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[GastronomicKleptomaniac]

 How do

 With my new toy arriving on Thursday, I'm just curious as to whether it's worth the extra to put 97RON fuel in? I'm going to start with some Redex in the first tank I put in, but is it worth the extra few quid/ tank to put Super instead of Premium in?

Regards
Pete

[Kevin Wood]

Some say it's worth it, and gives better fuel consumption and more power, some say it isn't :-/

The Omega petrol engines are controlled by knock sensors so in theory they can retard ignition timing to compensate for poor fuel (and by the same token, they allow it to advance, to a point, on higer octane fuel).

To reap a huge benefit from Super Unleaded you need an engine that's either in a fairly high state of tune or is Turbocharged, Supercharged, etc. The Omega engines don't fall into this category, although the 3.0 V6 does have a relatively high compression ratio (10.7:1).

The best answer is that it won't hurt to try it so do so and see if you think it's worth the extra.

Kevin

[Entwood]

Totally subjective unproven opinion ...

For long distances, especially towing, I use Shell SuperV, appears to give me more power and better fuel consumption.

For short distances/commuting etc etc normal Shell unleaded as I seem to spend as much time stationary as I do driving.

Supermarket fuel seems to give poor consumption and less grunt, even the higher octane stuff, and once in France when all I could get was some very poor quality cheap stuff ( back of beyond little village + empty tank light on !!) I had intermittent emission type warnings for 2 days (code 44). They went once I refilled with 1/2 a tank of decent stuff.

I have no proof of this .. just how it seems to be for me ..

[justme]

Save your money redex and most other additives ranging in price from £5 < £20 will reduce your power and performance by approx 2%.
Tests carried out by an engine test centre in Oxford for 5th Gear.
You will definately get better performance and mpg if you do not use supermarket fuel  + 30% Ethenol.

[Phil B]

I just filled up today and as I was grabbing for the normal unleaded nozzle I did a quick sum.
Turns out it only cost an extra £2 for a full tank of super rather than normal 95ron, so I chose super as an experiment.

Well, so far the drive home seemed much smoother and the car also seemed a little 'readier'. I will confirm this with the drive to work tomorrow but the way it purred and idled by the time I got home I think it's made a noticeable difference.

I used to put super in my 2.0 24v V6 Mazda Xedos6 (what a great car, if only it were Rwd) as it made a huge difference, and at not much more cost.

They are what they eat!

[GastronomicKleptomaniac]

Cheers guys, much appreciated. I've always wondered if it's just psychological, like you think it's smoother simply because you've put the 98RON in - but my Almera even seems just a little less... swift... running on 95RON.

[magnul]

Well, if the engine via the knock sensor could completely adapt to high octane fuel, what would be the benefit of a chip? AFAIK, remapping a NA engine would basically involve increasing the ignition advance to match a higher octane fuel.

[Kevin Wood]

Well, if the engine via the knock sensor could completely adapt to high octane fuel, what would be the benefit of a chip? AFAIK, remapping a NA engine would basically involve increasing the ignition advance to match a higher octane fuel.

This is a good point. Even if the knock sensor is not retarding it the manufacturer's ignition timing value is going to be on the "safe" side, and there will be other concerns such as emissions which cause a manufacturer to compromise on power output when tuning an engine.

Having said that, most 4 valve per cylinder engines do not need high levels of ignition advance to produce best power, and so don't need a high octane fuel to avoid knock unless running a lot of compression or boost.

The holy grail is ION sensing, which allows an engine management system to sense the pressure in the cylinder during firing and adjust the ignition timing in a closed loop fashion to give best power. Not available on an Omega but I believe a few Saab engines have it.

Kevin

[The Cambelt Kid]

Very interesting thread...  

I understand that Scooby Doo's don't run too well on anything less that 98 ron.  I take it that they can't retard the timing enough to run on low octane fuel.  

Fancy being forced to run on hi-octane fuel!!!  I don't suppose anyone will convert one to run on lpg then?

[Kevin Wood]

Very interesting thread...  

I understand that Scooby Doo's don't run too well on anything less that 98 ron.  I take it that they can't retard the timing enough to run on low octane fuel.  

Fancy being forced to run on hi-octane fuel!!!  I don't suppose anyone will convert one to run on lpg then?

Scoobies are turbocharged so they are more prone to knocking because the fuel/air mix is forced into the cylinders under pressure, and at higher temperature. The mixture reaches higher pressures and temperatures in the cylinders before combustion starts and this can cause a low octane fuel to ignite prematurely or too violently when triggered by the plug. In either case the fuel burns much too rapidly (detonation) and it is this uncontrolled burning that causes shock and extremes of temperature and pressure in the engine, causing damage if it is unchecked.

A knock sensor is there to detect the shock waves this type of burning generates. If it happens in a modern turbocharged engine it will retard the ignition and, in addition, reduce the boost pressure so you get a more serious performance loss. It'll probably save the engine but why drive a scooby if it's badly down on power?

A mate of mine drove a cossie turbo engined car across the US a couple of years ago. It didn't have knock sensors and he got a dodgy batch of fuel. He didn't notice the knocking because the car is loud in any case, and the damage ate away at the aluminium cylinder head around where the head gasket fire rings sit until he lost compression, rendering the head scrap. Brave attempts were made to fix it (i have photos of him lapping the valves in a hotel room!) but to no avail  

LPG is actually effectively a higher octane fuel than super unleaded so you'd probably be OK on that. Might be a complex conversion though.

Kevin