colin smith
PCGB Member
Quick question should I be using 95 or 98 octane unleaded in my 86 model year car. There seems to be some confusion.
Thanks
Colin
Thanks
Colin
Fuel
- Thread starter colin smith
- Start date
Guest
New member
[
]Colin,
I have a ' 86 also, and if you look on the fuel filler lid you' ll see " 98 Ron" stamped on the inside. Like others I know I tend to use Helix from Shell (ouch[]), and then every alternate refill I use 95 octane. I can average around 28 to 29 mpg doing this, with Motorway driving, averaging 80mph. I know when tappets need adjusting as this figure drops to 24 mpg.
Some guys on Pelican have warned that regular use of 95 will lead to damaged valves.
Shine on,
Peter
]Colin,I have a ' 86 also, and if you look on the fuel filler lid you' ll see " 98 Ron" stamped on the inside. Like others I know I tend to use Helix from Shell (ouch[
]), and then every alternate refill I use 95 octane. I can average around 28 to 29 mpg doing this, with Motorway driving, averaging 80mph. I know when tappets need adjusting as this figure drops to 24 mpg. Some guys on Pelican have warned that regular use of 95 will lead to damaged valves.
Shine on,
Peter
colin smith
PCGB Member
OK I' ll stick to opitmax then, even though I don' t like Mike Schumacher !!!!!
ClubSport 911
New member
Optimax much better, but regarding the Octane and DME settings, inside you' ll find an 8 point adjuster for timing and injector duration - the DME is only " self adjusting" at the onset of pre-ignition / detonation - almost never going to occur on low compression, mild engine tune of the 3.2 as standard.
I' ll dig out the DME settings from my Database and post them here ASAP - I have had many reports of improved driving when upgrading to 98 octane and then re-adjusting the settings of the DME to compensate. Steve
I' ll dig out the DME settings from my Database and post them here ASAP - I have had many reports of improved driving when upgrading to 98 octane and then re-adjusting the settings of the DME to compensate. Steve
Guest
New member
On the subject of fuel, here is a quote off Autofarm' s website:
Q. Can I run my car on Unleaded Fuel?
A. In our opinion, yes (and it is only our opinion not necessarily that of Officialdom). The excellent quality of material used in Porsche valves and valve seats means that lead is unnecessary, so the question remaining is one of octane. In our experience (backed up by official statements and customer experience) nearly all models will run quite happily on "Ëśordinary' unleaded, 95 octane, BUT if "Ëśpinking' is heard, move up to "Ëśsuper' unleaded, 98 octane. Aren't you glad you found our website? Think how much this visit has just saved you..... perhaps we can now tempt you to buy something else from our mail-order parts department...!!
No affiliation with Autofarm, but I think that most acknowledge that they know what they are talking about.
Richard
Q. Can I run my car on Unleaded Fuel?
A. In our opinion, yes (and it is only our opinion not necessarily that of Officialdom). The excellent quality of material used in Porsche valves and valve seats means that lead is unnecessary, so the question remaining is one of octane. In our experience (backed up by official statements and customer experience) nearly all models will run quite happily on "Ëśordinary' unleaded, 95 octane, BUT if "Ëśpinking' is heard, move up to "Ëśsuper' unleaded, 98 octane. Aren't you glad you found our website? Think how much this visit has just saved you..... perhaps we can now tempt you to buy something else from our mail-order parts department...!!
No affiliation with Autofarm, but I think that most acknowledge that they know what they are talking about.
Richard
ClubSport 911
New member
Here are some notes I picked up about the DME settings on the 911 Carerra. No guarantees, but if your idle is a little rough and / or you can stick to super undleaded you might find these settings help
Basically the switch keeps the timing the same and adjusts the fuel, or retards the timing -3 degrees and adjust the fuel for not so good petrol (lower octane)
Postion 1 is fully counter clockwise:
Fuel / Ignition
1 0 0 stock setting
2 +3% 0
3 +6% 0
4 -3% 0
5 0 -3deg
6 +3% -3deg
7 +6% -3deg
8 -3% -3deg
Have fun playing !
