Shell "Optimax" fuel....any good????

[The Pied Piper]

Anyone got any thoughts on using this new fuel in high performance engines??

 

I have a 2 ltr XE Vaulhall in my rally car, 235Bhp spec, which for the last year I have been running on Shell Super unleaded plus 1% Silkolene Pro-boost. This is because previously, I have suffered from detonation damage in the cylinder head apparently caused by running ordinary unleaded fuel (95 octane).

 

I am led to understand that the older "Super unleaded" is 97 octane as oposed to the 98 octane that it was originally supposed to be. I therefore added 1% pro-boost to bring this back up to 98 octane. During the past 12 months I have used this fuel mix and I have never had any recurrance of the overheating which was being caused by the damage to the head gasket by the severe detonation.

 

As the Shell Optimax website states that this new fuel is definately 98 octane, I have decided that I no longer need to add the Pro-boost.......or do I??? Also it's cheaper at 79.9p/Ltr as oposed to 86.9p/Ltr, + 8p/Ltr for the Pro-boost.

 

I'm shure some of you with hi-spec XE's in your 7's must have considered this, what are your thoughts/experiences???

[EFA]

Optimax will probably put your engine back to its mapped environment, but I am suprised you got detonation as most if not all competition engines are set up to run slightly rich at the top end.

 

Unless you remap on Optimax or have a closed loop injection/ignition system (which you dont't otherwise you would not have suffered detonation in the first place) you will see no benefit.

 

On certain road cars with a closed loop injection/ignition system you will see an improvement - probably in smoothness at the top end.

 

My Fiat 20v Turbo definately runs better on it.

 

Fat Arn

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[The Pied Piper]

Arnie,

 

Thanks for your comments... I don't run a closed loop system, it's a DTA unit on throttle bodies and it is biased towards the rich end.

 

I assumed the detonation last year was caused by running too much advance for the quality/octane of the fuel I was originally using (95). It was definately detonation, the symptoms were severe overheating and pressurisation of water system, no oil in water, but upon removal of head found severe pitting like sandblasting on head chamber near inlet valves which had caused the head gasket to breach between the waterway and the cylinder.Also the pistons were in a similar state between the top ring and the crown adjacent to the inlet valves.

 

This happened twice, then I built a new head, ran it on Super+ 1%boost and never had a problem since. I've made no changes to the fuel or ignition mapping.

 

What I'm asking is will the Optimax at 98Oct do the same job as the Super + the boost???

 

Regards,

 

Martin

[JKJ]

I would think that Optimax would probably bring your octane rating nearer to UL + octane boost, 95 + 3 rather than SUL + the same = 99/100. Use the latter in my Prodrive Impreza to obtain the full 250 bhp but will give this Optimax a go. Hopefully filling up will become a little bit less painfull, if it's suitable.

[Peter Carmichael]

Optimax claims a fast burn rate. This is significant.

 

The ignition advance gives the mixture time to burn and generate the pressure to acclerate the piston. If the mixture burns slowly you need more advance. If the mixture burns quickly you need less advance.

 

Typically, 95 RON unleaded has a quicker burn rate than 97/98 RON super. If you map for Super, you put more advance into the map. If Optimax really does burn faster, you might need to reduce the advance to keep the engine at minimum best timing - max power, max buffer to detonation.

 

Shell are utter bastards for saturating the market with gumph that just says the fuel is *the best* but doesn't explain why. Time for some letters to Shell, methinks, to get some technical data.

[Tony Martyr]

I noticed that Demon Tweeks have small print warning about NOT using their jerry cans to store super-unleaded fuel. This was a puzzle to me although I am aware that any fuel will deteriate.

I asked contacts at Shell specifically about Optimax in this regard and got the following reply:

There is a common misconception (which I believe to be historical) that

Super Unleaded petrols have a higher aromatic (and benzene) content than standard Unleaded fuels. High aromatic contents can be responsible for the swelling and deterioration of certain polymers, some of which may be present in the below mentioned 'jerry cans'.

As I said, this is a misconception, the specification for aromatics and benzene content of Super Unleaded is no different to that of Regular

Unleaded (42%max; 1%max), and in fact, the specification for aromatics and benzene content of Optimax is no different to that of Ultra Low Sulphur Petrol (35%max; 1%max).

For these reasons I cannot foresee any problems with using the jerry cans for Optimax (though I am pretty sure they should not be used for long term storage of any kind of fuel).

Helen Scholey

Fuels Technical Advisor

Shell UK Oil Products Ltd.

I suggest you use this source to ask other questions you may have concerning Optimax

 

[DaveK]

Tony

 

The warning re super unleaded was because we had batch of people complaining that the paint that is used in the jerry can was coming off and contaminating fuel tank.

 

We use the same jerry cans for our own race cars and just use a funnel with a filter which is comman sense any way!!

 

Re octane boosters ,the millers cvl "upper cylinder lubricant"is supposed to increase octane by 2-3 points. excellent for series where you are not supposed to use octane boosters

 

cheers

Dave