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| Thread ID: 62462 | 2005-10-08 08:44:00 | Did Shell change its petrol? | Nomad (952) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 394522 | 2005-10-09 00:08:00 | Have you noticed the wonderful typo in the headline? No, where? |
pctek (84) | ||
| 394523 | 2005-10-09 00:20:00 | No, where?Quesitons? :eek: | Tony (4941) | ||
| 394524 | 2005-10-09 03:06:00 | Might be the same in NZ as here, but Shell Oil Corp and Texaco are the same people now. I think the take-over was international..can't speak about your octane ratings though...ours are so messed up with the R+M/2 (Research + Method divided by 2) computation, we are happy to get 82 octane for just about anything. | SurferJoe46 (51) | ||
| 394525 | 2005-10-09 03:17:00 | I read somewhere that BP 98 octane was the bet petrol in NZ www.bpultimate.co.nz I have been using it and subjectivly it does seem better (really hard to tell though, as you put it in and expect it to be better, so your experience is biased by the hawthorne effect) |
netchicken (4843) | ||
| 394526 | 2005-10-09 03:49:00 | I read somewhere that BP 98 octane was the bet petrol in NZ www.bpultimate.co.nz I have been using it and subjectivly it does seem better (really hard to tell though, as you put it in and expect it to be better, so your experience is biased by the hawthorne effect) Basicly, unless an engine is designed/tuned to take advantage of a higher octane rating, ie higher compression ratio, more advanced ignition timing, then there is no point in going to higher octane petrol, there will be zilch difference in performance. |
Terry Porritt (14) | ||
| 394527 | 2005-10-09 03:49:00 | I read somewhere that BP 98 octane was the best petrol in NZ I've got a feeling that the inverse might apply, namely 98 is ok, but 91 has got worse . I have run 4 different Mazda 626 vehicles from mid 80's to mid 90's vintage on 91 for around 500,000km in total without problems, and about 9-12 months ago I suddenly began to experience pre-ignition (pinking) problems on load . I have always had my vehicles serviced by the local Mazda agent and when I queried the accuracy of their tuning, they insisted that 91 Octane has dropped in quality i . e . it is not true 91 . For a while they said that Gulf 91 had a better octane rating than Shell/BP/Caltex etc but I never noticed any difference . They later said that they couldn't (wouldn't) retard the timing any further than the recommended "91" setting so I've had to start using a 70/30 mix of 91/98 to get a rattle free existence . Has anybody else noticed a drop-off in the quality of 91? Cheers Billy 8-{) :confused: |
Billy T (70) | ||
| 394528 | 2005-10-09 04:01:00 | Personally, I haven't noticed any pinking with Regular 91. Perhaps a de-coke is called for ? I would be surprised if the octane rating was surreptitiously being reduced, I suppose the refiners could get a particular batch of petrol wrong though. It has been known to happen in the past. |
Terry Porritt (14) | ||
| 394529 | 2005-10-09 06:02:00 | I've got a feeling that the inverse might apply, namely 98 is ok, but 91 has got worse . I have run 4 different Mazda 626 vehicles from mid 80's to mid 90's vintage on 91 for around 500,000km in total without problems, and about 9-12 months ago I suddenly began to experience pre-ignition (pinking) problems on load . I have always had my vehicles serviced by the local Mazda agent and when I queried the accuracy of their tuning, they insisted that 91 Octane has dropped in quality i . e . it is not true 91 . For a while they said that Gulf 91 had a better octane rating than Shell/BP/Caltex etc but I never noticed any difference . They later said that they couldn't (wouldn't) retard the timing any further than the recommended "91" setting so I've had to start using a 70/30 mix of 91/98 to get a rattle free existence . Has anybody else noticed a drop-off in the quality of 91? Cheers Billy 8-{) :confused: I would find a good mechanic,who if need be would do as he was told . |
Cicero (40) | ||
