Shell 'Optimax'

Thanks, Tony.

I have some further testbed experience of Shell Optimax compared to my last post of just over a year ago on this topic. I work for an engineering consultancy and my last three years have been spent leading the design and development of new high powered production engine that will be on sale next year.

1. Like I said in my last post, on modern engines with adaptive knock (detonation) control systems that are tuned at higher octanes, the benefits of are clear. However, after completing the development work on this engine I can add that even if the calibration is fixed at a lower octane (say 95RON), Shell Optimax at 98RON may give an improvement in the suppression of transient knock and especially so in warmer weather (>25degC). What I mean is that when you put yor foot down quickly, if there appearance of knock in one or more cylinders, the control system will then act and reduce the ignition advance (as quickly as by the next cycle) on the offending cylinders. This is usually more apparent to the customer during warmer weather unless a manufacturer has not done his transient fuelling work to sufficient detail (some don't), in which case this will happen at cooler temperatures aswell. A higher octane rating can suppress this knock and maintain performance levels. Having said that, even standard pump-grade 95RON is nearer 97RON so only the more sensitive drivers will notice the difference at 98RON.

2. Shell Optimax does indeed have a good additive pack (I'm not saying its better than Texaco or BP, I don't know because I have not done the back-to-back test). After a very severe durability test on one of our engines specifically on this fuel, the condition of the piston crowns was cleaner than normal. We also had no fuel injector deposits which we suffered when using a known lesser-quality additive pack on the same test. I don't remember the valves looking any different.

I also tried Optimax on my own car which is calibrated at 95RON but adapts down to 91RON (a VW 2.0 engine with a well developed engine calibration). I noticed an improvement in transient response during very hot summer days. I aslo got a 3% improvement in fuel consumption compared to standard, possibly down to the suppression of hot temperature knock. There was no improvement at lower temperatures.

Hope this helps.

Rana

6 months ago I became the owner/driver of a new Audi A2 1.6 FSI. Every fill up since has been optimax, This week my local petrol station ran out so I filled up with regular. Performance in every respect was noticeably poorer within a few miles, enough to ensure future fill ups with Optimax.
Larry

Is it just Optimax,or Shell petrol in general ?

I have not tried the Optimax stuff,just the normal unleaded,but what i have noticed is that if I run my car on Shell petrol,it seems to run better & have a bit more "get up and go" But if I run it on Texaco or the stuff that Tesco,Asda etc sell. For some reason,it seems somewhat "flat" by comparison.

I just happened to comment about the Shell/Texaco thing when round at my parents & my father,(who has a diesel) uses Shell for the same reasons .

(can't really comment on any of the others,such as B.P. as my normal driving habits seem to dictate Shell / Texaco)

Puzzled

Chris

(Car = BMW E39 M52 engine)

quote:

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Originally posted by Chris Brandon:

I have not tried the Optimax stuff,just the normal unleaded

(Car = BMW E39 M52 engine)

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Chris, you should have a close read of your owner's manual. BMW recommends running their cars on Optimax (or equivalent spec).

John,

Just dug the manual out......
Quote....

Spark-ignition engine with catalytic converter

The engine should be run exclusively on unleaded fuel.Since the engines have a knock control function,they can run on different grades of fuel.

Minimum fuel grade: Regular-grade unleaded fuel(octane number 91,Research method).

The rated performance and fuel consumption valuesare acheived with :

Premium-grade unleaded fuel (octane number 95,Research method)

This fuel is also known as: DIN EN 228 or Euro-Super.

For higher performance and lower fuel consumption,it is also possible to use

Super Plus/premium fuel ( octane number 98,research method).

So,it "should" in theory run on most unleaded. But curiosity is something I was born with in excess,so might just have to try Optimax for a couple of months and see how I get on.

But,whichever this pans out,my car just seems somehow happier on Shell as opposed to Texaco

Time to get some breakfast

Regards

Chris

quote:

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Originally posted by Chris Brandon:
So,it "should" in theory run on most unleaded. But curiosity is something I was born with in excess,so might just have to try Optimax for a couple of months and see how I get on.

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Interesting the different wording for different series with what I thought were the same engines. My 3 series manual says "Super Plus 98 RON - run the engine on this fuel grade by preference, in order to achieve rate performance and fuel consumption."

I think it is really just semantics. The tune itself will probably be identical, but the wording reflects the availability of fuel grades at the time of release and in specific world markets - ie initially only 95RON unleaded gasoline was widely available, now 98RON and above is commonplace.

If the handbook said use 98RON for optimum performance, but you could only find 95RON, then you might be concerned.

Hope you enjoyed your breakfast ?

Regards,

Brian

Brian..."Hope you enjoyed your breakfast" ?

Certainly did ! ... So much so in-fact that I had to visit the "Big Fat Xmas B*stard" thread

Regards

Chris