Premium fuels tested, results suggest no improment over 'normal' fuels

[schmunk]

What that old 1.1? It was an old N reg 106, surely the engine changed by the time the 206 was released?

TU1, introduced in 1987 and still in use on the Citroen C2 and C3.

[Funkstar]

There's a theory at the moment on the 1.4 16v (I think) VAG range engines. People are using "normal" fuels without realising the engine is designed to run on "super" fuels and as a result some components are showing signs of failure.

The 1.4 with a supercharger and a turbocharger (for performance right through the rev range) is designed for higher octane fuels. This was highlighted in the couple of reviews i read of it.

[Gumby]

Quite an interesting read!

I did think there would be a lot of difference though, maybe it's just marketing hype that justifies the prices...

[Workaholic]

I thought that the superfuels weren't supposed to last longer (miles per gallon wise) but actually made your engines etc not requre a regular repair etc..

[mycarsavw]

The 1.4 with a supercharger and a turbocharger (for performance right through the rev range) is designed for higher octane fuels. This was highlighted in the couple of reviews i read of it.

Yup, but that's the 1.4 TSI engine.

The issue I'm on about is on the 1.4 16v from 2000ish onwards.

I'll get the facts when I get home.

[Lowe]

running a normal engine with higher octane fuel can damage it (surely higher octane fuel = a bigger bang = higher compression?).

No.

Higher RON != bigger bang.

RON refers to the fuels susceptibility to detonation - that is, ignition due to compression. It has nothing to do with the amount of energy (calorific value) or the size of the resultant bang.

A fuel that has a higher RON rating will withstand more compression before going bang on its own. This is why higher rated fuels are used in performance cars that use forced induction (turbo/supercharger) or high compression engines. Using it in a 'normal' engine makes no difference at all.

[99Flake]

TU1, introduced in 1987 and still in use on the Citroen C2 and C3.

Wow that is a long running engine! Thanks for the info!

[staffsMike]

What you need to remember is that european cars are designed and their engines are mapped to run on 95 RON (normal) unleaded. So a lot of them won't see any gain.

If you have a car such as mine that is Japanese then you often need to use 98+ RON petrol as these engines were designed to run on japans standard octane fuel which is 100 RON. (98 RON is recommended in my car)

I used to use the "good stuff" in my old metro and there was a noticable amount of torque increase in higher gears (getting up steep hills etc..) so it has its uses and is deffinatly not a waste of time if you do your own little tests and it pays off..

I worked for a company heavily involved in this sort of thing for the last year or so, and it's clear when you see their tests that there are many advantages to higher octane fuels.

[Lowe]

But only if your car is properly mapped to use it...

[staffsMike]

But only if your car is properly mapped to use it...

Indeed, I should have said that

[dave87]

Some cars - Porsches, higher end BMWs, etc, recommend that you run 98 RON, and as such, will alter the ignition if you don't. IE they can use both, but are designed for the higher octane. At least that's what the dealer & manual for Porsche say...

Volvo however (D5 185bhp) gets a fair few miles more to a tank through running premium (varies by journey type, but we have noticed an increase). It also seems to pick up quicker, but that may just be driving style. (The volvo ecu will remap itself based on the fuels used afaik)

[malfunction]

No.

Higher RON != bigger bang.

RON refers to the fuels susceptibility to detonation - that is, ignition due to compression. It has nothing to do with the amount of energy (calorific value) or the size of the resultant bang.

A fuel that has a higher RON rating will withstand more compression before going bang on its own. This is why higher rated fuels are used in performance cars that use forced induction (turbo/supercharger) or high compression engines. Using it in a 'normal' engine makes no difference at all.

Ta for the decent explanation - which I do understand. Now I'm not feeling so lazy there's a much longer explanation on wiki:

http://en.wikipedia.org/wiki/Octane_rating

Edit: so the speficic energy of each fuel would be nice to know, as well as the RON

[badass]

Lower octane shouldn't cause any ill effect given that modern cars don't pink.

Not true. They do pink but with most, when they detect it the ECU automatically backs off the ignition causing power to drop.

[mycarsavw]

Yup, but that's the 1.4 TSI engine.

The issue I'm on about is on the 1.4 16v from 2000ish onwards.

I'll get the facts when I get home.

Right, I'll paraphrase from the article;

More and more 1.4 & 1.6 16v VAG cars are coming in with burnt-out exhaust valves. Certain versions of these cars require the use of 98RON but most owners aren't aware and continue to use 95RON

...

VW say it's ok but include a proviso - "in exceptional circumstances min. 95RON; however, with reduced performance"

...

We (Crasher works for C & R Enterprises - a big name in VW tuning/parts) think the prolonged use of 95RON is at least contributing to the problems.

He then goes on to list a few engines, which, if anyone cares I can include.

[Howard]

Why would they do such a thing on bog standard cars like that? Hardly anyone who isn't car savvy is going to give a toss about putting premium fuel in surely

[Zak33]

OK, lets sort some tech stuff now:

As Lowe says, the higher the octane rating (RON) the more potential bang is avalable IF the engine allows the compression to go high enough prior to the spark plug firing.

A car designed for lower octane rating fuels, will be fine and dandy on higher octane fuels. It just wont go any faster.

If a car's got cylinder by cylinder knock sensing, it will be permanently monitoring the ignition and readjusting to gain any extra power, and changing that spark timing.

However...a car designed to run on higher octane fuel, that doesn't re-adjust, and that is run on lower octane fuel WILL GET POORLY VERY QUICKLY.

Pinking is when the fuel detonates itself, under the sheer pressure of the piston's compression, before the spark plug gets a chance to do it. This is bad. It WILL cause overheating, and is in serious danger of burning out the edges of the valves, killing compression completely. It won't take long. Anyone with an old leaded car, that ran it on unleaded low octane knows that. Forget the lack of lead potentially not prtecting the valve seats......the pinking kills them long before that. It's why people had to have ignitions readjusted when unleaded came in. The lead additive then just assists in "padding" the valves seats on old cars.

When an engine is at higher revs, weirdly, it is normally better and less susceptible to pinking....pinking happens at lower revs, under heavy loads (going up hills and pulling away) and that's because the pistons are travelling much slower and therefore the compression gets a long, slow chance to bang the fuel prior to any input from the spark plug. At higher revs, it's so bloody fast, that the difference between the compression starting it off and the spark plug going at it, is miniscule.

Don't forget....diesels pink by their very nature. It's OW the diesel fuuel is set off to go bang,.,,,aint no spark plug....just compression. The noise of a diesel IS pinking. It's the "loose marble in my engine" noise.