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My wife has a ten year old Honda Shuttle (2.3 VTEC). She always puts in the cheapest petrol and was quite cross when I treated the motor to Super Unleaded fuel. But isn't better fuel supposed to help old engines? Can anyone explain the technical difference that justifies the price difference in the petrol? Cheers
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The benefit of Super Unleaded is that the fuel company makes bigger profits.
There is a good layman's explanation about fuel types here:
www.petrolprices.com/about-fuel.html
....and here:
tinyurl.com/kn4jgv link to wiki.answers.com shortened to restore page width to normal
Edited by Dynamic Dave on 13/07/2009 at 01:10
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It depends on which brand of Super Unleaded that is used. If, for example, BP Ultimate or Shell V Power is used then an engine may well benefit from their stronger cleaning agents compared with a brand that only adds an octane improver. BP Ultimate is proven to increase mpg per tankful in like for like driving conditions.
Super Unleaded will provide increased performance for many engines/cars but some drivers/people don't appreciate the benefits.
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My Prelude Vtec definitely does a few more mpg on 98 unleaded although it runs perfectly happily on 95. I use 98 all the time here in France but it's only a cent or two per litre dearer than 95.
ps: IMHO an old Honda engine equals the engine in any newer but ordinary car...
Edited by mike hannon on 13/07/2009 at 07:20
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Certain high performance cars change the mixture when they detect higher-octane fuel. As such, they run better on the higher octane "super unleaded".
Otherwise, it's like the difference between buying Persil and Tesco's own brand washing powder. Who knows...
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What the linked explanation misses is that cleaner running at low revs for whatever reason allows you to use higher gears and lower revs and has a beneficial effect on fuel consumed. You won't get better economy if you drive exactly the same. But you will if you use higher gears and lower revs than you can on ordinary premium unleaded.
HJ
Edited by Honestjohn on 13/07/2009 at 12:28
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We used to sprinkle half a cup full of petrol onto a bonfire we had each weekend at the back of the garage.
Four star ignited, but five star nearly exploded.
I'm no scientist, but it seemed obvious the higher octane fuel produced more 'power'.
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I'm no scientist but it seemed obvious the higher octane fuel produced more 'power'.
As explained here tinyurl.com/mg2eyq the octane rating of petrol is not fundamentally linked to the energy content.
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..he octane rating of petrol is not fundamentally linked to the energy content...
OK, I'll rephrase that.
The stuff with four stars on the pump flared when lit.
The stuff with five stars written on the pump went whooomph! and singed your eyebrows.
Transfer that to a combustion chamber, and common sense tells me the engine using five star will produce more grunt.
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Transfer that to a combustion chamber and common sense tells me the engine using five star will produce more grunt.
In a combustion chamber the petrol/air mixture burns in a controlled way, with the flame starting from the spark plug and propagating through the mixture as the piston moves. Spontaneous combustion (detonation) produces "knock" and subsequent damage. Setting fire to petrol is an uncontrolled and random process and can't be compared with what happens in a combustion chamber.
wapedia.mobi/en/Four-stroke_cycle
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>>What the linked explanation misses is that you will if you use higher gears and lower
>>revs than you can on ordinary premium unleaded.
Are you suggesting in all seriousness that all cars benefit from running on Super?
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Surely, if your engine runs properly at low rpm - see mention of Honda above, for example - anyone can get better mpg by using higher gears and lower revs, no matter what fuel you put in?
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Supermarine/Rolls Royce learned in the 1940s that you could increase boost pressure with higher octane fuels.
Tests I've seen which show an increase in bhp have almost always been on high performance cars with turbos.
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I'd agree with that statement. I have a slightly tuned Saab 93 Turbo. It holds boost for longer with higher octane fuel. It will run OK on lower octane fuel, particularly if the ambeint temp is cool, but it can go into anti-knock mode and lower the maximum boost that the turbo will run. It can be seen quite clearly on the Turbo boost gauge.
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We normally use Shell or Esso 95 RON in our non-turbo Forester.
A couple of weeks ago the missus filled it up from a BP station on an almost empty tank - wow what a difference, the engine is quieter, smoother and pulls better from low revs .
