Fuel money saving idea - use super unleaded?

anewman

Now the fuel prices are going up and up, with super keeping a similar price above the unleaded, the super is becoming a better buy. All credit for this idea to Rob Clubley at Briskoda.net but just thought I would post the idea with some examples for discussion here where money saving matters :cool:.

For example, from petrolprices.com at my local Sainsburys, unleaded is 110.9 and super is 113.9. Super costs just under 3% more. Therefore, to make super worthwhile, you only need to gain 3% or more in mpg. For example, if on unleaded you get 40mpg, you need to get around 42mpg or more to make super unleaded worthwhile.

Another example. Petrolprices.com again, local Tesco. Unleaded 112.9 super unleaded 117.9, super unleaded is just under 4.5% more. If you get 40mpg, around 42mpg or more is needed to make the super worthwhile over the standard unleaded.

Hopefully I got all my maths correct - but I do not know if these sort of MPG gains are possible in most road cars with super unleaded. But hopefully this can be the start of helpful discussion and maybe even some user testing of MPG on different fuels.

In theory, most modern cars since around 1994 have ECU's which can learn and adapt to various changes in the car, including an increase in the fuel's RON, so theoretically these cars should see reduced fuel consumption.

LandyAndy

The handbook for my Mazda RX-8 specifically says that there is no advantage to be gained from using higher octane fuels whether for consumption or performance.

I don't think extra performance from my lightweight is an issue.:D

davetrousers

An interesting idea. I shall follow this thread with interest.

Have you got a link to the thread on Briskoda?

photome

I just thought one burnt hotter than the other, but didnt think there was any difference in mpg...I may be wrong of course

davetrousers

They do claim better mileage on the sales blurb on garage forecourts.

bryanb

Compression ratios, ignition systems, and fuel injectors are set up for a particular grade of fuel. Using the wrong grade will cause damage.

anewman

davetrousers wrote: »

Have you got a link to the thread on Briskoda?

http://briskoda.net/forums/roadside-hotel/how-fast-fuel-prices-going-up-near-you/111510/4/#post1301768

anewman

davetrousers wrote: »

They do claim better mileage on the sales blurb on garage forecourts.

They also claim the super unleaded is "suitable for all unleaded cars"

meester

The average is 115p vs 122p. I.e. 6%.

It is correct that the price differential is less now in relative terms.

I believe it depends a lot on the engine. US gasoline is only about 91 RON, whereas in the UK it is RON 95. Thus a US engine should be less likely to require high-octane fuel. Whereas the Japanese standard is 99 RON, hence performance Japanese cars, and a few high-compression engines including motorbikes do need high-octane fuel, 99% of cars don't.

Super ranges between RON 97 and RON 102.

BTW, for the ecofreaks, super unleaded has been shown by government research NOT to be more damaging than regular unleaded, hence the tax is the same.

My personal judgement is that super unleaded is a waste of money, because there are NO proper published and controlled studies showing that it improves fuel consumption, and any personally conducted ones are likely to be fatally flawed by subtle changes to driving style, different road conditions, etc. I think most people buying it are just buying into marketing, partly from the manufacturers who like people to think they are buying a super-engineered vehicle that requires special fuel.

Until I see a proper study to show any improvement whatsoever, I am saving my cash.

I would certainly not go anywhere near it if the manufacturer does not specify in the manual that they recommend fuel of higher than 95 octane, and even then I would only consider it.

thescouselander

There is no harm in using super unleaded but you may or may not see any benefit depending on weather your car can make the adjustments needed to take advantage of the higher octane fuel.

Higher octane fuel is less susceptible to detonation meaning that higher compression ratios can be run and the ignition timing can be advanced. You are most likely to notice a difference if you have a turbocharged car. In the case of the RX8 - it uses a relatively low compression ratio so no gain will be seen.

Personally, for the cars I've owned, I've never seen and improvement in performance or MPG when using super unleaded.

anewman

This thing about compression is interesting. My car was available in two flavours. Both 1.3 litre but one low compression with 54bhp, the other a high compression with 67bhp - both recommend the same type of fuel. I have the high compression version so wonder if it would see any sort of benefit.

I guess another possible benefit of super unleaded is extra added cleaners? - saves on adding redex?