I know its not an unknown thing that some engines sound quieter running on Super, Im asking really because Super UL makes a marked difference in the Ignis to how much mechanical noise the car makes, esp at idle and under load.
What is it that makes the noise, its sort of a thrashing sound that at speed sounds a bit like a hiss. I stuck a full tank of Super in today and after a few miles it had almost disappeared, but comes back as soon as I stick normal UL in.
Just curious what part of the engine it is the noise comes from and why the octane has such an effect. I used to notice the same thing on my Nubira, a car tuner told me it was because the engine didnt have to work as hard igniting the fuel, but it didnt actually explain the noise.
Yes, I have alot of time on my hands, wife is away in wild Norfolk :-)
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Super can make it feel smoother, though much less noisy, not so sure.
If the engine is electronically managed with anti knock sensors then super allows the ignition to be more advanced thus a little more power wil be produced and thus a littel less right foot needed at any given speed / rate of acceeration, perhaps that explains the apparent difference.
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Its all about burn time. The super burns later and shorter in the cycle, changing the noise the engine makes.
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Proper tinkling pinking or detonation is seldom heard from modern chip-managed engines, but might there not be a sort of borderline detonation going on with the ordinaire?
I haven't noticed any real difference with my present car. But then superjuice is so dear that I am too mean to give it a proper try.
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Would've thought you'd have swopped yours for a diesel somethingorother by now AC? Now you're out in the sticks and so on. Must be a ready source of hookey red stuff available in exchange for a sack of turnips or whatever you're growing in the top meadow this Spring surely?
:-)
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>> The super burns later and shorter in the cycle, >>
To the contrary it enables the ignition to advance so burns earlier though also burns a very little slower and at the same time more completely thus optimising the transfer of energy from combustion to rotation.
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Higher octaine fuels burn later in the cycle.
Higher octane ratings correlate to higher activation energies: This being the amount of applied energy required to initiate combustion. Since higher octane fuels have higher activation energy requirements, it is less likely that a given compression will cause uncontrolled ignition, otherwise known as autoignition or detonation.
It might seem odd that fuels with higher octane ratings are used in more powerful engines, since such fuels ignite less easily. However, detonation is undesirable in a spark ignition engine, and is signified by audible "pinking" or in more extreme cases "knock".
Last edited by: Zero on Mon 23 May 11 at 19:19
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>> Higher octaine fuels burn later in the cycle.
That reads like something penned by John Le Carre.
"...and there will be geese under Tower Bridge by midnight"
" we've been expecting you, you have the package?..."
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Higher octane ratings correlate to higher activation energies: This being the amount of applied energy required to initiate combustion. Since higher octane fuels have higher activation energy requirements, it is less likely that a given compression will cause uncontrolled ignition, otherwise known as autoignition or detonation.
It might seem odd that fuels with higher octane ratings are used in more powerful engines, since such fuels ignite less easily. However, detonation is undesirable in a spark ignition engine, and is signified by audible "pinking" or in more extreme cases "knock".
So, in a NON high compression engine it burns later in the cycle. You dont want it burning early you get pinking.
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The compression ratio on my car is 11.0 :1
No clue what that means or whether its relevant!
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Had a Smart Roadster and that ran far better on super, but cant really say I have noticed any difference in anything else
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Z, you could say that with an engine that does not have anti knock sensors and is not able to advance and retard the ignition to account for fuel quality the super u/l burns later, though only because it burns slightly slower.
However in the majority of modern engines it will be ignited earlier be cause the engine will be able to run more with the ignition more advanced.
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>> whatever.
>>
You are saying the same thing but looking at different aspects.
Higher octane is more difficult to ignite as is less prone to pre-ignition, so therefore the controlled ignition, ie the spark, can be adjusted to occur earlier.
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>> The compression ratio on my car is 11.0 :1
>>
>> No clue what that means or whether its relevant!
>>
That is the capacity of the swept volume v the capacity of the combustion chamber, i.e. the piston is trying to compress 11x the volume of the combustion chamber into it (at atmospheric pressure) before the compressed charge is ignited.
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... and in the old carburettor days would have been regarded as a very high, competition-type compression ratio. Rollses and American cars in the forties were often 7 to 1 or less. High-performance saloons in Europe were 8 to 1 or a bit over. There were exceptions of course.
