Super unleaded - is it worth the extra cost?

[funkyrobot]

I changed from a diesel car to a petrol one in September and am now used to the green pump. Now that I take notice of this colour of pump, i've wondered whether or not I should invest in the other green pump, the super unleaded one.

I have a 57 plate Mazda 3 sport which states on the filler cap 'unleaded, minimum 95 ron', which is obviously the standard unleaded. But i've been wondering whether I really should be using the higher octane fuel?

So, is it worth me using super from now on? And what are the benefits? I've heard that the fuel burns better so you get better consumption, and the car performs slightly better, but are these claims true?

Thanks all.

[davepoth]

Depends on the car really. If it has a knock sensor and automatically adjusts the timing according to the fuel octane then yes, there's a point. If not you are throwing money away.

[matchmaker]

You have stirred up a hornets nest here..........I can only speak for my own car, an Octavia vRS. In the handbook and in the filler cap 98 RON is recommended. I run it on Tesco 99 RON. If I use 95 RON I notice a loss of power and worse fuel consumption.

[funkyrobot]

matchmaker said:

You have stirred up a hornets nest here..........I can only speak for my own car, an Octavia vRS. In the handbook and in the filler cap 98 RON is recommended. I run it on Tesco 99 RON. If I use 95 RON I notice a loss of power and worse fuel consumption.

st. Sorry. Don't want this to turn into a fuel slagging match. I just wondered if it would make a difference to my car. Maybe I should investigate further myself.

[evolution666]

it is if it specifically states your car has to run on it.

When the first engine let go in my Subaru, that was one of the first things they looked at and probably the first thing they questioned me about. They claimed to have taken a sample from the tank. If they can get out of warranty repairs any possible way, ive learnt theres no level they wont stop to

[jbi]

whats your engine compression ratio?

Higher compression motors tend to require the higher octane stuff to prevent pre-ignition.

Most modern cars will automatically adjust for the petrol you put in but fuel economy and power output can suffer if you regularly use the wrong stuff.

Edited by jbi on Tuesday 21st December 13:32

[thinfourth2]

If turboed and meant to run on it then have higher octane fuel.

If not turboed or tuned to run on it then go for 95Ron


I know that i will be called all sorts for what i am about to say.

A engine tuned for 95 octane will make LESS power on 98 octane as 98 octane fuel has a slightly lower calorifc value.

i know my caterham goes very slightly quicker on 95 octane

But 98 octane costs more so i must be wrong

[AJB]

matchmaker said:

I can only speak for my own car, an Octavia vRS. In the handbook and in the filler cap 98 RON is recommended. I run it on Tesco 99 RON. If I use 95 RON I notice a loss of power and worse fuel consumption.

This is the key. If the handbook says you have to use 98 (or greater), then you have to use it. If the handbook recommends it, then you'll probably get better fuel economy and power by using it, and it's probably worth the extra money. If the handbook just says 95 is fine then although, depending on the car, you might get very slighly better fuel economy or performance it probably won't make much difference, and probably isn't worth it. And in many cars recommending 95, using 98 or 99 won't make any difference at all - it'll just cost more.

eta What thinfourth2 says makes sense too - if it's designed/optimised for 95 then 98 could give slightly worse performance in some cars.

Edited by AJB on Tuesday 21st December 13:37

Edited by AJB on Tuesday 21st December 13:39

[swamp]

My car's handbook says 98 RON, but I normally use 97 RON because that is all you can get most places. In fact I've never seen 98 RON, only 99 in Tesco.

[funkyrobot]

Thanks all. I'll double check my handbook. The fuel flap (mentioned above) says min 95 RON to maybe I should just stick to this.

[TVRleigh_BBWR]

thinfourth2 said:

Said stuff and
A engine tuned for 95 octane will make LESS power on 98 octane as 98 octane fuel has a slightly lower calorifc value.

They tested this on one of the motoring programs and found what you just said to be true.

[Elskeggso]

Pinking can happen on some cars if 98ron isn't used IIRC.

[FranKinFezza]

funkyrobot said:

Thanks all. I'll double check my handbook. The fuel flap (mentioned above) says min 95 RON to maybe I should just stick to this.

If the maker recomends 95 for that car then there is no real advantage
in you using higher.

As the other posters have said its only going to make a difference
to cars designed to run with it. In your case it may well not only
cost you more but your cars economy may well actually be worse thus costing
you more still so

unless you are stuck in the middle of nowhere at a forcourt thats run out of
95 then don't bother.

