Poor Grade Petrol Responsible For Cuts In New Cars’ Power

Gisborne Herald, Volume LXXV, Issue 22816, 10 December 1948, Page 7

Poor Grade Petrol Responsible For Cuts In New Cars’ Power

New cars’ failure to perform as well as pre-war models—a source of bitter complaints by their owners —is attributed by oil men and service stations largely to the low octane rating of petrol, which is Government-fixed. Except for aviation, no oil company is permitted to increase the octane rating beyond 72, compared with between 73 and 80 for super-grade petrol before the war.

Older cars are not greatly affected by the present quality of petrol, but the post-war engines, with their higher compression, tend to carbonise more readily and require more frequent tuning and adjustment.

Some of the effects of low-octane petrol are lower mileage, less pulling power, slower combustion, burning valves, and slower starting. Improved octane rating would mean controlled combustion with an evenflamed front in the combustion chamber, giving a powerful, even thrust to the cylinder instead of diffused combustion and jerky movements of the pistons. Determined by Tests. Octane rating is determined by tests. The octane number represents the relative proportion of two chemicals — iso-octane and normal heptane—needed to give the same knock characteristic in the testing engine. Iso-octane has an anti-knock rating of 100, while heptane, assigned. 0, knocks easily. By blending the two, various anti-knock values are reached. In the United States best-grade petrol has an octane rating of 78. while the average grade used has 7-45. It is authoritatively stated that if New Zealand rating were stepped up by even 2.5 it would make a big difference lo the performance of new cars. Ample quantities of tetro-ethyl lead or benzol, which are added to' petrol by the oil companies to obtain octane rating, are understood to be in storage in the Dominion and the companies would readily improve ihe anti-knock quality if they were permitted to do so. Before the war ethyl plants in New Zealand built up the octane rating from 72, at which it was imported. At a recent council meeting the North Island Motor Union supported a remit of the South Island Union that petrol rationing should be abolished and that the octane rating should be improved.