Basically the switch keeps the timing the same and adjusts the fuel, or retards the timing -3 degrees and adjust the fuel for not so good petrol (lower octane)
Postion 1 is fully counter clockwise:
Fuel / Ignition
1 0 0 stock setting
2 +3% 0
3 +6% 0
4 -3% 0
5 0 -3deg
6 +3% -3deg
7 +6% -3deg
8 -3% -3deg
Have fun playing !
Simon Davidson
New member
I read recently that 98 super unleaded type fuels actually degrade when left in the tank and quickly get back to around 95 octane. anyone have any thoughts?
My car now runs on full unleaded for the first time in 16 years, cant say i can feel a difference between LRP, 95 or 98 so will get whats cheapest.
has anyone ever used octane boosters, nearly bought a bottle once but I couldnt find my basecall cap to wear back to front while swaggering down to the tills at Halfords.
Cheers Si
PS dont forget this saturday at JZ Machtech
My car now runs on full unleaded for the first time in 16 years, cant say i can feel a difference between LRP, 95 or 98 so will get whats cheapest.
has anyone ever used octane boosters, nearly bought a bottle once but I couldnt find my basecall cap to wear back to front while swaggering down to the tills at Halfords.
Cheers Si
PS dont forget this saturday at JZ Machtech
Diver944
Active member
I have also read that Super Unleaded will gradually fade over time, this was on an Internet bulletin board though so cannot vouch for it' s accuracy.
The same board also mentioned to read the small print of octane boosters. Most state they raise the octane by two points so you would think that 98 now goes to 100 []
In fact it is points of an octane, so 98 now becomes 98.2 []
Have we got any petrochemists out there?
The same board also mentioned to read the small print of octane boosters. Most state they raise the octane by two points so you would think that 98 now goes to 100 [
]In fact it is points of an octane, so 98 now becomes 98.2 [
]Have we got any petrochemists out there?
There is some interesting information here http://www.elektro.com/~audi/audi/toluene.html
on octane booster - especially when you compare the price of toluene to Unleaded - though if you were using it as a fuel you should pay fuel tax on it which would make it more expensive.
Tony
on octane booster - especially when you compare the price of toluene to Unleaded - though if you were using it as a fuel you should pay fuel tax on it which would make it more expensive.
Tony
Guest
New member
My understanding is that the Octane rating has nothing to do with power output.
It is a measure of the fuels knock resistance, that is, its ability to resist pre-ignition. You want the fuel/air mixture to ignite when you apply the spark, so that you have control over the timing and the flame front (since you know when and where in the cylinder the burn will start).
The ignition may occur due to the heat created by the compression, as in a diesel engine, if the octane rating is too low. The higher the compression ratio, the more heat is generated by compression and the higher the likelihood of pre-ignition.
The inhibiting effect of a higher octane number, means that the fuel burns slower when you do ignite it. This means you need to advance the timing to ensure the burn occurs at the correct time.
You should in general use the lowest octane rated fuel that your car will run on. There is no advantage to using higher ratings unless you have modified the engine in some way, plus it costs more. I believe the justification for charging more for the higher octane rated fuel (beside being a good tax ruse), is that the chemicals added to boost the level are more environmentally dodgy.
BTW - Octane of 100 is the performance level of pure octane (saturated hydocarbon with 8 carbon atoms in a chain).
Hope this helps. This is the theory, so I would suggest any perceived improvement is psychological or down to other additives. The premium petrols also tend to contain additional cleaning agents that keep the injectors in good shape.
If there is real interest, perhaps we could ask someone from Esso, Shell or BP to write an article for PP?
Rgds, Stuart.
It is a measure of the fuels knock resistance, that is, its ability to resist pre-ignition. You want the fuel/air mixture to ignite when you apply the spark, so that you have control over the timing and the flame front (since you know when and where in the cylinder the burn will start).
The ignition may occur due to the heat created by the compression, as in a diesel engine, if the octane rating is too low. The higher the compression ratio, the more heat is generated by compression and the higher the likelihood of pre-ignition.
The inhibiting effect of a higher octane number, means that the fuel burns slower when you do ignite it. This means you need to advance the timing to ensure the burn occurs at the correct time.
You should in general use the lowest octane rated fuel that your car will run on. There is no advantage to using higher ratings unless you have modified the engine in some way, plus it costs more. I believe the justification for charging more for the higher octane rated fuel (beside being a good tax ruse), is that the chemicals added to boost the level are more environmentally dodgy.
