Discussion
Hello all,
When I was getting the work done on my car yesterday, Roger at Monkfish told me I’d be using poor fuel and this had effected the car’s engine management as it had closed itself down, to protect itself against this poor fuel. I told him I only used V-Power (formerly Optimax) from Shell and he said that was the cause of it. Because of the way Shell is made, if it sits in the garage tank or your car’s tank for anything more than a day or 2, it can start to “go off” and in modern engines, they will shut themselves off to a degree to protect them from poor fuel. The reading I had done on fuel in the past, highlighted Shell’s premium as best and he reckons that in a race (F1) situation, which is where they developed this fuel from, it probably is the best. But if you’re not running the car so often or you buy fuel from an out of the way garage with not a very high turnover, then chances are the fuel will have turned. It’s only at its best if its new in both the garage and your tank.
His solution was either BP Ultimate or would you believe it, Tesco Premium. They’ve never had any issues on cars that run on BP ultimate and in his opinion (and not withstanding the refinery issue earlier this year) Tesco premium fuel. I have not used the Tesco fuel as yet, but am switching over to BP as of yesterday to keep the performance of my car at its best after the work was done on it. I will trial Tesco when I need my next tank, so probably Thursday in that case as I only filled up yesterday ;-)
When I was getting the work done on my car yesterday, Roger at Monkfish told me I’d be using poor fuel and this had effected the car’s engine management as it had closed itself down, to protect itself against this poor fuel. I told him I only used V-Power (formerly Optimax) from Shell and he said that was the cause of it. Because of the way Shell is made, if it sits in the garage tank or your car’s tank for anything more than a day or 2, it can start to “go off” and in modern engines, they will shut themselves off to a degree to protect them from poor fuel. The reading I had done on fuel in the past, highlighted Shell’s premium as best and he reckons that in a race (F1) situation, which is where they developed this fuel from, it probably is the best. But if you’re not running the car so often or you buy fuel from an out of the way garage with not a very high turnover, then chances are the fuel will have turned. It’s only at its best if its new in both the garage and your tank.
His solution was either BP Ultimate or would you believe it, Tesco Premium. They’ve never had any issues on cars that run on BP ultimate and in his opinion (and not withstanding the refinery issue earlier this year) Tesco premium fuel. I have not used the Tesco fuel as yet, but am switching over to BP as of yesterday to keep the performance of my car at its best after the work was done on it. I will trial Tesco when I need my next tank, so probably Thursday in that case as I only filled up yesterday ;-)
I knew that fuel could go 'off' to a degree, but I didn't realise that it took days rather than weeks?!! When you say 'shut down', do you mean that the ignition timing is being retarded for safety? Up to now I've also run exclusively on V-Power from shell, but may try the Tesco 99 stuff just to see what difference it makes if any. Maybe I can blame a poor performance at Pod recently on bad fuel lol.
Why is it only V-Power that's effected by this, and not other high octane fuels?
Why is it only V-Power that's effected by this, and not other high octane fuels?
monkfish1 said:
For clarity; i said it backs off from the optimum setting, in the same manner as if you puyt 95ron fuel in. It doesn't "close down". Car continues to function just fine.
Edited by monkfish1 on Tuesday 12th August 12:35
Pretty ignorant about modern engine management systems, so perhaps a stupid question, but does this system automatically return to the optimum setting when you put some decent fuel in. At one time wasn't it a question of disconnecting the battery in order to restore all settings to standard? Do these cars have dual spark maps - high/low octane or again, have things moved on?
Am interested since my VXR8 developed a problem recently whilst in Spain. Started missing slightly at low revs if under load. Obviously easy enough to drive around the problem but some time later when I let the revs drop all seemed to be well and no problems subsequently. Could be many issues causing the miss but did wonder if I had picked up a rough tank of fuel and the ECU had adapted to it.
Need to get myself a scantool to see if I can find out what was going on. Any thoughts - a steep learning curve with EFILive or make do with a more basic tool? I don't really see myself modifying the car so is the full EFILive package a bit over the top?
Yes it will scale up and down, they still have dual spark maps even on the vxr8. A reset will put you right back on the top one. You used to be able to change the rate of adjustment too, so it recovers faster. Ive not checked that on the latest one yet. If you want to accept all risks and mess with stuff yourself you can make high and low octane tables the same. (this is done sometimes over a limited timescale for tuning to keep variables at a minimum) Though Im not suggesting anyone does this as a matter of course.
FYI The VT/VX GTS-R HSV 300KW had both tables set to the same values from HSV off the showroom floor.
FYI The VT/VX GTS-R HSV 300KW had both tables set to the same values from HSV off the showroom floor.
Quick fuel lesson - The RON number is the fuel's resistance to knock (pinking). The higher the number, the more resistance.
To get the most BHP you need to advance the spark as far as possible (the spark plug is ignited before the piston gets to the top of the cylinder) (TDC) - maximum cylinder pressure should be around 12 degrees before TDC).
If you advance the spark too far you will get knock. A higher RON fuel will allow more advance without knock and therefore more BHP. The engine is also fitted with sensors than 'hear' knock and will retard the timing to suit.
