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My father runs a 1999 Saab 9-3 2.0i light pressure turbo which averages about 35mpg rising to 46-47mpg on long motorway runs. Does anyone know if there would be any benefits in running the car on super unleaded? If so can these justify the extra cost? Also is it worth trying this in my 1994 single point injection 1.3 Mini Cooper? I realise the engine is basically a 40 year old design with modern fuel injection and because of this I am reluctant to try it; however I would still be interested to know. Any feedback would be greatly appreciated.
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The higher octane of super unleaded will give about 3% better economy, but only on cars fitted with knock control which can adjust to the higher octane. This economy improvement is therefore worth about 2p / litre so the cost way exceeds the benefit. Shell Optimax is said by some people to cause problems, even engine failure but others think it's great. I personally stick to supermarket unleaded with a dose of Redex Injection Cleaner every 1,000 miles.
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Ian,
my current vehicle (non-turbo V8) runs OK on supermarket fuel but there was a noticeable improvement when I switched to using regular Shell or Texaco unleaded. The engine idles smoother and the evidence, both seat of pants and gearshift patterns (it's and auto), indicate that there's more torque.
A couple of tank-fulls of Shell Optimax however, showed no improvement over regular unleaded. In fact the car developed an annoying and peculiar surge when running at constant part-open throttle. Switching back to regular cured it. I suspect that even though it has a knock sensor (and loads of others), the ECU just isn't setup to handle fuels like Optimax.
Turbo equipped vehicles are probably capable of accepting a much wider range of fuels, But... I think that your father will only find out if it's worth the extra cost of super unleaded by using it for a while and seeing if it makes any difference to his mpg figures.
In a '94 Cooper I don't think you'd see any improvement.
Kevin...
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