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I've looked at various post on here, but can anyone tell me roughly what Bhp increase can be had by swapping from Unleaded to Super Unleaded?

Also, what about the difference after adding octane boosters?

I use normal unleaded at the moment, but I thought I'd ask here before wasting more money

Thanks
Skiddins
 

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No idea, but peak horsepower is probably not where you'd see the difference. If the octane is too low (and standard unleaded at 95 RON generally is for the B234R engine), then it is peak boost and hence peak torque that suffers. By the time you get to about 5500 RPM, where peak power is, you're way down from peak torque and more octane won't help.

You should feel a stronger "pull", although the difference is likely to be reduced in this cooler weather when even 95 RON isn't so likely to cause knock.

Anyway, peak horsepower isn't what these cars are all about. It is the huge mountain of torque that makes mincemeat of many cars that are more powerful on paper. Anything you can do to increase that torque further just has to be done
 

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Oh, and octane boosters - I've read that none of the products on the market actually increases the octane of the fuel. Rather, they tend to change the characteristics of the knock such that the knock sensing is less likely to detect it. Whether this also means it is less damaging to pistons and valves, I really don't know. I think that if oil companies could raise the octane with stuff that you and I can handle fairly safely, they wouldn't bother with the ultra-hazardous additives that they do use.

Only hearsay and supposition, though. I'll stick to Optimax, though, which at least around here, is cheaper than other Super Unleadeds.
 

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I always use Shell Optimax in my 9000 Aero as it feels like it pulls better, idles smoother, and generally "wants to go" all of the time - and I often like to make use of this

I know Optimax is more expensive, but then again you will get slightly more miles to the gallon.

Having said this I tried Optimax in my wifes 9000 2.3 LPT auto, and hand on heart I could'nt see much difference, more because of the way one tends to drive the car i.e. "quickly" rather than "going for it".

Why not try a couple of tanks of super/optimax then if you can't tell the difference save your money.
 

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I have always used Superunleaded in my 2.3 turbo - never noticed more power but have noticed smoother idling and better fuel economy.

Also - a warning that i once put some redex petrol treatment in the tank ( supposedly cleans injectors- helps combustion) and it made the car run like a dog - looked at spark plugs and they had turned orange- I had not even put a full bottle in the tank either. So avoid !
 

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Just a couple of comments to avoid any confusion amongst our European or American brethren.

What we in the UK tend to refer to as standard unleaded is actually Eurosuper (95 Research Octane Number), and the higher octane stuff is Superplus.

In most of continental Europe you will find:

Normal: 91 RON
Eurosuper: 95 RON
Superplus: 98 RON

In the UK we have never had 91 RON unleaded fuel. The old two star leaded fuel was 90 RON.
You might also have noticed recently that those garages (not Shell) that still sell high octane fuel have reduced it from 98 to 97 RON to match the old leaded 4 star. Shell's Optimax was originally marketed as being "at least" 99 RON. I have not noticed that it has been lowered with the other high octane fuels.

Given that, at least near my house, Optimax is cheaper that other companies' 97 octane fuels, I use Optimax when convenient, and 95 RON when no Optimax is to be found.

I have tried the octane booster that Trent Saab supply (Proboost or a similar name), with a tank full of Optimax, and not noticed much difference. Octane boosters tend to be a pretty expensive alternative to Optimax, or even 97 RON fuel, and one has to question whether high octane fuel is necessary, especially in the cooler periods of the year, and for those of us without Aeros.

There are two methods of determining the octane rating of a fuel, resulting in two different octane numbers for the same fuel, namely the Research Octane Number and the Motor Octane Number.

The test engine used to determine the Motor Octane Number is run at higher speeds and temperatures than in the Research Octane test, so a given fuel has a MON that is lower than its RON.
From memory, 95 RON fuel is about 85 MON.

The importance of this difference is that the fuel octane numbers quoted on fuel pumps in the US of A are an average of the RON and MON figures. I.e., the Eurosuper 95 RON fuel would be 90 octane in the US.

And for years I thought they just used bad fuel.....
 

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Quick question for Optimax users......

My 2.0L Carlsson is currently doing about 100 miles on £20 worth of Optimax, the computer tells me that I'm averaging about 20 to the gallon. Most of my driving is to work and back, a 7 mile trip each way starting on a cold engine.

I think my consumption is high but I'm not sure what to expect, what are the rest of you getting from Optimax?

Ps. I've been told to always run Optimax and only use unleaded if I have to, in which case I shouldn't take the engine over 3000rpm.

Cheers
 

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Originally posted by Dave Miller:
[qb]Quick question for Optimax users......

I think my consumption is high but I'm not sure what to expect, what are the rest of you getting from Optimax?

Ps. I've been told to always run Optimax and only use unleaded if I have to, in which case I shouldn't take the engine over 3000rpm.

Cheers [/qb][/b]
Not sure about your last point- that seems a bit excessive? THought the APC was supposed to govern performance in relation to the fuel used?


Anyway- with Aircon on - town driving - my 2.3 T does 22-24 gallon
Long journeys- sensible speeds- 28-30 mpg
Oh my god is that the time - type long journeys- 24-25mpg
Normal unleaded knocks these figures down by 5-10% so its worth the extra cost.
 

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The last point is something I was told by a Saab Garage who've been giving me advise here and there. I'm not sure how much creedance to pay to it either but I'll certainly stick to Optimax, especially if I'm going to get reduced mpg!!

Cheers

Dave
 

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I've used Silkolene Proboost, and have found a mild improvement in performance; on my first track day I had driven down with a tank full of Optimax and proboost. I refuelled part way through the day with Super unleaded and noticed a significant drop in performance- peak boost was down by 0.05 bar. It also felt a lot more sluggish.

I realise that's not totally valid as I'm amking the assumption that Optimax and the super unleaded are comparable. In more mundane driving though I can report a mild improvment in performance.

However, it does work out more expensive than Optimax so for regular driving I don't bother. I save it for the track...
(along with the 50/50 water/IPA mix in the washer bottle
)
 

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Anyway- with Aircon on - town driving - my 2.3 T does 22-24 gallon
Long journeys- sensible speeds- 28-30 mpg
Oh my god is that the time - type long journeys- 24-25mpg
Normal unleaded knocks these figures down by 5-10% so its worth the extra cost.  [/b]
My 2.3T Automatic (MY93) does 28-31 at 70mpg long runs on the motorway. Economy drops off like mad once you get into the dotted green on the rev meter (ie. above 65). My 2.0LPT (MY97) does 35-40 at 70. My brothers 2.3T Manual (MY92) does about 40mpg at 70mph. All of these figures are using standard unleaded from the local Jet Garage.

Steve
 

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Not all 2.3T manuals are geared the same (not sure about autos). Up to '92, the gearing was lower. This made for sprightly acceleration (as if they didn't all accelerate in a sprightly fashion
), but worse fuel economy. My '90 CD 2.3T returned an average of around 25mpg, while my '96 Aero, with the higher gearing, will give nearer 30mpg for the same type of driving. I can get 40mpg on a clear motorway run in the Aero, not exceeding 70mph, even with the power upgrades (which might actually help, rather than hinder fuel economy under these conditions).

Town driving in an auto will give appalling fuel economy, but on the motorway, my two CSE 2.0LPTs both return about 35mpg. One is manual and one is auto. Again, these are much lower-geared than a 2.3T.
 
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