Some information I have located regarding petrol.

** Please note that this information has not been verified, and has been collected from various sources **

        Octane rating

The rating of a gasolines performance in a test engine when 2,2,4-trimethyl-pentane is rated at 100.  RON is research octane number

Knock. - Preignition of the fuel mixture in the cylinder of a car engine, followed by spark ignition.

The sound produced is called “knocking” or “pinking”


The old “standard” petrol had an octane rating of 89.

The old “standard” petrol did contain a small amount of lead.

  The old “super” petrol had an octane rating of 97 (another article says 96).


      Valve wear preventative

         Leaded petrol

Tetraethyl lead works as a buffer against microwelds forming between the hot exhaust valves and their seats. Once these valves reopen, the microwelds pull apart and leave the valves with a rough surface that would abrade the seats, leading to valve recession. When lead began to be phased out of motor fuel, the automotive industry began specifying hardened valve seats and upgraded exhaust valve materials to prevent valve recession without lead

Tetraethyllead   (commonly styled tetraethyl lead), abbreviated TEL, is an organolead compound with the formula (CH3CH2)4Pb.

It was mixed with gasoline (petrol) beginning in the 1920s as a patented octane booster that allowed engine compression to be raised substantially, which in turn increased vehicle performance or fuel economy. Ethanol was already known as a widely available, inexpensive, low toxicity octane booster, but TEL was promoted because it was uniquely profitable to the patent holders. TEL was phased out starting in the U.S. in the mid-1970s because of its cumulative neurotoxicity, possible lung cancer contributor and its damaging effect on catalytic converters. When present in fuel, TEL is also the main cause of spark plug fouling. TEL is still used as an additive in some grades of aviation gasoline, and in some developing countries

 The publication SAE-Australia, September-October 1993 states:

... One advantage of leaded fuel was that the lead helped to reduce exhaust valve-seat wear, especially in cast-iron headed engines not fitted with alloyed valve-seat inserts, but with valves running directly into the head. The use of unleaded fuel (or gas) in these engines is likely to cause rapid valve-seat recession and eventually burnt valves. It further states: ... However, material used for valve-seat inserts for leaded fuels were not as good as the later insert materials, which are more resilient to wear. Such materials were developed specifically for unleaded fuel

         Un-leaded petrol

Methylcyclopentadienyl manganese tricarbonyl (MMT or MCMT) is an organomanganese compound with the formula (CH3C5H4)Mn(CO)3. Marketed as a supplement to the gasoline additive tetraethyllead to increase a fuel's octane rating, MMT was later used in unleaded gasoline


It is recommended to use a valve-saver fluid when using unleaded petrol in motors without hardened valve seats. 


1985 Unleaded petrol went on sale in Adelaide