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watchdog or top gear tested the super duper stuff and it was found to be worse than the regular stuff !!! its probably just peoples imagination running away with them
my car always feels like its running great when i leave the MOT station with a branny (mot certificate)
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Ive found it gives a few mpg more and torque improves in the mid-range, its very noticeable in my car, but hasnt made much odds in others, so unless you test it with every car, theres no way of saying whether it works or not.
In my car it seems to have a genuine effect, when I went back to standard UL I thought there was something wrong with the car, but only if you drive the same car, on the same roads each day are you likely to notice it.
Theres a steep NSL hill out of the town I live in which really shows up a lack of power and on Super it doesnt loose any speed, infact I often have to lift off slightly whereas on normal I found I was burying the throttle more than I was used to having switched back from Super, it was starting to irritate.
Im certain its the fuel simply because thats the only thing which changed from this morning to this afternoon and even with my work gear in the car it was tugging that bit harder than it had been on the way to work.
Given Watchdog and Top Gear are about sensationalism rather than actual fact based investigations, I wont loose any sleep over their findings.
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Interesting stuff. Ive got Tesco 99 in my car atm and its is marginally better than the Sainsburys Super UL. I get those 5p a litre off vouchers atm so I can get it at 133.9 a litre atm, not too pricey ( all things being relative! ).
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My M3 needed 98 Octance fuel and would pink noticeably if I used anything with a lower Octane rating. This happened when I was touring Southern Italy once where 98 Octane fuel was like hens' teeth and I was forced to fill up with 95 Octane.
In the UK it suffered pinking when I filled with Super Unleaded (98 Octane) which led me to wonder whether the Super Unleaded in the UK was always met the Octance rating or not.
The jungle juice 99 - 102 Octane fuels made no difference to performance or economy.
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Got overtaken by an Ignis Sport a few days ago. They're rare round these parts. Even rarer to find someone getting a proper shift on around our (pretty decent) B roads. Pretty much made my day.
Must have had a tiger in his tank to paraphrase Bb & the old adverts.
For a relatively tall and wide car, there was no discernable roll going round a bend at ~75mph.
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>>For a relatively tall and wide car, there was no discernable roll going round a bend at ~75mph.<<
Indeed there isnt. Im wondering whether I can get some poly bushes to replace the originals as they are prob past their best now.
The speed it can carry through a bend still makes me smile now, on sweeping s-bends it is immense, it must be a heck of a trackday car, esp on some serious tyres.
Its lowered 50mm over the standard car, so its sort of like a lowered 4x4 stance, but its so light the height makes little odds. Love it, esp the rasp when the variable valve comes in at 3000 rpm, it sounds alot like an alfa twin spark.
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>> watchdog or top gear tested the super duper stuff and it was found to be worse than the regular stuff !!! >>
Remember this Fifth Gear test?
www.youtube.com/watch?v=4boT3iwgZKI
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"Higher octane ratings correlate to higher activation energies: This being the amount of applied energy required to initiate combustion. "
You do talk a lot of twaddle, at times, zero.
The amount of energy supplied as a spark is fixed! The car does not vary that. It is the same regardless of what petrol you use.
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"You do talk a lot of twaddle, at times, zero.
Never!
Zero is alway right. Is it not written? Has he not told us so? So many doubters and unbelievers
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Zero possibly means that the propensity to misfire, present in all spark ignition engines, is greater for a given spark error rate in a high compression DI engine on lean mixture without fuzzy neural ignition timing control. See.
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>> "You do talk a lot of twaddle, at times, zero.
>>
>> Never!
>>
>> Zero is alway right. Is it not written? Has he not told us so? So
>> many doubters and unbelievers
Not seen me claiming the world would end last Saturday now have you.
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>>Not seen me claiming the world would end last Saturday now have you. <<
I assumed you were the high priest behind the old codger and his bible...
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Right now I would be arguing the world really did end, and all the people questioning me were in hell and didn't yet know it, not some crap excuse that I got my dates wrong.
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Think you could be set for a PR role for end of the world fanatics.
To give the fella his due though, J-witnesses have been knocking on my door telling me how the day is coming for years, but atleast they dont say when - smart.