BTW - Octane of 100 is the performance level of pure octane (saturated hydocarbon with 8 carbon atoms in a chain).
Hope this helps. This is the theory, so I would suggest any perceived improvement is psychological or down to other additives. The premium petrols also tend to contain additional cleaning agents that keep the injectors in good shape.
If there is real interest, perhaps we could ask someone from Esso, Shell or BP to write an article for PP?
Rgds, Stuart.
As I understood it the higher the octane the more ignition advance you could run safely (due to the more predictable burning qualities avoiding pre-ignition) and generally more ignition advance (to the point of pre-ignition) equals more efficient combustion equals more power or better economy.
Cars with knock sensors should be able to take advantage of higher octane though without mods the range of advance is limited, (to cover 95 - 98 ?) so you may / may not notice the difference.
Tony
Cars with knock sensors should be able to take advantage of higher octane though without mods the range of advance is limited, (to cover 95 - 98 ?) so you may / may not notice the difference.
Tony
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New member
This is where things are not quite so straight forward.
Efficient combustion only occurs if you have enough time.
What happens at 3500 rpm on no load is rather different to what happens at 7000 rpm at full load trying to set a new personal best at warp factor ten.
Clearly at twice the rpm the time for the fuel to burn is halved.
If you look at top fuel dragsters you can see (from the flames out the exhausts) that a significant amount of combustion occurs outside the combustion chamber. On a road car this is not desireable (or legal) and shows it is running rich (which strains the cat if it had one).
You have the added complication of variable valve timing and the resonance that occurs in the inlet tracts as well.
The knock sensors and the and valves/valve seals on any recent Porsche means it can cope with either fuel, but which give the max performance is not so clear.
A little knowledge is dangerous, so I will defer to someone whose job it is to know such things. Hence my previous suggestion.
Rgds, Stuart.
Efficient combustion only occurs if you have enough time.
What happens at 3500 rpm on no load is rather different to what happens at 7000 rpm at full load trying to set a new personal best at warp factor ten.
Clearly at twice the rpm the time for the fuel to burn is halved.
If you look at top fuel dragsters you can see (from the flames out the exhausts) that a significant amount of combustion occurs outside the combustion chamber. On a road car this is not desireable (or legal) and shows it is running rich (which strains the cat if it had one).
You have the added complication of variable valve timing and the resonance that occurs in the inlet tracts as well.
The knock sensors and the and valves/valve seals on any recent Porsche means it can cope with either fuel, but which give the max performance is not so clear.
A little knowledge is dangerous, so I will defer to someone whose job it is to know such things. Hence my previous suggestion.
Rgds, Stuart.
yes, agreed it is a complicated area. I thought with dragsters they run pretty wild cam profiles as well with lots of valve overlap which also will give you flames in the exhaust, it is good for power, bad for economy and emissions.
I do however have a practical example of octane boosting - my company runs a prodrive africa subaru imprezza WRX in Botswana where the fuel is around 93, it hates it (it wants 95 minimum), it has flat spots everywhere and power is limited. Using toluene as suggested on the website above to approx 98 (experimenting with 95 first) the flat spots are gone and it produces much more power, (you have to disconnect the battery with the subaru to reset the management otherwise the knock sensor only very slowly advances the ignition).
In Africa toluene is much easier to come by and to store, than it is likely to be here.
My other direct experience, though again not with a Porsche - though I think my turbo runs better on 98 than 95 (it could be feelgood factor) but turbo engines are more likely to suffer pre-ignition - Iused to own a 1380 Mini, when this engine was first installed I ran pretty close to standard ignition advance to avoid pre-ignition- it had a higher compression ratio than standard, however with the cam installed more advance was desirable, when I had it rolling road tuned they found about 15Bhp by advancing the ignition timing.
Tony
PS I wish I did have the complication of variable valve timing!
I do however have a practical example of octane boosting - my company runs a prodrive africa subaru imprezza WRX in Botswana where the fuel is around 93, it hates it (it wants 95 minimum), it has flat spots everywhere and power is limited. Using toluene as suggested on the website above to approx 98 (experimenting with 95 first) the flat spots are gone and it produces much more power, (you have to disconnect the battery with the subaru to reset the management otherwise the knock sensor only very slowly advances the ignition).
In Africa toluene is much easier to come by and to store, than it is likely to be here.
