When the engine knocks ...
04/14/2015
In the past, advertising still contained really useful information. Here is an example from BP from 1965:
"In the engines of many cars there is a knocking, ringing or hammering sound. Because the compressed gasoline-air mixture explodes instead of burning. To be more precise: because the gasoline-air mixture ignites itself before it has been fully captured by the spark from the spark plug.
Each of these explosive self-ignitions increases engine wear. It also reduces driving performance because it interferes with smooth, rapid engine running. This is easily noticeable when accelerating quickly (for example when overtaking), on hills, at full throttle or when driving slowly in top gear: the engine no longer wants to start up properly, and the more it knocks, the less it does so.
Even more damaging for the bog and difficult to hear due to the stronger driving noise) is the so-called high-speed knocking on the highway or on long straights.
However, the engine only knocks if the octane rating (the degree of knock resistance) of the gasoline is too low. Gasoline with a sufficiently high octane value cannot ignite itself. It burns normally, through the ignition spark, and the full energy gained from the burnt gasoline-air mixture is transferred to the drive shaft without any disruptive explosion shocks. With octane-correct gasoline, the engine runs "smoothly", it pulls.
But what does that mean, sufficient knock-resistant or octane-grade gasoline? You can find it under the brand name Super made to measure at any BP filling station. Made-to-measure Super ranges from regular petrol (91 octane) through the three intermediate grades 93, 95 and 97 octane to pure Super (99 octane) and is graded according to price. The BP service station attendant will tell you the recommended upper and lower octane limits for the model and year of your car.
Within this range, you can choose the octane rating that suits your personal driving style. So the next time you need to fill up, drive straight to the Super to Measure pump - it's clearly marked at every BP filling station."
Of course, BP wanted to sell gasoline and preferably the more expensive one at that. But at least they explained the purpose of the high-octane gasoline in understandable terms. Which was perhaps necessary with five different octane options at the pump.
Incidentally, the advertisement can be found in Automobil Revue number 18 from 1965 on page 6.
