Fuel Consumption With Unleaded Fuel

The Graph

This graph show the fuel consumption averages for my Triumph Spitfire after it was converted to tun on unleaded petrol.

Graph of Triumph Spitfire consumption of unleaded petrol

Graph of Triumph Spitfire consumption of unleaded petrol

Follow this link to see the values that generated this graph.

Explanation of the Figures

The consumption figures are in miles per litre (mpl) as this is the easiest values to record in the UK now fuel is sold in litres. But for those who prefer miles per gallon (mpg) figures, a UK gallon is approx 4.5 litres. So:

9 mpl = 40.5 mpg
8 mpl = 36 mpg
7 mpl = 31.5 mpg
6 mpl = 27 mpg

Car Usage During This Period

During this time I was living mainly in West London so there was some more city driving although I really only used the car for longer journeys. After March 2001 the car was kept in Surrey with almost no town/city driving.

You can see from the frequency of the fill-ups that the car doesn’t get as much use during the winter months and there is presumably some evaporation of fuel from the tank which brings down the figures. Extra use of the choke would also bring down the winter average.

The raw average for the whole of this period was 8.13 miles per litre (approx 36.6 mpg). This is a small improvement on the figures from the period when the car was running on leaded 4-star (7.48 miles per litre).

Significant events during this period:

  • 9 July 1999 – Full service + carbs cleaned out.
  • 17 October 1999 – Multispark fitted. (see Note 1 below)
  • 8 February 2000 – Kenlowe fan fitted. (see Note 2 below)
  • 17 April 2000 – Service + leaky exhaust manifold fitted.
  • 9 February 2001 – Full service.
  • 14 October 2001 – Service.

Note 1

The Multispark is a unit placed in line with the lead to the distributor cap which delivers many sparks instead of one big one to each of the cylinders. Although as you can see there seems to be little or no impact on the fuel consumption, the engine was immediately a lot smoother and appeared to have more power so I perservered with it.

The pre-Multispark average consumption was 7.86 miles per litre and the average after was 8.25 miles per litre.

Note 2

The Kenlowe fan is an electric fan which replaces the previous mechanically driven fan. I was not expecting there to be much effect on fuel consumption, but there seems to be a small boost to the rolling average shortly afterwards.

I’d always recommend fitting a Kenlowe fan as the car was a lot quieter afterwards. Also there were no more tense moments sitting in heavy traffic on a hot day watching the temperature gauge rise. You can see a picture of the Kenlowe fan at the bottom of the Car History page.


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