Unleaded v SuperUnleaded

anewman

michaelro wrote: »

Depends on the car.

Low Powered - Don't bother
High Powered - I would (And have when I owned one)
Japanese Import - Definitely (+ have it mapped to UK Fuel)

Not sure these rules apply. VW and Skoda recommend 98RON for the 1.4l 16v engine. Relatively powerful for the displacement, but not in relation to other engines out there.

petrolhead69

I`ve tried super unleaded/v-power/ultimate/optimax in every car I`ve had and only ever felt a difference in 3 cars, slight difference in a saab 2.3 turbo, slight difference in a 3.2 merc CLK and an enourmous difference in my current Audi A4 1.8T. in the A4 the difference in power and smoothness is so good even my wife noticed, and she can drive a micra on 3 cylinders and not realise somethings amiss. A4 gets roughly 2-3 mpg more as you can shortshift more due to the improved driveability.
You need to suck it and see.

michaelro

michaelro wrote: »

Depends on the car.

Low Powered - Don't bother
High Powered - I would (And have when I owned one)
Japanese Import - Definitely (+ have it mapped to UK Fuel)

anewman wrote: »

Not sure these rules apply. VW and Skoda recommend 98RON for the 1.4l 16v engine. Relatively powerful for the displacement, but not in relation to other engines out there.

Apart from that particular engine and a few others like it, any car with less than say 180bhp would unlikely benefit greatly from using Super Unleaded.

From what I've read about that particular engine and the 1.6 is that if it isn't run on 98RON it's unlikely to last past than 60k....:eek:

harveybobbles

I've started running mine on the more expensive diesel, not gained any power, but the tank seems to last about 60-90 miles more than it did on normal derv.

Paradigm

Taken from my cars handbook.....

Recommended fuel grade 98 RON. Note, use of 95 RON in ambient temperatures above 75deg may result in some loss of engine power.

Lemonade_Pockets

As above most cars it makes b*gger all difference.

I've run a few cars (renaultsports) where it felt marginally better, crisper performance etc but i'm not sure how much of that was psychological. It did return a better MPG which just about covered the surplus charge for the stuff.

In my current car a cooper S it doesn't seem to make any diff what so ever.

The only car i genuinely noticed was a scooby which ran like a bag of spanners on 95. A few friends have a the same issue with TVR's and porsches.

Colin_London

Having just got a new car I was reading the handbook section on Fuel, and it made it absolutely clear that using a higher RON fuel than necessary produces absolutely no performance improvement.

However, there is no problem with using a RON number higher than your car is designed for... obviously execpt for the loss of £s from your pocket.

The only absolute no-no is using a RON of less than required by your manufacturer. So if you have an older car that requires 98 RON then you really should try and avoid 95 RON.

AdrianHi

harveybobbles wrote: »

I've started running mine on the more expensive diesel, not gained any power, but the tank seems to last about 60-90 miles more than it did on normal derv.

Ah now diesel fuel is a different story and I find the same as you.
BP ultimate Diesel, Shell V Power or anyones "standard" diesel plus some Millers diesel fuel treament (they keep changing the name of it) improves economy by around 5% to 7%. These are then minimum 55 cetane raiting fuels - maximum usefull.

Shells standard diesel is actually equivalent to Total Excellium at minimum 53 cetane rating , everyone elses "standard" diesel minimum cetane rating 51.
So if you routinely use Shell standard diesel you will not see so much improvement.
Cetane index/number/rating = a measure of how well the diesel fuel burns.

Goldenyears

Some of the improvement you get going from 95RON to 98/99 RON might be just because there is more of it ! The toluene octane improver that is added to 95RON petrol increases the density by about 4%. If we metered fuel by kilo and measured consumption by kg per100 km things would slightly different, more significantly for diesel. Only half the diesel/petrol difference in mpg is due to real thermal efficiency gain.

tomstickland

Super unleaded has a higher Octane rating and a slightly lower specific energy value.
The higher Octane means that it resists knocking (auto ignition) more, so higher compression ratios or more timing advance or more boost are possible.
So it will help performance on some engines and might give slightly better mpg if the timing advances enough.

For most people it isn't worth the extra money.