High Octane?

  • Some time ago I came across a discussion somewhere about using high grade fuel.
    The suggestion was that, using Shell V power or equivalent actually increased mpg thus offsetting the extra £/L. but still giving better performance and a cleaner engine.
    The ECU is supposed to recognise the higher octane and adjust accordingly.
    I didn't act on this as the car I had then was a boring Laguna.

    Daughter, who has a Focus ST225 was recommended to do this last week by her b/f who has a Scooby. He reckons it is true for the Scooby and even more so for his Yamaha R1!
    So she has put some Shell V in the tank and is convinced she is getting more mpg. (or maybe she is brainwashed by love?) :roll:

    Any thoughts mx-3 wise?

  • Our ECUs use the knock sensor to advance timing on the fly. Higher octane = less knock. So performance increase in theory is possible, performance also sits hand in hand with effeciency (NA). I remember filling up on BP ultimate and getting fantastic mileage, but I've never really tried consistant tests. But remember UK fuel is already relatively high octane, though not compared to Japan… I think some Jspec scooberpoos literally have to be ran on premium or they go boom.

  • Based on what you say Marco I will give this a go. I am nearly empty at the moment (indicated so not really, as from 'empty' I only ever put 7-8 gallons in to fill her).
    I have pretty well kept all receipts and mileages per fill-up since I got the car last August so will be able to compare.
    I don't thrash around much these days and currently get around 30mpg or a little bit more.
    Petrol is 94.9/L round here and I think Shell V or BP Ultimate are 101.9 so the increase in mpg better be good.

    I assume it will take a couple of fill-ups to clear the lower octane out and get pure high octane in the tank.
    I will come back in due course with results.

    Just a thought….
    Are V and Ultimate basically the same so I don't have to run about finding one or the other?

  • I'm somewhat sceptical but very interested to hear your results! I'm not 100% on this but it may be worthwhile resetting your ECU so it can learn to use a more aggressive ignition timing. Anyone any knowledge on this? I know it works on my dads 95 volvo 2.3T estate :lol:

  • reseting it in the fult code list remove a fuse for so long

  • Always used high octane in Scooby, makes for a smoother engine on them. Same as the CBR it loves the stuff but my NSR prefers normal. Use high octane on track aswell..


  • @3daaecec49=james:

    reseting it in the fult code list remove a fuse for so long

    Not sure what you mean here. James. Is there someting I should do?

  • always use it in the boat and the jet ski
    and did in the mx3
    and always noticed a difference. makes it smoother and more responsive
    dont do it for diesels though lol

  • All an octane rating is in petrol is an indication of the amount of chemicals added to the fuel to control the burn rate of petrol. The higher the octane rating, the slower and more controled the burn of the fuel. It doesn't have anything to do with increasing the power output of your engine.

    The reason higher octane fuel may benefit your car or bike is all to do with the compression ratio of your engine. If you have a high compression engine, like a sports bike or Turbo'd car you want to be able to control the burn of the fuel mix and prevent detonation (pre-ignition) The higher octane rated fuel does this as it has certain chemicals in it (what exactly I don't know) to help control that burn. Lower octain fuels might detonate before it's ignited by the spark plug in a high compression engine.

    Addatives like Nitrox hot shot and similar (that claim to increase engine power output) only increase the octane rating. Not good for Joe boy racer in his 1.2 Corsa!! :lol: These addatives have been proven to reduce power output.

    Marco is right though. If the higher Octane fuel does reduce knock in the engine. The ECU might be able to push out more power from the higher octane.

    I guess my basic point is don't think that a higher ocatne fuel in your car will automaticly give you better performance.

    A little bit I've taken from the Car Bibles that explains it 10 times better than me!

    Octane and power
    It's a common misconception amongst car enthusiasts that higher octane = more power. This is simply not true. The myth arose because of sportier vehicles requiring higher octane fuels. Without understanding why, a certain section of the car subculture decided that this was because higher octane petrol meant higher power.
    The reality of the situation is a little different. Power is limited by the maximum amount of fuel-air mixture that can be jammed into the combustion chamber. Because high performance engines operate with high compression ratios they are more likely to suffer from detonation and so to compensate, they need a higher octane fuel to control the burn. So yes, sports cars do need high octane fuel, but it's not because the octane rating is somehow giving more power. It's because it's required because the engine develops more power because of its design.
    There is a direct correlation between the compression ratio of an engine and its fuel octane requirements. The following table is a rough guide to octane values per engine compression ratio for a carburettor engine without engine management. For modern fuel-injected cars with advanced engine management systems, these values are lowered by about 5 to 7 points.

