U.S.A. Series 1 1/2

[k.b.kennedy]

does usa series 1.5 engine compression ratios differ from uk spec

[Heuer]

Probably. US spec car's had an 8:1 compression ratio, UK had 9:1 to reflect the different quality of fuels available.

[Mark Gordon]

I believe it's the other way around. USA spec cars have the 9:1 compression ratio.
Mark

[Heuer]

The compression ratio will be on the engine number e.g. RXXXXX/9 or /8 - you could specify either although 9:1 was standard in the UK.

Mark - the European spec E-Type had the 9:1 compression ratio due to the wide availability at the time of 5 Star leaded petrol of 100 octane. In the USA the fuel quality was generally very low - 88 to 92 octane - the equivalent of our 3 Star petrol. This still holds true today so the lower compression ratio remains a better option for an XK engine used in the US:

"Generally, octane ratings are higher in Europe than they are in North America and most other parts of the world. This is especially true when comparing the lowest available octane level in each country. In many parts of Europe, 95 RON (90-91 AKI) is the minimum available standard, with 97/98 RON being higher specification (being called Super Unleaded). The higher rating seen in Europe is an artifact of a different underlying measuring procedure. In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in Canada, the United States and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in Canada and the US, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90?91 US AKI=(R+M)/2, and deliver 98, 99 or 100 (RON) (93-94 AKI) labeled as Super Unleaded - thus regular petrol sold in much of Europe corresponds to premium sold in the United States."

In Europe it is generally advisable to use super-unleaded fuel (Shell V-Power or BP Ultimate) to avoid pinking with a 9:1 compression ratio. Extract from the Service Manual:



Obviously performance was lower on the /8 engines.