[5lab]

I'm not sure about this 'better fuel economy' side of things. More power, yes, as more air and fuel can be added - however surely the economy would only possibly be in the same way that a chip can have better economy by letting you use a lower gear for longer (which is minimal improvement)?

Above is written with an assumption that there is a knock sensor and related ignition advancing gubbins.

[pilchardthecat]

It's about 7p/l (5-6%) more expensive, but i get maybe an extra 20 miles out of a 50l tank (which is about 7%) so they both cost the same, pretty much

My car is happy on 95, but you can notice the difference in power delivery between 5k and 8k rpm (s54b32 engine)

Garages vary price wise, sometimes super is 9p+ more than 95, so i'll get 95, sometimes it's closer (typically supermarkets and shell are 4p or 5p) so i'll get super.

Just because the manual says "95 minimum" doesn't mean there's no benefit from higher octane, although the engine mgt will need knock sensors

Edited by pilchardthecat on Tuesday 21st December 14:08

[AJB]

5lab said:

I'm not sure about this 'better fuel economy' side of things. More power, yes, as more air and fuel can be added - however surely the economy would only possibly be in the same way that a chip can have better economy by letting you use a lower gear for longer (which is minimal improvement)?

Above is written with an assumption that there is a knock sensor and related ignition advancing gubbins.

I don't quite understand what you're getting at? The knock sensor is the whole point. If the engine has a knock sensor, then it fine-tunes the timing of the spark to (just) avoid knock. Advancing the spark so it happens a little bit earlier in the cycle increases power and economy, but advance it too much and you get knocking (very bad for the engine).

Higher octane fuel allows higher compression ratio, or more advanced spark without knocking. This is why, with a knock sensor, higher octane fuel can give better performance and economy if the engine's map is designed to allow for it as the ecu realises it can advance the spark more.

Without a knock sensor, nothing will be adjusted. Either the engine needs 98 (in which case it will knock using 95) or it doesn't (in which case you lose a bit of power on 98 as it's got a lower calorific value).

If the engine does have a knock sensor, then it might be optimised for 95 (in which case it can adjust slightly when using 98, but not much and you don't get much extra power and it's not worth the money). My wife's BMW Mini is like this. Or it's optimised for 98, in which case it will have to retard the ignition a lot using 95 and quite a bit of power and economy is lost (or gained when using 98 depending on how you look at it).

[john_p]

pilchardthecat said:

It's about 7p/l (5-6%) more expensive, but i get maybe an extra 20 miles out of a 50l tank (which is about 7%) so they both cost the same, pretty much

My car is happy on 95, but you can notice the difference in power delivery between 5k and 8k rpm (s54b32 engine)

That engine is DESIGNED to run on 97/98 ron

Using 95 is possible, but with reduced power and efficiency. I'm pretty sure it says that in the manual. You're not getting 'extra' miles, you're getting less when you use 95.

[Matt_N]

swamp said:

My car's handbook says 98 RON, but I normally use 97 RON because that is all you can get most places. In fact I've never seen 98 RON, only 99 in Tesco.

Shell V Power is 99RON.

[pilchardthecat]

john_p said:

pilchardthecat said:

It's about 7p/l (5-6%) more expensive, but i get maybe an extra 20 miles out of a 50l tank (which is about 7%) so they both cost the same, pretty much

My car is happy on 95, but you can notice the difference in power delivery between 5k and 8k rpm (s54b32 engine)

That engine is DESIGNED to run on 97/98 ron

Using 95 is possible, but with reduced power and efficiency. I'm pretty sure it says that in the manual. You're not getting 'extra' miles, you're getting less when you use 95.

That sounds like you're saying exactly the same thing as me in a slightly different way.

Cost wise, there is very little in it... that was my point.

[funkyrobot]

pilchardthecat said:

john_p said:

pilchardthecat said:

It's about 7p/l (5-6%) more expensive, but i get maybe an extra 20 miles out of a 50l tank (which is about 7%) so they both cost the same, pretty much

My car is happy on 95, but you can notice the difference in power delivery between 5k and 8k rpm (s54b32 engine)

That engine is DESIGNED to run on 97/98 ron

Using 95 is possible, but with reduced power and efficiency. I'm pretty sure it says that in the manual. You're not getting 'extra' miles, you're getting less when you use 95.

That sounds like you're saying exactly the same thing as me in a slightly different way.

Cost wise, there is very little in it... that was my point.

Sorry to sound daft, but do I need to do anything else other than look in the manual to find out my engine type? I've checked the book before to find out the engine for the oil type, but can't remember it off the top of my head.

Thanks.