A Guide to Petrol & Variants
If your car has a knock sensor (as far as I know, all Calibras except for the 8V model), then you can get a noticeable increase in performance by using Super Plus unleaded petrol instead of regular Premium unleaded. The sad thing about this is that (as far as I know) Super Plus unleaded may be phased out but why not enjoy it while it's here?
If you own an 8v Calibra, you may be interested to know that my previous Cavalier SRi 8V (130bhp) didn't have a knock sensor but it DID have a strange type of 'plug' object right in the rear of the engine compartment on the left hand side of the car (left hand side if you're sitting in the car, right hand side if you're looking into the bonnet). This could be swapped for one that had "98" written on it. This would alter the ignition timing to make the most of 98 octane fuel. It's not as efficient as a knock sensor but it does give an improvement. I can't comment on how much difference it made because my Cavalier had it when I bought the car.
Back to knock sensors ... Because Super Plus has a higher octane rating (98) than Premium unleaded (95), it is less prone to pinking/detonation/knocking. The knock sensor detects this pinking and retards the ignition timing slightly. The management system keeps trying to advance it again until the knock sensor tells it to stoppit, etc. Consequently, the engine is always running with the timing as advanced as possible for the conditions.
This gives you the best efficiency and therefore the most power and best economy. Because Super Plus is less prone to detonation, if you run your car on it the timing will be running more advanced than it would if you were running Premium unleaded. Therefore, your car will give better performance and economy on Super Plus.
Super Plus is more expensive in the forecourt but this price difference is largely offset by the increased mpg you will get. In my own car, on Premium unleaded I usually get about 350 - 370 miles per tankful. On Super Plus it is often over 400. Typically, it's about 10% better. Once I'd been running Super Plus for a while (5 tankfuls), the car felt sluggish on Premium unleaded. Needless to say, I've always used Super Plus since! Remember when unleaded petrol was first introduced in this country? At the time, most cars were running on 4-star. 4-star is 98 octane - the same octane rating as Super Plus.
A lot of cars that could run on unleaded needed to have their timing retarded by a few degrees in order to use it. People noticed a drop in engine performance. You can get hold of octane boosters - a device that typically sits in your fuel line adding molecular tin to the fuel (some types are installed into the fuel tank). Tin is supposed to be an anti-detonant and therefore increases the effective octane rating of the fuel. I am currently testing one of these in my own car but I have not correlated any results yet. The claim is that it boosts the octane of Premium unleaded from 95 octane to 98 octane. If the claims are true, it should offer the same benefits as running on Super Plus but without the extra fuel cost.
Find out more later this year as we evaluate the use of such a device.
