Welshman

See the attached article from today's Sunday Times:


The Sunday Times



October 03, 2004

Fuel: The wonder fuels that don't deliver
The ads claim they are wonder fuels but our test was less than impressive. Dave Pollard reports



It is, according to Shell, petrol

Beardie

One of the knowledgeable guys will be around shortly but my 2p.

I try and run Optimax for 3 reasons.
1. The instruction from Honda is 98RON or 95 for short periods.
2. I like the idea of less engine deposits
3. It makes me feel like I'm looking after my baby

I seem to recall an article somewhere on an independent test that ran 2 engines on a test bed for 100,000 miles. One on Opti the other on regular unleaded.
They were then dismantled and inspected. The Opti engine had practically no deposits.

Also found out what Optimax can also be used for. Look here.

euan

I certainly do notice a difference using SUL and UL, but it's not hugely significant. I think the extent it affects the perfomance of the car must depend on the car and it's ECU - I imagine performance cars are designed to run on higher octance fuel, and as such it does make an appreciable difference.

Personally, the sharpness I get from Optimax et al (and the need to keep this fussy engine as smooth running as possible) means I use SUL whenever I can.

tim_d

My old Saab was a lot better on optimax than normal UL. It was especially noticable when towing, but was always more economical on it. To the point that there was no difference in overall cost - more miles per gallon from the more expensive fuel.
Haven't run the Honda on normal UL so have no idea what the difference is, but it's not that much more expensive here anyway (in fact optimax on one side of the A11 is the same price as regular UL on the other!!) and the alleged benefits in terms of engine cleaning make it worth it for peace of mind, IMO.

Shipley

I saw an independant test where they stripped two engines after 10k miles being run on Optimax and normal unleaded.

There was a huge difference in the state of the engines.

Equally, I can tell what fuel I have in by how the car runs.

It works for me, and that's therefore all the car gets. Doesn't exactly cost a huge amount either.

fluffyninja

Wrong, wrong, wrong

Fuel doesn't explode in the chamber it burns. When it explodes it's called knock and it causes damage to the engine if allowed to continue knocking.

Knock is caused by a combination of high pressure and temperature in the combustion chamber. To get power out of your car you want the fuel to be burning at it's fastest as the piston starts it's downward stroke and so you light it before the piton reaches the top so the flame front has time to propogate. The earlier you light it the higher the pressures and temperatures in the combustion chamber and the more likely you are to get knock.

A higher octane number means less likely to knock hence if the engine ECU is programmed to take advantage of it it will give a performance advantage by being able to advance the ignition timing further before knock occurs. If however the vehicle is a complete shed like the C-max you probably won't get a noticeable difference.

Shiskine

My two penneth ...

Several years ago, when I was running the Chimaera and was considerably more hard up than I am now, I stopped running it on Super Unleaded because, at 14 mpg, I simply couldn't afford the premium. Most of the TVR forums reckoned this would do no significant harm to the engine, despite the manufacturer's recommendation to use 98 RON.

I would ocassionally "treat" the car to a dose of SUL, but if I'm really honest, I don't think I could tell the difference. I would agree with eibutler, that filling up with SUL simply makes you feel better about the car.

I have to confess that since getting the S in mid July, I have exclusively filled up with Optimax and the odd does of Ultimate (because I'm worth it ...), but when on Arran for my hols, I had to fill up with 95 RON cos there's no SUL on the island. Again, I'd struggle to tell you it affected performance.

Even now, there are days when the car doesn't feel quite as pokey as the last time I gave it a blast. But this sort of subjective assessment is as likely to be influenced by such technical factors as how hung over you are from the night before and just how "up for a blast" you are at that particular moment. The S is still a novelty and I'll go out for a drive, not because I'm really in the mood to, but because I just want fondle my new toy. Sometimes on these occasions, it doesn't feel as quick but I'm sure it's all in my head

Shiskine

Bassoctopus

My Scooby ran like a bag of nails on 95, but was great on 98

I run the S on Esso SUL, about 4p a litre less than Optimax and about 6p less than Ultimate but still 97RON

fluffyninja

We're gonna get back ino the whole MON/RON/PON discussion again

Whether you get any benefit from using a 98RON fuel is determined by if the ECU map is set to take advantage of it

mikey k

IIRC the ECU has to learn the RON and the driving style. Quickest way to do it is reset it once you have filled up with a different fuel! So if you have run SUL @ 95 RON it will take a while for it to "recognise" Optimax @ 98 RON. I mix Optimax, Ultima and SUL depending on which station comes first and have noticed no difference because I do not reset the ECU each time I change brand!

I like the idea of the additives to prolong engine life, sceptical about the power increase!