    Compression ratio Octane
    5:1 72
    6:1 81
    7:1 87
    8:1 92
    9:1 96
    10:1 100
    11:1 104
    12:1 108

    Octane and gas mileage
    Here's a good question : can octane affect gas mileage. The short answer is absolutely, yes it can, but not for the reasons you might think. The octane value of a fuel itself has nothing to do with how much potential energy the fuel has, or how cleanly or efficiently it burns. All it does is control the burn. However, if you're running with a petrol that isn't the octane rating recommended for your car, you could lose gas mileage. Why? Lets say your manufacturers handbook recommends that you run 87 octane fuel in your car but you fill it with 85 instead, trying to save some money on filling up. Your car will still work just fine because the engine management system will be detecting knock and retarding the ignition timing to compensate. And that's the key. By changing the ignition timing, you could be losing efficiency in the engine, which could translate into worse gas mileage. Again as a practical example, my little tale above about our trip to Vegas on low octane gas. (Whether you want to believe some bloke on the internet or not is up to you). On the low octane gas on the trip down, we could barely get 23.5mpg out of the Subaru. Once I was able to fill it up again with premium at the recommended octane rating, we got 27.9mpg on the way back. A difference of 4.4mpg over 450 miles of driving.
    Doing the maths, you can figure out that by skimping on the price during fill-up, you may save a little money right there and then, but it costs in the long term because you're going to be filling up more often to do the same mileage. My advice? Do what the handbook tells you. After all it's in the manufacturers better interests that you get the most performance out of your car as you can - they don't want you badmouthing them, and in this day and age of instant internet gratification, you can bad-mouth a large company very quickly and get a lot of publicity.

    Octane boosters

    In some extreme cases, the highest octane fuel available might not solve a knocking or detonation problem. That's normally a symptom of a deeper problem in the engine involving carbon deposits on the cylinder heads, bad spark timing, faulty engine management systems or similar. In these cases, some people choose to add octane booster to their petrol. Basically you fill the tank as normal, then put in a measured amount of octane booster and it further raises the octane level in an attempt to stop the detonation. One of the downsides of this is that it can make the engine harder to start from cold, because the octane booster has made the fuel so much less volatile that it's hard to get it to ignite on the first couple of strokes. Products like Klotz and Redex octane boosters are readily available over the counter in most auto parts stores. Octane boosters are typically used by mis-educated motorcyclists who believe the myth (explained above) that high octane = more power.
    Octane boosters tested by Fifth Gear. To try to lay the myth about octane boosters giving more power to bed for once and for all, in 2007 the UK TV show Fifth Gear picked four likely candidates and subjected them to rigorous testing. They picked Nitro Hot Shot, NOS Race Only Octane Booster, Wynn's Power Booster and STP Power Booster. All four products make the usual wild claims about increased gas mileage, more bhp and so on and so forth. They took the products to Oxford Brooks University's engine testing lab. The engine was static-mounted so measurements were made at the flywheel. The throttle was computer controlled so they could reproduce the same scenario over and over again. They first did a baseline test to find out peak bhp with regular unleaded petrol. This involved various constant-throttle settings as well as acceleration and deceleration testing, and a 1-hour constant-speed run to emulate driving on a motorway in clear traffic. Each product was tested using the identical setup, with a 15 minute 'pure' petrol flush being used in between each test to ensure there was no cross-contamination. The results were interesting. Nitrox Hot Shot, NOS Race Only Octane Booster and Wynn's Octane Booster all reduced the overall power by 2bhp. STP Power Booster reduced it by 6%. Now remember this was measured at the flywheel so by the time you induce all the drag of the gearbox and driveline into that equation, you'd likely be looking at a 5% to 10% drop at the wheels. Impressive results for products that claim to increase your engine's power.

    Full page here

  • This is something different but well worth reading. It was written by a learned friend in Stoke and i think it maybe is of interest to any car or bike owner.

    Well…………! In The Beginning there was Carbon and Hydrogen.

    These got together in accordance with rules forged in the Big Bang (yes, really!) to make methane, one carbon atom with 4 hydrogen's stuck on.

    A bit later, (only 4000 million years) other atoms started getting together and finally came up with Life, a self-reproducing chemical mix. The reproducing bit was quite fun, but after 600 million years even that gets boring.

    So, a more or less intelligent life-form invented The Car and the Motorcycle, the ultimate boredom cure. This was, and is, powered by the Internal Combustion Engine, which must have fuel.

    Methane is a fuel, which means it burns in air to produce energy, but unfortunately it’s a gas; a tank-full would propel a Honda 50 for about half a mile.

