On DP There was a question posed as to what octane petrol did you put in your tank?
And the answer was 87.Seems very low to me
Going from Memory the UK octane numbers go:
2 star(regular)Unleaded 90-91
3 star(Premium)92-93
4 star(Super)94 (getting harder to find)
5 star 95-96? (obsolete)(also called Super)
Highest octane fuel unleaded is 95 octane but Older cars (large engines) Cannot run on this without modifications this was introduced only a few years ago. I think Vehicle with Cat. converters fitted all have to run on a higher grade than the "non cat convertor" Fitted models ?
More profit in fuel tax for the Government?

I have 3 questions:
What are the current US equivalent numbers?
And what octane rating was Pool Petrol During the war years?
What octane numbers is Diesel rated at?

Most US cars are designed for 87. Any higher in most US cars is just a waste of money. US gas ratings are usually 87, 89, and 92-93

The discrepency is in part due to the way octanes are reported. In the US, we take the average of the research octane number and the motor octane number and in the UK you take just the research octane number (which is always higher)

Did some checking.

This site says the RON is usually about 10 higher than the MON, making our octane ratings about 5 lower than yours. If that's right, our fuel be about 92, 94, & 97-98 on the British scale.

Diesel is not normally rated on the octane scale, but this site says it would have a rating of around 15-25 if it were.

Pool petrol appears to have been 80 (research octane number).

Thanks Methos for that
I saw this quote within the article:

quote:

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It might seem odd that fuels with higher octane ratings burn less easily, yet are popularly thought of as more powerful. Using a fuel with a higher octane allows an engine to be run at a higher compression ratio without having problems with knock. Compression is directly related to power, so engines that require higher octane usually deliver more power. Some high-performance engines are designed to operate with a compression ratio associated with high octane numbers, and thus demand high-octane petrol. It should be noted that the power output of an engine also depends on the energy content of its fuel, which bears no simple relationship to the octane rating.

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UK engines average about 12 to 1 compression these days to run on this fuel
Pre 1980's the top compression ratio was about 8 to 1 .Pre WW2 was circa 6 to 1.

Aviation Fuel, that was always the highest octane rating? circa 100 - 108?
I found some info here also on Road vehicle engines, but no octane range charts for it
www.mustangandfords.com/techarticles/30643/
I'll bet it is very expensive

The last time I bought racing fuel (110 octane) it was $4.00/gal. That was a few years ago however, and I'm sure it's more by now, but probably not more than $5.00 - $5.50.

A high compression engine here would be around 10.5:1. Those are the ones which require the 92-93 octane. My Focus SVT runs at 10:1 and requires a minimum of 91. Not using a high enough octane rating can seriously damage the car's engine and drastically shorten its life.

Another note: Since higher octane fuels are less volatile, the flame front in the combustion chamber spreads more slowly and evenly. This results in more complete combustion and fewer engine deposits. Any performance increase is negligible and there isn't any significant increase in fuel mileage, but higher octane fuels can keep an engine cleaner, therefore lasting longer. Whether or not the additional cost is a waste is arguable. But I can tell you that I use only the premium grade and I have never put less than 130,000 miles on any of my vehicles over the last 40 years. For me, it's worth it.

TC - I'm not a car expert, but I'm not sure about your last points. According to everything I've ever read, high octane fuel in a lower compression engine results in less complete burning and more unburnt fuel going out the exhaust and doesn't result in cleaner engines.

On a historical note, Exxon implied both claims in commercials in the mid-90s and the FTC ruled that this was unture advertising because they couldn't back up either claim.

Purely anecdotal Methos. At some point or another, I have torn down the engines on most of the vehicles I have owned. Without exception they show fewer deposits on valves, piston crowns and intake manifolds. I got the flame propagation information from Dennis Simanaitis, SAE and engineering editor of Road & Track magazine.