Octane rating - such a difference
Discussion
Took the Cerb out for a run today, having been apart for a few months, but it wasn't running great. Then I rembered on the way back from the garage last week I had to get some fuel as I was getting very low and pulled in to an ESSO garage. Highest octane they had was 97, so I only half filled the tank. The car did run but was not overjoyed, normally I always run it on Texaco or Optimax.
This morning it was very cold and the engine kept cutting out. Then after a 10 minute run to warm her up, I parked close to my house and then couldn't restart her at all. Recalling the lower octane fuel the previous week and all my experience of TVR ownership - firstly I had a cup of tea, then I went to the local garage and filled 2 petrol cans with Texaco Super (98 octane) and put them in the tank. She started first time, if a little lumpy at first
So I took her for a good blat and en-route filled her with a good dose of Optimax. Since then no problems. Running very smoothly and started and restarted all day as much I liked.
I can understand the car not running so well on a lower octane but I was not expecting a non starter when starting from hot. Has any one else had a similar experience or can explain why this would happen ??
From now on ONLY the good stuff for my Cerb.
This morning it was very cold and the engine kept cutting out. Then after a 10 minute run to warm her up, I parked close to my house and then couldn't restart her at all. Recalling the lower octane fuel the previous week and all my experience of TVR ownership - firstly I had a cup of tea, then I went to the local garage and filled 2 petrol cans with Texaco Super (98 octane) and put them in the tank. She started first time, if a little lumpy at first
So I took her for a good blat and en-route filled her with a good dose of Optimax. Since then no problems. Running very smoothly and started and restarted all day as much I liked. I can understand the car not running so well on a lower octane but I was not expecting a non starter when starting from hot. Has any one else had a similar experience or can explain why this would happen ??
From now on ONLY the good stuff for my Cerb.
Not sure there is any difference between running 95 and 98. Its possible to make both engines knock depending if you put the engine under the right stress at the right time, although obviously slightly more prone with the 95. And of course you get SLIGHTLY more power outta the higher octane
The ECU is adaptive. The adaption is additive. Meaning if you quickly swap from 98 to 95 or the other way round then the car will get upset untill it relearns what your doing. That may take more than one tank of fuel. So probably more important to stick to a particular fuel than swap around.
However progressive throttle on a hot engine rather than flooring it, and watch the load in low gears at low revs.
The ECU is adaptive. The adaption is additive. Meaning if you quickly swap from 98 to 95 or the other way round then the car will get upset untill it relearns what your doing. That may take more than one tank of fuel. So probably more important to stick to a particular fuel than swap around.
However progressive throttle on a hot engine rather than flooring it, and watch the load in low gears at low revs.
The ignition is not adaptive, so there is no power to be gained from 97/98 vs 95 unless the engine was mapped for this in the first place. There is no knock sensor. The fuel adaptive mapping is mainly for emissions.
The higher compressions red-rose cars get around this with the user-selectable map.
I very much doubt your issue had anything to do with the fuel!
The higher compressions red-rose cars get around this with the user-selectable map.
I very much doubt your issue had anything to do with the fuel!
Thanks for the input guys. Maybe it was a symptom of being kept outside for the last 10 weeks at the garage rather than the fuel. It was protected from the worst of the elements but maybe some condensation in the electrics was the cause which the drive helped to dry out. Although, I have to say, the difference to the running when the higher octane was added was almost immediate.
dannylt said:
The ignition is not adaptive, so there is no power to be gained from 97/98 vs 95 unless the engine was mapped for this in the first place. There is no knock sensor. The fuel adaptive mapping is mainly for emissions.
The higher compressions red-rose cars get around this with the user-selectable map.
I very much doubt your issue had anything to do with the fuel!
I have to disagree. I certainly would agree that the igition is not adaptive, and true again that there is no antiknock sensor on a Cerb, hence its overegged fuel map. But I contend that you will here a lot of drivers on this forum say that they have noticed big changes in the 'happiness' of their car when switching from one fuel octance rating to another. I suggest this is due to the fuel adaptives. If you disagree with this, to what do you consider it due?
Julian64 said:
The ignition is not adaptive, so there is no power to be gained from 97/98 vs 95 unless the engine was mapped for this in the first place. There is no knock sensor. The fuel adaptive mapping is mainly for emissions.
The higher compressions red-rose cars get around this with the user-selectable map.
I very much doubt your issue had anything to do with the fuel!
I have to disagree. I certainly would agree that the igition is not adaptive, and true again that there is no antiknock sensor on a Cerb, hence its overegged fuel map. But I contend that you will here a lot of drivers on this forum say that they have noticed big changes in the 'happiness' of their car when switching from one fuel octance rating to another. I suggest this is due to the fuel adaptives. If you disagree with this, to what do you consider it due?
I agree with danny.
i would say partly it's placebo effect and partly that lesser fuels burn in a different way. Unleaded fuels are hard to ignite and burn fiercely once ignited, it's the *quality* of the combustion that you're maybe feeling? there's no reason why they should produce different power outputs though bearing in mind you need about 30plus bhp in a cerbera to notice any difference in performance at all!
If you do a search on fuels on here , look for posts by people *in the know* .. they'll tell you that there's no such thing as different fuel brands in their entirety as such .. they're all blended with only a few properly independant fuel types. Optimax is a proper fuel type in it's own right, and it's detergent properties are well documented, as well as it's 98plus octane rating when fresh, however the octane rating in itself will have nothing to do with the perceived smoothness, but it's burn quality may well have.
i would think the unhappy cerbera in this case was purely coincidental.
Placebo effect mostly? I agree that the higher octane can reduce the high-load low-rev knock etc., but the extra power (and responsiveness) comes mainly from the ignition, and this simply is not changing.
