...as I said I don't know, always thought that knocking/pinking caused damage (burnt valve seats)

I'm just skeptical, as I've seen these cleaner/performance fuel marketing campaigns come and go for 35+ years. Never are they backed up with clear (graphical) evidence.

Personally the "tiger in my tank" was my favourite.

Knocking/pinking/detonation - Is when the fuel explodes before the spark plug ignites the fuel due to a very high compression in the cylinder, that is on of the reason's IIRC that turbo car engines have a low compression ratio.

If the fuel is burnt before TDC I suppose then the car will be down on power and also I would of thought stress on engine components would be alot greater due to the exploding fuel forcing the piston down where as the natural revolution of the engine forcing it up.

Ran with Optimax in the Scooby religiously and saw an increase in performance and fuel economy. BP Ultimate made it run very roughly (yes I did try 3 or 4 tankfuls ) and according to the majority on Scoobynet causes large amounts of knock in the Scooby engine. Not had a chance to properly try the BP Ultimate diesel or Shell Diesel Extra properly on the Fabia yet....

Chris

Going back to the diesel for a mo....

I've have been using Shells Diesel Extra for about 10 tankfulls or so. Car is so much improved as it runs smoother and economy is superb. And for 78.8p you can't complain. However with Tescos 5p a litre off deal I'd give them a chance and the difference is unreal! The car doesn't pull away from standing as well and doesn't do as well at low rev's / Economy has also fallen massivily. Over the last 3 Tesco tankfulls I have dropped from 54.7mpg to only 46 mpg. This is massivly dissapointing to me and I will go back to Shell on the next tankful. Might not be all just marketing hype.

OK I accept that...

Strange they don't push that on the Optimax pages. :confused:

But then its strange that they overquote their oil reserves....

Locally' date=' its competitive (about 1 or 2p dearer) with supermarket petrol.[/quote']

Hmm, are you sure you're not confusing the price with the ordinary Shell?

I've switched to 95RON since the petrol prices went silly, but a few months back Optimax was 78.9p, Shell 95 was 73.9p, and Asda's finest 72.9p.

I have to say I've noticed a drop in fuel enconomy since switching to 95RON. I think I might try a few tankfuls of Optimax again - or maybe BP Ultimate as the BP station is more convenient.

The car doesn't pull away from standing as well and doesn't do as well at low rev's / Economy has also fallen massivily. Over the last 3 Tesco tankfulls I have dropped from 54.7mpg to only 46 mpg. This is massivly dissapointing to me and I will go back to Shell on the next tankful. Might not be all just marketing hype.

Economy on Tesco fuel sounds about right and I average around 50mpg on a tank with a mix of country lanes and motorway driving - what can I say? I'm a sucker for Clubcard points Still, hopefully Shell Diesel Extra will be making an appearance locally soon (it's not like Southampton isn't a major port ) so I can try it properly

Chris

The Renault Clio 172 and all models afterwards have knock sensors, they basically advance the timing until a knock is detected then they retard back slighty to get the best performance for the variable (Petrol/Air temp etc) presented to the car IIRC.

Pretty sure most sports cars do this - I know the Scooby does - doesn't really make sense not to

Chris

I am starting to think maybe there will be an increase in MPG if your engine has a knock sensor that allows the ECU to retard and advance the timing.

My theory behind this is the engine will produce more power if a high octain is used.

For example at the same throttle postion and all other parameters being equal like the same road surface / ambient temp / car weight etc a car running 98 RON will produce more power than a 95 Ron car which means the 98 RON car will be travelling faster thus covering a larger distance for the same amount of fuel used.

Right now that's cleared up I am gonna crack the secret of life

Chris yes mate I believe it would be stupid not to fit any car from now on without a knock sensor due to the different flavours of fuel available, the only reason I can think of not to fit a knock sensor is to keep building/parts cost down.

Hmm, are you sure you're not confusing the price with the ordinary Shell?

Yes I was , (now edited) it is 6p dearer.

Am starting to get drawn in to the hype....:squint: I wonder if....

Would you think that running in a new car on Optimax would see any benefit? (I'm thinking in terms of lubricant to the valves etc)

Yes I was ' date=' (now edited) it is 6p dearer.

Am starting to get drawn in to the hype....:squint: I wonder if....

Would you think that running in a new car on Optimax would see any benefit? (I'm thinking in terms of lubricant to the valves etc)[/quote']

The best stuff for lubricating the valves was the old Leaded petrol and I believe this had a RON value of 99 as well ! Valves will be lubricated buy the oil at the essential parts, all the cars that run unleaded have hardened valves stems so I think it may be hype TBH.

I don't know if this has already been touched on (I read most of this thread yesterday and can't remember) but aren't Optimax and Ultimate just rebranded Super Unleaded?

Chris yes mate I believe it would be stupid not to fit any car from now on without a knock sensor due to the different flavours of fuel available, the only reason I can think of not to fit a knock sensor is to keep building/parts cost down.

Even my old MG Montego circa 1990 had a knock sensor...

I don't know if this has already been touched on (I read most of this thread yesterday and can't remember) but aren't Optimax and Ultimate just rebranded Super Unleaded?

Interestingly, although Ultimate is labelled as BS7800 (the standard for Super Unleaded), Optimax (according to Shell's own website) is only tested against BS EN 228 (Unleaded).

I suspect (without any real proof) that Ultimate comes out of the refinery at 97RON, while Optimax is 95RON with a bucketload of octane booster. This could explain the perceived variability of Optimax.

Even my old MG Montego circa 1990 had a knock sensor...

But wasn't that to detect when a wheel was about to fall off?

:snail:

Even my old MG Montego circa 1990 had a knock sensor...

FastVeRSion was it fuel injected then ?

It was indeed. I had a Montego Turbo as well, but that had a carb... Think i'm remembering correctly, it was a long time ago!

Montegos, they were great fun. The MG Turbo I had was so prone to rusting, I had to respray the bottom half of it twice - it was white, and the rust stains just kept coming through. Actually, it was amazingly quick, but the chassis was completely overwhelmed by the motor, I have never felt torque steer like it before or since :eek:

My Legacy Turbo runs much better with Optimax. I use Octane Booster as well.