When its remapped your engine may detect knock when another loaded with the same data did not, this could be due to a number of factors but the most likely is a low grade RON - whether its 'gone off' or just a bad batch is debatable.
Tesco super is 99RON, BP Ultimate is 97, Shell Optiblah is 98. Regular unleaded is 95. BP also sell a 102RON in selected stations - you would need a custom map to take full advantage of this (and deep pockets at £2.50/litre!). Both BP and Shell contain additives that remove carbon deposits from inside the engine, give you more MPG etc etc blah blah.
Personally I use Tesco as its cheaper!
To get the most BHP you need to advance the spark as far as possible (the spark plug is ignited before the piston gets to the top of the cylinder) (TDC) - maximum cylinder pressure should be around 12 degrees before TDC).
If you advance the spark too far you will get knock. A higher RON fuel will allow more advance without knock and therefore more BHP. The engine is also fitted with sensors than 'hear' knock and will retard the timing to suit.
When its remapped your engine may detect knock when another loaded with the same data did not, this could be due to a number of factors but the most likely is a low grade RON - whether its 'gone off' or just a bad batch is debatable.
Tesco super is 99RON, BP Ultimate is 97, Shell Optiblah is 98. Regular unleaded is 95. BP also sell a 102RON in selected stations - you would need a custom map to take full advantage of this (and deep pockets at £2.50/litre!). Both BP and Shell contain additives that remove carbon deposits from inside the engine, give you more MPG etc etc blah blah.
Personally I use Tesco as its cheaper!
bertelli_1 said:
To get the most BHP you need to advance the spark as far as possible (the spark plug is ignited before the piston gets to the top of the cylinder) (TDC) - maximum cylinder pressure should be around 12 degrees before TDC).
Incorrect information dude.Spark should be set to MBT which is not the same as "as far as possible". Also max pressure should be more like 14*ATDC, NOT BTDC unless you like smashing your engine up.
Also a higher octane is not always best, it depends on where MBT is and how far from the knock point this is. If its on or over knock point then yes higher octane will help by reducing knock and allowing timing to approach MBT without knock. But on a lower compression engine designed for standard fuel higher octane is a pointless waste of money and may actually decrease performance.
ringram said:
bertelli_1 said:
To get the most BHP you need to advance the spark as far as possible (the spark plug is ignited before the piston gets to the top of the cylinder) (TDC) - maximum cylinder pressure should be around 12 degrees before TDC).
Incorrect information dude.
Spark should be set to MBT which is not the same as "as far as possible". Also max pressure should be more like 14*ATDC, NOT BTDC unless you like smashing your engine up.
Also a higher octane is not always best, it depends on where MBT is and how far from the knock point this is. If its on or over knock point then yes higher octane will help by reducing knock and allowing timing to approach MBT without knock. But on a lower compression engine designed for standard fuel higher octane is a pointless waste of money and may actually decrease performance.
Also, MON (Motor Octane Number) is a better measure of a fuel's resistance to knock as it is measured under more severe load (higher revs) than RON. Ordinary unleaded usually has a MON of 85 where BP 102 and Shell V Power is 90 & 86.9 respectively. Reading the numbers this way it doesn't look much different? Add to that fuel's RON/MON rating falls due to olefinic breakdown as soon as it's exposed to air, hence the reaon race fuel is kept sealed until it is put in the tank.
When your ECU detects consistent knock due to high AI temps (hot sunny day) or poor fuel it will switch to different (base) tables that pull loads of timing out to protect the engine at the expense of power, this is especially true in FI engines. It will recover..eventually.
I'm no expert but I've learned that a slightly less agressive tune that avoids knock, albeit below MBT will give good performance on regular 95 unleaded at the expense of just a few hp. It's interesting that the compression ratio of FI engines is the same as the NA ones which says to me there's little to be gained from fancy fuel in a standard car?
The guys in the USA have rubbish fuel and they still manage 600+ rwhp so in summary, stop wasting money on expensive super unleaded and spend it instead on some decent air-through-the-engine mods that really make a difference.
Edited by anonymous-user on Wednesday 13th August 09:45
The USA is not rubbish fuel- theirs is advertised as the *average* of the RON and MON values where as ours is just the higher RON value.
It's essentially the same but our "95" is actually worse than their "93"
MON is the number you want to use for tuning.
Generally speaking the difference between 95 and 98 ron will not have any effect on NA engines. UK fuel is quite strictly tested (most bad batches are due to water getting into the storage tanks rather than the fuel itself) and you'll generally find 95 fuel not much different from 97.
The only other realy difference are the engine cleaning additives - Shell have confirmed that there are no difference in the additives accross their range (95, 97, optimax).
It's essentially the same but our "95" is actually worse than their "93"
MON is the number you want to use for tuning.
Generally speaking the difference between 95 and 98 ron will not have any effect on NA engines. UK fuel is quite strictly tested (most bad batches are due to water getting into the storage tanks rather than the fuel itself) and you'll generally find 95 fuel not much different from 97.
The only other realy difference are the engine cleaning additives - Shell have confirmed that there are no difference in the additives accross their range (95, 97, optimax).
Edited by ads_green on Wednesday 13th August 10:18
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