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

[zcacogp]

Chaps, 

I am sure this has been asked on here before and I am also sure that it is as contentious a question as the one about oil that comes up ALL THE TIME, but .... 

.... is ti worth forking out the extra on 98 octane fuel for a 987.1 non-S model? 

(I can see both sides of the argument and can definitely assure anyone that cares that paying the extra two bob a litre for 98 in a 944 S2 is worth the extra money as it is more than compensated for by extra MPG and the power and smoothness is a bonus, but that's a different car altogether. 😀 )

Thanks!

[Bike Loon]

Yes it does come up all the time, if you had used the search function you would have found plenty of existing threads on it

[red rocket]

Yep, there was a very recent thread! Fwiw I tend to use higher Octane; either Shell V Power if i'm in the vicinity of a Shell garage or Tesco Momentum. But I only do around 5k a year; might be different if i was topping up every week.

[zcacogp]

Yeah, but I'm an idle hound. 

Anyone care to post some links to some of those recent threads? Please don't make me use the search function. Please ..... 

[red rocket]

7 minutes ago, zcacogp said:

Yeah, but I'm an idle hound. 

Anyone care to post some links to some of those recent threads? Please don't make me use the search function. Please ..... 

Shell V Power petrol

 

[zcacogp]

Fanks RR! 🥰

[Ninesomething]

I always use momentum because Tesco is pretty handy. I don't do many miles. 2.7 so it needs all the help it can get.....

[Paul P]

My take. 
 

higher Ron. Bit better mpg, that’s what Porsche say to use. if I can. I will. If I can’t, don’t give it a second thought. It feels “nicer” to me. 
 

but

better detergents, low or zero ethanol content so “branded” fuel vs supermarket chip fat - i will go for that.  
 

So me, for my car, for my use, higher ron, esso or shell is the default over time (and usually esso beciase PCGB fuel card gives you 2p a litre off esso super whatever it’s called ) and my two nearest stations are esso  

it’s currently sipping its way through BP super and it seems happy  

But on a rainy night 300 miles from home I will take what I can get and the car will deal with it and neither me nor it will likely notice. 

Your car, your cash, your rules.  

[Menoporsche]

…your search keywords…

[½cwt]

@Paul P  Sipping??? You should be trying harder!

[Greenman]

99 Octane is the only one worth bothering with.   Porsche is lumpy and slow on 95 and can barely keep up with a Hyundai i10 https://www.autoexpress.co.uk/best-cars-vans/355117/slowest-cars-sale-now

…

…

 

on the other hand any difference may be marginal, take your pick.

[DaveEFI]

In better times, I visit my home town and some family about 500 miles away regularly. And it's a bit or a ritual. Use 98 one way and 95 the other, and log the MPG. And I've never had a conclusive result.😉 Porsche say to use 98. When means the base timing will be retarded for 95. Inevitably resulting in poorer MPG. So very odd I'm not seeing that.

[EXY]

11 minutes ago, DaveEFI said:

In better times, I visit my home town and some family about 500 miles away regularly. And it's a bit or a ritual. Use 98 one way and 95 the other, and log the MPG. And I've never had a conclusive result.😉 Porsche say to use 98. When means the base timing will be retarded for 95. Inevitably resulting in poorer MPG. So very odd I'm not seeing that.

I've read that it can take a tankfull(or three) to get the full benefits 

[Scubaregs]

Did this a few years ago on my work commute in a GT86.

One month regular, one month premium.

MPG gain pretty much paid the difference in price for the premium.

[dpg123]

When I bought our Macan last week, the Porsche Dealer said "it says super unleaded on the fuel filler, but in the UK it makes no difference - just use normal unleaded".

[DaveEFI]

21 hours ago, EXY said:

I've read that it can take a tankfull(or three) to get the full benefits 

I've read that too - and it makes no sense. The engine has knock sensors which keep the timing below knock point. Why would is take several tanks of high octane to get the timing back to normal? Since Porsche imply high octane is the norm?

[DaveEFI]

20 hours ago, Scubaregs said:

Did this a few years ago on my work commute in a GT86.

One month regular, one month premium.

MPG gain pretty much paid the difference in price for the premium.

In general, I fill up. And zero the MPG, average speed and trip counter. Run until the warning light comes on. And repeat. And have tried alternate tanks of 95 and 98. No consistent difference.

[½cwt]

7 hours ago, DaveEFI said:

I've read that too - and it makes no sense. The engine has knock sensors which keep the timing below knock point. Why would is take several tanks of high octane to get the timing back to normal? Since Porsche imply high octane is the norm?

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.

[EXY]

9 hours ago, DaveEFI said:

I've read that too - and it makes no sense. The engine has knock sensors which keep the timing below knock point. Why would is take several tanks of high octane to get the timing back to normal? Since Porsche imply high octane is the norm?

I think it's still petrol related,,,,

They can and do put the price up in a heartbeat BUT there is always a LOT of hand wringing and prevarication before they will even consider lowering it

IIRC it has something to do with retardation is fairly safe but advancing can be dangerous. 

[½cwt]

56 minutes ago, EXY said:

I think it's still petrol related,,,,

They can and do put the price up in a heartbeat BUT there is always a LOT of hand wringing and prevarication before they will even consider lowering it

IIRC it has something to do with retardation is fairly safe but advancing can be dangerous. 

Retarding the spark is the safe direction but it also reduces power as the explosion starts later in the power stroke of the engine.

[Megatonks]

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

 

 

[EXY]

11 hours ago, ½cwt said:

Retarding the spark is the safe direction.

Isn't that what I said 🤔

95 requires greater ignition retardation than 98 hence reduced power which also equates to reduced efficiency so providing everything else is equal i.e. you don't use the increased power you will get improved MPG.

So most want the best from their Por-scha so why not use the fuel with the capability of allowing the vehicle to produce power as per the manufacturers specification, have we mentioned N Rated tyres yet.

Remember the higher the RON simply means the fuel has a greater ability to resist a premature flame front and my comment was 'it has something to do with retardation is fairly safe but advancing can be dangerous.'

So IIRC you have to be careful advancing and introducing knock which can be detrimental to engine longevity. Hence you can retard it without penalty to engine longevity (safe) but advancing can introduce knock (dangerous).

This might be why it takes a few tankfuls to get up to the same levels of advance, for safety as an engine suffering predetonation (knock) can destroy itself quickety-quick.

 

[DaveEFI]

15 hours ago, 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.

For a knock sensor to make any sense it must react near instantly to a low octane petrol. So can't for the life of me see why it should take several tanks to reverse that.

[½cwt]

19 minutes ago, EXY said:

Isn't that what I said 🤔

 

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

Ho hum.

[½cwt]

Just now, ½cwt said:

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

Ho hum.

Depends how 'safe' the ECU is once it detects a knock. Some do not try to advance again once knocked back.  Not sure how the Porsche DME unit works, but it may test the knock limit to re advance over a period of time rather than assuming it can immediately go to a higher advance setting once it has retarded to keep the engine safe.