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"Right now I would be arguing the world really did end, and all the people questioning me were in hell and didn't yet know it"
Truly wise words. I shall record them in The Book
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>> "Higher octane ratings correlate to higher activation energies: This being the amount of applied energy
>> required to initiate combustion. "
>>
>> You do talk a lot of twaddle, at times, zero.
Not me, thats what A petrol company said, I think they know more about than you or I, plus they didn't take a tiny bit out of context.
Last edited by: Zero on Tue 24 May 11 at 21:06
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"Higher octane ratings correlate to higher activation energies. . ."
I may be wrong, (get that in quick on eer, now) but I think that relates to burning the fuel at high compression rather than its ignition. Highly compressed fuel-air is much easier to light, you have more molecules per CC and so more released energy per cc. Hence needing anti-knock to stop it going bang.
As to ignition, I studied and built test rigs to repeat the experiments of earlier peers, and then designed and tested various ignition systems (Inductive, capacitor discharge etc), in real motorcars, for their in/adequacy. Not quite back to Davy and his safety lamp and going down the mine, though. The short conclusion:
An ignition coil produces a voltage that is adequate to spark the plug. That voltage is (1) much higher when foot is to floor than (2) when foot is off, or nearly off, the accelerator -- low compression.
The required energy input to the coil from the battery is thus determined by (1) and spark duration time. Whilst it would be possible to reduce it for condition (2) the extra complication and reduced reliability does not warrent the saving of the few watts.
As to altering the spark energy according to fuel type used, if the spark occurs and the system has been designed properly, in terms of coil and plug, the mixture lights. Not much scope to alter things.
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Going back to Stu's original observation - my old Civic VTi would pink under moderately high load (eg. accelerating up a reasonably steep hill at 35-40 in top (~2000rpm) with 95RON and tended not to do it running Optimax (the V-Power of the day).
11:1 is a very high compression for a petrol engine in the UK - surprised it only puts out 110bhp or so with VVT, but maybe the car was also sold in Japan where higher RON fuel is the norm?
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100 octane "race fuel", which is MSA compliant - just means it can't use any ingredients which don't appear in forecourt fuel, although you can vary the relative quantities - £4.40 / litre!
In some ways that's a lot cheaper than i expected but in other ways... ouch!
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Go to any 'historic' race meeting and see the fuels available.
105 octane anyone (I wonder if it's leaded)?
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Been running the Kenari on that Tesco Momentum 99 stuff in the last 4 weeks and its really made a difference.
Saw my first 45 mpg average from a tank this afternoon, going back to normal 95 saw it plummet to 38.5 and then back up again on the good stuff.
Its about 6p a litre more, but the car does feel much smoother, not sure if the extra mpg makes it more expensive, neutral or a gain. Regardless, my car seems to have expensive tastes, well above its Aldi credentials.
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I once mistakenly put Super U/L in my Prelude, it was (istr) about 5p per litre dearer than ordinary U/L, and at the time I was rather mad at my carelessness, but after a couple of miles I started noticing the difference, and after that I never ran on anything else!
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45 vs 38.5 is a 17% decrease in consumption, whereas 6p is only a 4.3% increase in cost (on 140p / litre). ergo you appear to be around 13% better off with the super.
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Job done then, thanks for doing the maths, im way too stupid for that kind of thing :-)
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I definitely notice a difference in range on the odd occasion I don't put superunleaded in the A4 (which, with the 2.0T engine is supposed to run on 98 octane or higher), but not to the extent of going 17% further. From full to the warning light coming on is around 440 miles usually; that'll be nearer 400 on ordinary unleaded. Premium costs around 5% more, so even going 8% further is worth it in my book, never mind the fact that it 'feels' happier on it. There again, I don't have many datatpoints really; I can (somewhat sadly possibly) count on the fingers of one hand the number of times it has had a tank full of regular
Interestingly the premium for super over ordinary is unchanged over the last 4 years or so (which as long as we've had the A4); still around 7p/litre, and so it's relatively better value now than in 2007!
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When i had my Smart Roadster it ran far better and gave better MPG of the super stuff - sounded (even more) like a bag of nails on standard 95 octane.
The A3 I had after didn't really notice any difference
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Why is my engine quieter on Super UL? - Hard Cheese