Occasionaly I give the Subaru a treat with some Tesco 99 or V-Power, and I have to say the regular BP stuff feels as good, but without the extra cost.
MVP
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it makes the sheiks richer
the govt richer
the oil companies richer
the advertisers richer
the pump owner richer
and makes you poorer,however seeing as you need super unleaded in your choice of car,just give us the money
signed a shieks friend...............
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My Hyundai i30 Comfort seems to run smoother on Super, which I have tried experimentally. This probably means less engine wear but I can't say I've noticed better mileage. (Today's price at my local Shell station is 103.9p against 99.9p for the kitchen variety.)
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I've no idea if it makes cars run better, but we treat the Harley Sportsters to the occasional tankful; seems to give the carb a bit of a clean-out and perks 'em up a bit, especially if one of 'em's been running a bit sluggishly.
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Mrs P's MK5 Golf GTi was run from new on Shell Optimax - the manual was quite specific about running FSI engines on this fuel. Cheapskates who run FSIs on 95 RON fuel can expect problems according to this very website. All three bikes run on the specified 95 stuff.
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Supermarine/Rolls Royce learned in the 1940s that you could increase boost pressure with higher octane fuels.
>>
That's surely the point at issue - "could increase the boost pressure" means modifications could be made to take advantage of the higher octane rating. That's not the same thing as saying you will get more power or economy from an unmodified engine merely by using a higher octane fuel.
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It depends on whether the engine has to retard the ignition, to run without preignition with 95 Ron petrol. Many do IIRC. The main benefit of higher octane seems to be low end and mid-range rpm. BTW, the WW2 Merlin etc engines ran on 150 octane when it became available:)
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Now here's a thing. No science implied mind. What's more, I'm telling a tale about diesel so I'm on the wrong thread anyway but it might interest some and at least amuse others....
A regular ( too bloomin' regular at the mo' ) run I make is from my house into central London and back in a day. A round trip of 336 miles. What a bore but I still haven't got a proper job......
Armed with my trusty old Mondeo 111 diesel estate I fill her up every night on my return ready for the thrills of the following day. I've done that trip six times in the last two weeks. Always on weekdays, always at the same ungodly early hour of the morning and returned at the same evening rush time as all the other motorway lemmings each night. Each time it has taken me 3 hours on the button outbound and 3 hours 20 minutes to come back.
The first five trips were on standard diesel and cost more or less £45 to refill to first click.
Anyway, last night I was empty and filled the car up with V-power diesel for a lark. Same journey times so I assume same speeds or thereabouts. Car was noticeably smoother and as HJ said re the posh petrol, seemed less in need of downshifts. The killer though, especially given that the good stuff is 7p a litre more to buy was that when I filled up again tonight with the single malt diesel it came to £39.90
Like I said, no science in this. Just interesting I thought. I shall try this stuff for a while and monitor its cost effect at least. As for performance, I can't say but it certainly felt better on a subjective level anyway.
Edited by Humph Backbridge on 13/07/2009 at 23:35
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That is a really interesting answer - along with all the others, thanks a lot everyone. As it was Tesco Super Unleaded at least I can now reassure the missus by telling her it is supplied by Greenenergy and therefore kinder to the environment! B.
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... I shall try this stuff for a while and monitor its cost effect at least. As for performance, I can't say but it certainly felt better on a subjective level anyway....
Humph,
We'll get you on the Millers yet.
I reckon super diesel or Millers is worthwhile in older engines - it worked in my last Focus.
Not sure that I'm getting the same benefit with the CC3.
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Forget superunleaded, what you need is one of these:
tinyurl.com/mn5dqg
If I fit two, will I gain 70bhp? :-)
Edited by nick on 14/07/2009 at 11:32
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My test of the quality of fuel is the run up the A3 onto the Hoggs Back at Guildford.
If I have good fuel I can poodle up at 55 ish in 5th gear, if the fuel is poor quality I have to downshift to 4th.
What HJ says is correct, the biggest difference I can detect is the improved torque at low revs.
MVP
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