There was a big difference in my Cerbera with the 97 map over the 95 one, and that was easier to check because you could switch it to and fro.
Having said that, I'm sure you get even more difference just by having it mapped properly in the first place! I've just had the acceleration enrichment tweaked on my MBE Caterham map, and the difference is incredible.
>> Edited by dannylt on Monday 21st February 15:02
There was a big difference in my Cerbera with the 97 map over the 95 one, and that was easier to check because you could switch it to and fro.
Having said that, I'm sure you get even more difference just by having it mapped properly in the first place! I've just had the acceleration enrichment tweaked on my MBE Caterham map, and the difference is incredible.
>> Edited by dannylt on Monday 21st February 15:02
joospeed said:
dannylt said:
The ignition is not adaptive, so there is no power to be gained from 97/98 vs 95 unless the engine was mapped for this in the first place. There is no knock sensor. The fuel adaptive mapping is mainly for emissions.
The higher compressions red-rose cars get around this with the user-selectable map.
I very much doubt your issue had anything to do with the fuel!
I have to disagree. I certainly would agree that the igition is not adaptive, and true again that there is no antiknock sensor on a Cerb, hence its overegged fuel map. But I contend that you will here a lot of drivers on this forum say that they have noticed big changes in the 'happiness' of their car when switching from one fuel octance rating to another. I suggest this is due to the fuel adaptives. If you disagree with this, to what do you consider it due?
I agree with danny.
i would say partly it's placebo effect and partly that lesser fuels burn in a different way. Unleaded fuels are hard to ignite and burn fiercely once ignited, it's the *quality* of the combustion that you're maybe feeling? there's no reason why they should produce different power outputs though bearing in mind you need about 30plus bhp in a cerbera to notice any difference in performance at all!
If you do a search on fuels on here , look for posts by people *in the know* .. they'll tell you that there's no such thing as different fuel brands in their entirety as such .. they're all blended with only a few properly independant fuel types. Optimax is a proper fuel type in it's own right, and it's detergent properties are well documented, as well as it's 98plus octane rating when fresh, however the octane rating in itself will have nothing to do with the perceived smoothness, but it's burn quality may well have.
i would think the unhappy cerbera in this case was purely coincidental.
I think I said in my first post there was nothing to be gained in power, and in that I agree with dannyit, but do you think all the people who have posted saying they have noticed a difference in engine running when changing fuels are noticing a co-incidently change?
Julian64 said:I really think it's mostly a placebo effect. Especially seeing as you pay more for the higher octane fuel! Unless you're comparing it with really crap fuel which we've all had once in a while.
I think I said in my first post there was nothing to be gained in power, and in that I agree with dannyit, but do you think all the people who have posted saying they have noticed a difference in engine running when changing fuels are noticing a co-incidently change?
Well, I admit I run my car on regular unleaded, so I agree with posts that it doesn't make much difference.
However the specific problems posted on here time and time again seem to be people who have always ran on this or that, who suddenly make a change and report a drastic change to the smooth running of their car.
I can't help thinking there has to be a cause to this and that it can't be simply co-incidental. The only explination I could think of were the adaptives.
When I had my (sorry Jules's) ECU apart the adaptives would slowly change when they were on the bench disconnected from their environment, but only very slowly and incrementally. This made sense to me.
However the specific problems posted on here time and time again seem to be people who have always ran on this or that, who suddenly make a change and report a drastic change to the smooth running of their car.
I can't help thinking there has to be a cause to this and that it can't be simply co-incidental. The only explination I could think of were the adaptives.
When I had my (sorry Jules's) ECU apart the adaptives would slowly change when they were on the bench disconnected from their environment, but only very slowly and incrementally. This made sense to me.
Just to add my bit to this...surely if you have a tank of mixed fuel, (95 and 98 ron) then difference would be not be noticable...I cant say that when I have added some 95 unleaded to existing optimax in the tank, that I have noticed any difference at all!
Having said this, I do on all occasions, except in emergency's, run Optimax.
Having said this, I do on all occasions, except in emergency's, run Optimax.
To say there are no distict Brands of fuel is not really true. Fuel made by BP, Shell, ConocoPhillips(Jet) etc will all have slightly different charactaristics as each Refinery will have slightly different components all of differing quailities. They are the blended together to meet the minimum specifications detailed in BS EN228 (95 RON) other properties such as density, MON and Vapor Pressure also have a significant effect on a fuels overall performance.
One thing you must be aware of is the fact that all fuel producers in the UK have exchange agreements which in effect means that all the fuel available at all branded filling stations will be supplied from the nearest refinery regardless of the company. This is to save on costs and the logistics of moving millions of gallons of fuel around the country.
The one exception is Optimax which is soley produced by Shell. This is a high octane, low density, low aromatics fuel with extra detergent addatives. The low density and aromaticity make it a very "clean" burning fuel. Hence good throttle response and anti-knock tendancies. The only downside is all other things being equal you fuel economy will suffer slightly due to the lower density but who cares about that!!!
One thing you must be aware of is the fact that all fuel producers in the UK have exchange agreements which in effect means that all the fuel available at all branded filling stations will be supplied from the nearest refinery regardless of the company. This is to save on costs and the logistics of moving millions of gallons of fuel around the country.
The one exception is Optimax which is soley produced by Shell. This is a high octane, low density, low aromatics fuel with extra detergent addatives. The low density and aromaticity make it a very "clean" burning fuel. Hence good throttle response and anti-knock tendancies. The only downside is all other things being equal you fuel economy will suffer slightly due to the lower density but who cares about that!!!
Gassing Station | Cerbera | Top of Page | What's New | My Stuff