| 394530 | 2005-10-09 06:04:00 | OK . . here's what's happening: The fact that gasoline (petrol) is more expensive than alcohol, means that there is going to be a lot of alcohol added to the fuel per gallon . You are getting a heavier dose of alcohol than before the "energy crisis" . What happens is this: (not getting into the economics of the situation here) Gasoline burns well at a 13 . 7:1 air:fuel ratio for good economy and power at sea level or 14 . 7 lbs/in square air pressure . . . that's what the computers and old carburetors were designed to deliver . Anything less or more was either wasteful or polluting or both . Now gasoline has a certain amount of calories in it (heat value when rapidly oxidized or burned) and when mixed with air (oxygen) in the proper amounts is supposedly considered by the EPA here in the US and whatever committee or department of the environment in NZ to be an "optomized" operating condition . Add alcohol . All values go out the window . In spite of it's seemingly explosive qualities, it actually delivers less heat or BTU's than gasoline . The ratio of air to alcohol is approximately 7:1 . What this means is that you use 7 parts air to 1 part alcohol by volume or weight again just to be equal to gasoline in BTU's . The ratios explain it best . If you have to use much more alcohol to just EQUAL the heat production of gasoline, then this is not a good trade-off . You are burning more (by volume or weight or mass . . . . whatever statute you use to compute the difference) fuel to perform the same work . The sad part is that at certain ratios of alcohol:gasoline there is a noticeable improvement of octane value because it absorbs the heat in the engine and keeps the temperature lower in the cylinder so there is less ping . . This "OCTANE VALUE" is the rate at which gasoline burns in a test engine over a range of loads/conditions up to the point of destructive pre-ignition . Prior to that, the engine just needs more fuel to compensate for lack of energy . You accomplish that by using more throttle (foot pedal action) or the computer enrichens the mixture by increasing injection time factors, elapsed injector "on" time and finally retarding the ignition to help keep the engine from destructive "knock" . Your EST (knock-sensor) device takes care of that problem . . but it costs you a lot of power (fuel) and performance (fuel again) . The octane requirements of most civilian-owned vehicles is internationally about 83 R+M/2 octane . There is some leeway in the field for lack of certain products to retard fuel flamefront percussion . . . the correct term is "ping" . If the fuel can self-ignite from the temperatures generated in normal compression or there is a glowing ember in the cylinder to ignite the fuel/air charge before the correct time, erratic flamefront propagation causes "shock waves" to travel across the top of the piston(s) and destroy the engine by breaking the piston, cracking the rings or pounding the rod bearings with shock loads outside of normal designs . To keep this from happening the oil companies process the fuels to a certan "octane" . Octane is the value of the fuel describing it's ability to NOT BURN . . . . . . . that is under adverse conditions or outside designed parameters . If a person were to put higher than necessary octane-rated fuel into their tanks, then they are just wasting fuel and having to make the engine work harder to deliver the same amount of power it is desigend to deliver with a lower octane fuel . A secondary problem with using higher than necessary octane is that the fuel is still burning when the exhaust valve(s) open and that prematurely burns the valve/valve seat and places undue strain on the catalytic convertor and the general exhaust system handling the excessive heat . (Have you ever felt the gobs of heat from the exhaust system?) The flame that could have been used to power the engine is just wasted and pumped out of the engine via the exhaust system and lost as unused energy . Gasohol is really a fraud and a waste of chemical engineers' talents . It is just to fatten the pockets of certain "Green-types" who, with severe ignorance, insist that their way is the best way . The waste and misuse of petro- chemicals and general dumb-ness of the population helps keep these myths alive . The energy used to produce and cook methanol (alcohol for gasoline mixtures) actually costs much more to produce than the energy it produces . John Q . Publik has no idea that he is using more energy than if he just used pure gasoline without all the special "formulations" demanded by some tree-hugger in some politician's face . Bio-mass fuels are not as efficient as good ol' gasoline . |
SurferJoe46 (51) | ||
| 394531 | 2005-10-09 08:54:00 | Diesel changes mean my twuck is now smokey, still heaps of grunt though, even if i am using more gas....... | personthingy (1670) | ||
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