Quote:
Originally Posted by Grant Bowker
I think Octane remains more likely. If 70 octane rating was "regular", with lower numbers being still available it would be reasonable if the Jeep required a minimum of 68 to specify the minimum to avoid someone using lower values. Surely the point of marking the tin is to ensure the correct product ends up in the correct vehicle but I've never heard of specific gravity of fuel or oil varying much (except with temperature - jet aircraft plan their required fuel load for a flight by weight since the energy content varies more accurately by weight than volume, then convert to volume, depending on temperature, for ease of measuring when pumping into the aircraft).
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Hansard, 13th November 1950:
Mr Russell asked the Minister for Fuel and Power if he will consider raising the standard of pool petrol to approximately 80 octane.
(Answer: basically not without substantially increasing its lead content, which might cause maintenance issues with British engines.)
Further down:
Mr Noel-Baker "Before the war we had three grades of petrol - commercial 68 octane, No.1 grade 75 octane and top grade 80 octane. I am advised that very few vehicles used 80 octane. Nearly all of them used the other grades. To raise our petrol to even 75 octane would mean a loss of output."
Much later...
The 1967 British Standard "Star" system had:
1 Star - 89 octane "Standard" or "Regular" (89 - 91)
2 Star - 92 octane
3 Star - 95 octane "Mixture" (by mixing Premium and Regular)
4 Star - 98 octane "Premium" (96 - 98)
5 Star - 101 octane "Super" (99 - 101)
Chris.