My other direct experience, though again not with a Porsche - though I think my turbo runs better on 98 than 95 (it could be feelgood factor) but turbo engines are more likely to suffer pre-ignition - Iused to own a 1380 Mini, when this engine was first installed I ran pretty close to standard ignition advance to avoid pre-ignition- it had a higher compression ratio than standard, however with the cam installed more advance was desirable, when I had it rolling road tuned they found about 15Bhp by advancing the ignition timing.
Tony
PS I wish I did have the complication of variable valve timing!
Guest
New member
I think it could be that the toluene is giving increased power, and as a side effect is raising the octane value.
With a turbo, unless you have intercooloers, the air going into the cylinder is hotter than that witha normally aspirated engine, so pre-ignition is more likely.
I have a 200SX (2 litre turbo) which is set to run on 95. Subjectively when using Optimax it seems to gives a bit more torque in the mid range, but less thrust above 5000 rpm.
Rgds, Stuart.
With a turbo, unless you have intercooloers, the air going into the cylinder is hotter than that witha normally aspirated engine, so pre-ignition is more likely.
I have a 200SX (2 litre turbo) which is set to run on 95. Subjectively when using Optimax it seems to gives a bit more torque in the mid range, but less thrust above 5000 rpm.
Rgds, Stuart.
I have used octane boosters previously and have felt absolutely no difference in performance. I bought some booster from Demon Tweeks which claimed it added 2 RON points - I was using 97 at the time so technically I should have had 99 RON sloshing around in the tank. When it was delivered it came in a plastic bottle and then inside another plastic container as it is apparently that toxic. A nice way to waste a few pounds if you ask me - never mind.[]
See you at JZ tomorrow morning.
Rich
]See you at JZ tomorrow morning.
Rich
Guest
New member
We' re going round in circles. I don' t think we have the full picture.
I come back to my original point, we ought to get someone who knows to contribute. We should get someone from Shell, BP, Esso to explain what all this means in PP (assuming there are no industrial secrets).
I have been trawling the web and have not found any evidence that octane boosters will improve your performance, unless you are already losing power through pinking (from changing the cam profiles, turbo pressure, etc.).
Rgds, Stuart.
I come back to my original point, we ought to get someone who knows to contribute. We should get someone from Shell, BP, Esso to explain what all this means in PP (assuming there are no industrial secrets).
I have been trawling the web and have not found any evidence that octane boosters will improve your performance, unless you are already losing power through pinking (from changing the cam profiles, turbo pressure, etc.).
Rgds, Stuart.
ClubSport 911
New member
Stuart - you are right. Some couple of yrs back, I did a virtual thesis on the whole Fuel thing - I was running a Honda accord Type R back then, and was having pre-ignition problems, so spent yonks on the internet and phone to BP, shell etc to discuss / discover the issues associated with power, pinking, combustion and so on.
It' s complicated, and awfully " techie" .
I can only agree than in a car like ours (Porsche' s) then the state of tune is (thankfully) quite mild, so we' re not actually pushing combustion to the limit. 98 Optimax works well, as I suspect do other SUL concoctions.
I vote we get someone from BP / Shell to review the posts and then prepare a nice little white paper on what makes sense for us all.
FYI - my Accord was producing (no turbo) 230bhp flywheel with 2157cc. Compare with 231bhp from 3164 and you see the difference in state of tune, and demands made on combustion speed and effectiveness.
Ps - living 2.5miles from Santa Pod, I' m pretty sure I could distill Nitro Methane from the fumes in the atmosphere, and port them into my tank - what a thought.
It' s complicated, and awfully " techie" .
I can only agree than in a car like ours (Porsche' s) then the state of tune is (thankfully) quite mild, so we' re not actually pushing combustion to the limit. 98 Optimax works well, as I suspect do other SUL concoctions.
I vote we get someone from BP / Shell to review the posts and then prepare a nice little white paper on what makes sense for us all.
FYI - my Accord was producing (no turbo) 230bhp flywheel with 2157cc. Compare with 231bhp from 3164 and you see the difference in state of tune, and demands made on combustion speed and effectiveness.
Ps - living 2.5miles from Santa Pod, I' m pretty sure I could distill Nitro Methane from the fumes in the atmosphere, and port them into my tank - what a thought.
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