    But! Methane had not been idle since the formation of planet Earth, and had joined up with more carbons and hydrogen's to make chains called ‘hydrocarbons’. Well, they were'nt called that at the time. They had to wait for a life-form to evolve that liked giving things names, and a hundred and 20-odd years ago chemists had to learn Latin, so they called the one with five carbons ‘pentane’, the 6-carbon one ‘hexane’, then ‘heptane’ then ….wait for it…. the 8-carbon one ‘octane’ and so on. (If we were naming them now the last one would be called ‘eightane’ so you would need 95 minimum REN for your engine.)

    All these things were liquids, very thin and volatile, and pure concentrated energy. The Hildebrand and Wolfmuller (rough 1894 equivalent of the Honda 50) now did 100 miles to the tank full.

    Unlike water, these liquids don’t stand around in lakes. They are hidden underground in porous rock so you have to drill for them. The old name was ‘petroleum’ meaning ‘rock oil’ but this was soon shortened to ‘petrol’. The petrol came out of the wells mixed with heavy oil, so it had to be distilled off in an oil refinery.

    Early on, the pale coloured stuff that evaporated easily and caught fire very easily was sold as internal combustion engine fuel. It was a simple as that. ‘Octane Number’ hadn’t been invented, but in modern terms this ‘light petroleum fraction’ was about 50 Octane. Now we all know that in the GCSE Science engine The Piston squeezes the air/fuel mixture, then The Spark Plug ignites it to produce The Power Stroke.

    The trouble is, with 50 octane fuel if The Piston squeezes too much the heat generated by compression makes the stuff Go Bang prematurely before The Spark Plug gets a look in, giving a Power Stroke with as much push as a fairy’s fart. This is why early engines couldn’t use compression ratios above 4 : 1, and 10BHP per litre was seen as hot stuff.

    Engines improved but petrol didn’t and even some time after WW 1 a touring 1000cc engine only turned out about 25BHP, and a hot-shot Sport version with the latest overhead valves would need a good tuner to get 50BHP.

    So finally some effort was made to stop primitive petrol going bang too soon, and a variable compression engine was invented for research. (The ‘CFR’ engine, as used for finding Research and Motor Octane Numbers, RON and MON, to this very day.) Early on researchers found that the bung in the CFR head could be really screwed down if a heavy liquid called ‘TEL’ (tetra ethyl lead) was added. This was really effective and cheap, and allowed the ‘straight’ petrol to be upped to 90 or even 100 octane, and a whole load of exciting high-power engines were designed around these fuels.

    This leaded fuel survived into the late 1990s, but much earlier an amazing discovery had been made. The shape of the petrol molecules was very important. ‘Octane’ if the ‘straight eight’ version with 8 carbons in a row had an ‘octane number’ of 25. It was only the mutant octane with 5 carbons down the middle and the others sticking out from the sides that gave the best results at high compression. (This special octane is still used as a standard for 100 octane. Proper name is 2,2,4-trimethyl pentane.)

    Today, ‘petrol’ is really a synthetic fluid built up from oil industry feedstocks. Very little of it is unmodified distillate from crude oil. It is tailor made to include the best compression-resisting molecules so that no poisonous and polluting lead compounds are needed to reach 95 or even 98 octane. Nothing much is added, apart from a touch of detergent to keep the engine top end clean. Quite a lot of petrol now has 5% ‘renewable’ alcohol as a planet-saving gesture, but this also improves the octane number (by about 1 ) so there’s nothing wrong with that.

    Anyway, if you have a motoring holiday instead of flying ComaJet, you are keeping that carbon footprint down….and paying too much tax as well…..but that’s another story.

    Fascinating stuff….

  • Thanks for replies/opinions guys. Much appreciated.

    I am not so interested in performance improvement, what intrigues me is mpg.

    So we will see. Nearly showing empty so will be filling up with V on Friday I reckon.

    Incidentally, what is the compression ratio for the v6?

  • i always but escos lol
    i know its sounds funny
    but pretty sure its the highest pump ocatne fuel you can buy
    at 99

  • BP ultimate 102 - available in about 10 places in UK^

  • @b7bac1ecc5=Rod:

    Incidentally, what is the compression ratio for the v6?

    9.2:1 for k8

  • Tescos do!!

    "Many of the large petrol companies have launched 'super fuels' - petrols and diesels that have a higher research octane level. These fuels are said to increase power in many vehicles, deliver less pollution than regular fuels and help to maintain a cleaner engine. Amongst these 'super fuels' are Tesco's Super Unleaded 99 Octane petrol, supplied by Greenergy, now sold at many stations across the UK and also BP's Ultimate 102 Unleaded which is currently the most advanced, high-performance petrol you can buy on UK forecourts. "

  • @06b95f7af4=Marco:


    Incidentally, what is the compression ratio for the v6?

    9.2:1 for k8

    Wiki suggests 9.4. But not much difference really.


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