise me if the adaptation process was a one way street.

On electronic throttle 986s you don't have to disconnect the battery to reset it.  Just switch the ignotion on for 60 seconds, but don't touch the throttle pedal.  Then switch it off for at least 10 seconds, and it will reset it to factory settings.

Thanks Richard. I guess it is just a case of how quickly or how far it gets to find the optimum again once fed with the good stuff after a dose is 95. As I noted the classic Impreza did not get all the way back and it's electronics origins are only about 3 years older than the Boxster.

[DaveEFI]

15 hours ago, Richard Hamilton said:

I can't say for sure, but it would surprise me if the adaptation process was a one way street.

On electronic throttle 986s you don't have to disconnect the battery to reset it.  Just switch the ignotion on for 60 seconds, but don't touch the throttle pedal.  Then switch it off for at least 10 seconds, and it will reset it to factory settings.

This is my thinking too. Makes no sense to have a sensor that only reacts in one direction. I have fitted a MegaSquirt to my other car, and know how the (added) knock sensors on that reacts. I can see a learning ECU - like say the one that controls an auto, and adapts to how you normally drive, taking time to update its settings. But one which effects both MPG and emissions - let alone performance - should react as quickly as possible.

 

I'd love to see some accurate data, taken on a rolling road etc where the circumstances are under control, for the extra power and MPG when using 97 octane versus 95. Rather than the usual apocryphal stuff.

[moneypit]

In my experience, it takes a tankful to see a difference. Usually more critical on a modified turbocharged car with regards to longevity, I doubt using a lower octane fuel on an NA car matters as much. Bizarrely, out of all the stuff I own, our Lexus IS300 responds best to high octane fuel, much more responsive. Esso are doing a 99 octane, reputedly the best on the market. My Evo likes it........

[plynchy]

Did read somewhere that Esso doesn't have the Ethanol content of the others, which some folk find appealing.

As for source of fuel, it's all stored in the same huge tanks. Next time you drive South over the Dartford crossing take a look to your left, those tanks are where the bulk of the SE fuel comes from. It has different additives added at point of loading depending on the brand.

FWIW i've always used super of some description in every high powered car i've owned, seems daft not to when the manufacturer writes it on the fuel cap.

[zcacogp]

On 8/6/2021 at 9:43 PM, ½cwt said:

Thanks Richard. I guess it is just a case of how quickly or how far it gets to find the optimum again once fed with the good stuff after a dose is 95. As I noted the classic Impreza did not get all the way back and it's electronics origins are only about 3 years older than the Boxster.

Interesting info there about the Impreza, although that sounds very primitive to me. Advancing ignition to the point of knock then backing off again is something that has been done by cars equipped with knock sensors (effectively small microphones strapped to the side of the block) for yonks, the usual question is how frequently the ECU makes adjustments - 10's of times a second or 100's of times a second. 

My old 944 does better on the high octane stuff and you can tell the difference when going from low to high octane by the time you're off the petrol station forecourt. I'd be amazed if the 987 models weren't substantially quicker still. 

[½cwt]

Bottom line is you get a bigger bang at a more efficient place in the cycle of the engine.  As to cost effectiveness and all that, that is an individual choice, but as @plynchy says if it is what Porsche recommends, even if the manual says you can use 95 if necessary.  Why live on only 2000 calories a day when ideally you should be on 2500 (as an adult male) for a heathy diet?

[Menoporsche]

On 8/7/2021 at 10:46 AM, DaveEFI said:

love to see some accurate data, taken on a rolling road etc where the circumstances are under control, for the extra power and MPG when using 97 octane versus 95. Rather than the usual apocryphal stuff.

Facts kill all the fun out of internet discussion. 

[McDonald]

2 minutes ago, Menoporsche said:

Facts kill all the fun out of internet discussion. 

This recalls pre-covid days when the title "expert" became an expletive. It was immensely popular for a while but happily no more.

[ATM]

Only use Tesco 99 in all my cars and have done for years

 

[DaveEFI]

2 hours ago, ½cwt said:

Bottom line is you get a bigger bang at a more efficient place in the cycle of the engine.  As to cost effectiveness and all that, that is an individual choice, but as @plynchy says if it is what Porsche recommends, even if the manual says you can use 95 if necessary.  Why live on only 2000 calories a day when ideally you should be on 2500 (as an adult male) for a heathy diet?

If you maintain your body weight on 2000 calories, change to 2500 and you'll get fat.😁

[Stuart21UK]

42 minutes ago, DaveEFI said:

If you maintain your body weight on 2000 calories, change to 2500 and you'll get fat.😁

and reliant on the calories going forward....at least psychologically 😉

Edited August 8, 2021 by Stuart21UK

[½cwt]

41 minutes ago, Stuart21UK said:

and reliant on the calories going forward....at least psychologically 😉

But why buy a sports car and then restrict it's performance?  We are talking elite athletes here, now middle aged spread.  Give 'em the fuel they were designed to have and also need to get the best out of them.

[EXY]

OK now where did we land on N Rated tyres?

[Scubaregs]

6 minutes ago, EXY said:

OK now where did we land on N Rated tyres?

[Stuart21UK]

2 hours ago, ½cwt said:

But why buy a sports car and then restrict it's performance?  We are talking elite athletes here, now middle aged spread.  Give 'em the fuel they were designed to have and also need to get the best out of them.

Mine does 172mph top speed, doesn't mean I drive it at that speed though so you could also ask

'Why buy a car that does 172mph, and not do it?'

Anyway the proper answer is why does it need 97ron when it runs fine on 95ron?

As a daily driver (more in the 1st 6yrs than now) why spend 10-30p per litre more than I need to when my own measurements proved very marginal mpg improvements?

If you have a garage queen, and do a low mileage then you go ahead and pamper it....for me it unnecessary, so I dont feel the need to  

[McDonald]

10 minutes ago, Stuart21UK said:

Mine does 172mph top speed, doesn't mean I drive it at that speed though so you could also ask

'Why buy a car that does 172mph, and not do it?'

Anyway the proper answer is why does it need 97ron when it runs fine on 95ron?

As a daily driver (more in the 1st 6yrs than now) why spend 10-30p per litre more than I need to when my own measurements proved very marginal mpg improvements?

If you have a garage queen, and do a low mileage then you go ahead and pamper it....for me it unnecessary, so I dont feel the need to  

Smoother running & longer engine life?

Porsche recommend it, perhaps for a reason.

You probably buy top quality tyres, you could run on-ditch finders to save a few quid.

It's a mindset.