Petrol - 95, 97 or Optimax

[keithskip]

I use 97 octane super unleaded - which is around 8p a litre more than ordinary unleaded - unless I'm running short and there's no super around. Am I damaging the Griff with ordinary unleaded - or am I paying 4 quid for nothing every time I fill up with super? And what is Shell Optimax?

Appreciate your help - but pse don't make it too technical!

[spnracing]

You'll get varying views on here.

Mine are;

Optimax is 98.4 octane. Unless you advance the timing to make use of this (and always use Optimax) you won't see any advantage. The only exception to this would be if you left the car standing for a long time and the petrol went off, so maybe Optimax would last longer.

The car is probably tuned to run on 97/98 Super - so normally you should use that.

The car could easily be slightly tuned to run on 95. You will never notice the difference in performance and - like you say - save £4 a fill up.

To be honest my 400 Chimaera ran on 95 occasionally and it NEVER pinked - so you'd probably get away without the detune.

The difference in performance between 95 and 98.4 octane petrol is probably less than other steps you could take such as;

Removing the spare wheel
Not always running a spare tank
Making sure the plugs/oil are clean (i.e. regular servicing) etc.

Another point - I have been told in the past that because Super is used less frequently in petrol stations, it is refilled less and is therefore always older than the 95 pump petrol. Thus its possible that it has gone off to the point that it is a lower octane anyway.

[Podie]

Evo did a big test on OptiMax.. results varied.

Ted - perhaps it's time for an FAQ section?

(if there is already one that I haven't noticed - head in the sand me! - think we need an OptiMax bit!)

[shpub]

There is an unleaded FAQ on my website which covers what you need to do:

In summary:

All Griffs and Chimaeras like Super or better cos of the higher octane. This includes Optimax.
They shouldn't be run on U/L except as an emergency as they may pink or predetonate both of which can damage engines given time.
Some cars will because of variations in engine build run quite happily on U/L. Most won't and need a timing change except for those that are really finicky and need a rechip!

So basically if your engine is standard and you don't want to risk damaging your engine use Super or Optimax. If you want to save money get the car adjusted so that it doesn't pink/pre-detonate.

It is also in the bible.

Steve
www.tvrbooks.co.uk

PS My Griff has been chipped and runs on U/L. The 520 needs as much Octane as it can get and uses Super or Optimax or UL with octane boost.

>> Edited by shpub on Friday 20th September 12:37

[shpub]

There is an unleaded FAQ on my website which covers what you need to do:

In summary:

All Griffs and Chimaeras like Super or better cos of the higher octane. This includes Optimax.
They shouldn't be run on U/L except as an emergency as they may pink or predetonate both of which can damage engines given time.
Some cars will because of variations in engine build run quite happily on U/L. Most won't and need a timing change except for those that are really finicky and need a rechip!

So basically if your engine is standard and you don't want to risk damaging your engine use Super or Optimax. If you want to save money get the car adjusted so that it doesn't pink/pre-detonate.

It is also in the bible.

Steve

PS My Griff has been chipped and runs on U/L. The 520 needs as much Octane as it can get and uses Super or Optimax or UL with octane boost.

[Podie]

quote:
PS My Griff has been chipped and runs on U/L. The 520 needs as much Octane as it can get and uses Super or Optimax or UL with octane boost.

Sounds expensive. Think I read somewhere that you can buy 100 octance fuel in Japan...?

[Ballistic Banana]

Not having many Optimax pumps in the area i run mine on 97 and so far no problems.
Have heard of some motors starting to 'pink' and some performance issues ie like a fuelstarvation stutering sort of thing.
I think it might be a bit of trial or error but i wouldnt use 95 as theres a chance of excessive pinking.

I believe theres something in the Bible about it,will look up later if nothing else is brought up

BB

adited due the 'Master' getting in there first,

Hopefully thats sorted now.

>> Edited by Ballistic Banana on Friday 20th September 12:41

[cockers]

Just to chuck in my view, I have never noticed any performance difference no matter what fuel I use (4.0 Chimaera).

However, Optimax smooths out low revs running like you wouldn't believe. I was starting to think it might just be pyscohological, but for various reasons I haven't been able to get Optimax for the last two fill-ups and it's kangarooing like a good 'un in the traffic jam that is my daily commute. Will be putting Optimax back in ASAP!!!

[shpub]

quote:
Sounds expensive. Think I read somewhere that you can buy 100 octance fuel in Japan...?

Genuine 4star is around 100 octane and is easier to get than going to Japan. It is about £1.10 a litre though so I tend not to use it. especailly as I only get about 2-3 miles a litre unless I am really thrashing it....

Steve

PS you can't use 4* if you have a cat!

[M@H]

quote:

quote:
Sounds expensive. Think I read somewhere that you can buy 100 octance fuel in Japan...?

Genuine 4star is around 100 octane and is easier to get than going to Japan. It is about £1.10 a litre though so I tend not to use it. especailly as I only get about 2-3 miles a litre unless I am really thrashing it....

