Da do Ron Ron....

[chris.richard]

Should I be running my Alfa engine on the superunleaded rather than the lower octane normal stuff?

[Stratos]

I use Shell Optimax, but the engine was mapped to use that, and I never run anything else.

If you are going to be using it as a road car, it may not be feasible to have it set up specifically that way.

[Swamprat33]

Chris, I have yet to notice ANY difference between them tbh - apart from the price :eek:

Cheers

Tim

[rutthenut]

I hadn't bothered with the extra cost in general, on the basis that the stock ecu is not mapped to take advantage of the higher octane.

But one comment from Martin Kift makes me think otherwise - it's not that the ecu will increase ignition to make best use of high octane, but the better fuel should reduce the chance of the knock sensors detecting any pre-ignition, which would result in retarded ignition. Or something like that.

In other words, you won't get more power with the high octane fuel, but you are more likely to get what is available from the engine without premature 'self-preservation' leading to reduced power levels if any knocking is detected.

Still wouldn't bother for road use though, but will now fill up with that for competitive outings.

And a recent article highlighted the fact that super-spec fuel can be bought at Tesco's and the like cheaper than standard-spec fuel at most petrol stations!

[Martin K]

Just to remind people what we found on the Sanspeed rollers on my '91 24 valve Cloverleaf engined 164.

Graham at Sanspeed was tryning to tempt me to have a Superchip. Superchip hope to give an increase in torque by playing with the advance curve. We did power runs both before and after the chip was fitted but saw no gain at all. Then Superchips emailed another map - and still no improvement. A final map was sent that was retarded over the standard map - and we found some power improvement at last. This was all done on 95 octane fuel. After filling up with Tesco 99 we found even more power - so the map was obviously able to give the advance when called for. The final figure was 249 bhp on an otherwise standard engine with about 115000 miles on it - 10 bhp more than we could get with 95 RON.

I would therefore expect the standard ECU to give more power on higher octane fuel as it had more advance in it's map than my modified one - but we didn't do a dyno run to test the theory.

Martin

[Arthur]

I have standard Motronic on a standard 12-valve.
It's purely subjective, so having just forked out a fortune for high octane may be a contributory factor, but - mine will run quite happily on cooking unleaded, super, Optimax and BP Ultimate.
There is no discernibale difference between cooking and super, but it does like Optimax and Ultimate. Definite "crisper" feel to the engine, and its noticeably sharper on the throttle.
On mileage, it does around 31/32 mpg on cooking, 32 on super, but something like 33 to 35 on both Optimax and Ultimate, based on a couple of hundred motorway miles each time, driving at real world outside lane speeds, usual queues, and traffic either end.
On pure economics, I'd have to drive it very carefully (pah) to see a cost advantage in the "good stuff", but there's no real disadvantage either, so I spends the money, and enjoys the drive.

Only way is to give it a try - I have no idea what the chemists do the the stuff, but it seems to work, despite the apparent anomalies when calculated on a mass against fuel/air ratio basis.
I do know a number of bikers who say they can't even start a Blade on Optimax.........others who can't tell the difference.

[Martin K]

With Tesco, the answer lies in the Ethanol - or so they say!

An improvement to 33.6 mpg from 32 mpg is 5%. That is similar to the improvement in power that was achieved with my engine. It would seem likely that the 5% increase in torque would result in less throttle being needed to cruise and therefore a 5% saving in fuel.