Steve

PS you can't use 4* if you have a cat!

I thought that genuine 4star was 98, and 5star (long since departed) was 100... and I going mad steve

[spnracing]

You can use Millers VSP added to Optimax - apparently that raises the octane of an average sized tank to about 100. The bottle of Millers will cost you up to a fiver though. I run it in the Golf.

[steve-p]

Four star leaded was only 97 RON, Super Unleaded 98 RON. Five star leaded was 100 RON but that has been unavailable for many years.

If the car is not set up for a higher octane rating, or cannot compensate itself by automatically adjusting the ignition timing to the optimal point for the fuel, there is no benefit whatsoever in using octane boosters or higher octane petrol. Five star petrol in an early mini set up for two star did not make any difference whatsoever to economy or performance.

[M@H]

quote:
If the car is not set up for a higher octane rating, or cannot compensate itself by automatically adjusting the ignition timing to the optimal point for the fuel, there is no benefit whatsoever in using octane boosters or higher octane petrol. Five star petrol in an early mini set up for two star did not make any difference whatsoever to economy or performance.

Agreed.. I can honestly say that my beetle 1200 designed for 3 star really didn't go like brown stuff off a gardeing tool with 4 star in it... I reckon you need a tiger in your tank for that

[shpub]

quote:
I thought that genuine 4star was 98, and 5star (long since departed) was 100... and I going mad steve

I can't comment on your mental health but yes you were right before 4* went from general circulation. The 4* that is still available is nearer 100 octane from reports that I have. John Eales who built the 520 engine reckons itr is great for pre-cat cars but he doesn't pay my petrol bills.

Steve

[keithskip]

Thanks for advice Guys. (Thinks...Bible...!)

[joust]

quote:
Optimax is 98.4 octane. Unless you advance the timing to make use of this (and always use Optimax) you won't see any advantage.

Autocar (or was it AutoExpress) did a test of "before and after" using Optimax. On every car excpet the BMW they tested on it, the valves and seats were much cleaner after a few hundred miles on Optimax than normal petrol.

Also - all the users said they "felt" a difference.

Any car with a nock sensor will automatically advance the ignition to take advantage of the higher octane, and the detergents in the petrol may well help in the longer term..

Not sure if TVR's have knock sensors though - or if they are set to a fixed octane rating - and if so what that is.

quote:
Another point - I have been told in the past that because Super is used less frequently in petrol stations, it is refilled less and is therefore always older than the 95 pump petrol. Thus its possible that it has gone off to the point that it is a lower octane anyway.

Err - not sure what you mean by "go off" - could you expand????

Edited to get quoting right....
J

>> Edited by joust on Friday 20th September 17:26

[joust]

quote:
Sounds expensive. Think I read somewhere that you can buy 100 octance fuel in Japan...?

See www.vtr.org/maintain/gasoline-octane.html for some wacky ideas on increasing octane. STP and others seem to do a more "mainstream" version which will get it over 100..

J

[scruff400]

Hordinary hooning, you'd probably be OK on 95 (regular)
Thrashin the harse off it - 98RON to stop it pinking...

I reckon (specially now that I've run out of money.)

Edited to remove the word Giblet.

>> Edited by scruff400 on Friday 20th September 18:29

[steve-p]

quote:Any car with a nock sensor will automatically advance the ignition to take advantage of the higher octane

Not really. At least, usually only as far as the original fuel grade intended for the car, which will be either 97 RON super or 95 RON premium in any car built in the last ten years. The knock sensor is there to prevent engine damage from pre-ignition caused by fuel below the octane rating intended, for example with the 89 RON rubbish on sale in Eastern Europe, and US grades that are less than our ordinary unleaded. It does not automatically follow that there will be any advantage from fuel that exceeds the intended grade.

[joust]

quote:
Not really. At least, usually only as far as the original fuel grade intended for the car, which will be either 97 RON super or 95 RON premium in any car built in the last ten years. The knock sensor is there to prevent engine damage from pre-ignition caused by fuel below the octane rating intended, for example with the 89 RON rubbish on sale in Eastern Europe, and US grades that are less than our ordinary unleaded. It does not automatically follow that there will be any advantage from fuel that exceeds the intended grade.

That ain't what my BMW X5 manual says..... it clearly states that the knock sensor is there to improve performance if you wish to move up to 98 (using words such as "drivers that wish to gain above normal performance" and such like) along with the S mode on the auto slushbox. However, it clearly says that it's designed to use 95 as normal fuel - and says on the petrol cap that it can cope with anything form 90-98.

Also www.total.co.za/External_content/products/automotive/petrol_octane.htm and a whole load of other sites if you put "petrol knock sensor" into google would have me believe different, but perhaps it's all a bit of sermantics (i.e. what's normal???)

But hey - what do I know - I'm an electrical engineer [cue lots of how many xxxxx engineers does it take to do yyyyyy]

Edited to remove a funny spelling of normal

Joust

>> Edited by joust on Saturday 21st September 00:18