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Downton are perhaps the most prestigious company when one thinks of engine tuning on the 1100. On Downton cars the work that was carried out on the cars was simple, but after years of working on BMC A Series engines they'll know what they need to do in order to get better performance from the power unit. Downton never touched anything below the head. No balancing or lightening is carried out, the stroke and bore remain the same, and the camshaft and valves are standard.

This particular conversion was firstly carried out on an Austin 1100 Countryman.

So how did they do it? Well the secret of this conversion lays in the combustion chambers and inlet manifold design. Both of which were designed to give smooth delivery of mixture and even burning. In order to give the car an even better performance, the cylinder head was skimmed to raise the compression ratio from 8.5 to 9.1 :1, this is the maximum that a manual transmission car will take using regular fuel. On the inlet side the cast iron manifold was taken off and replaced with the buffer-type unit, with a single Su HS4 carburettor. The car's ordinary manifold is also scrapped and replace with the two branch one as fitted to Mini Coopers.

The automatic air cleaner and HS4 carburettor can be seen clearly in this picture.

Downton also would carry the conversion on the automatic transmission model, which was cheaper as a HS4 carburettor was already fitted. However compression ratios are slightly higher at 9.6:1. This is due to the torque converter stopping the engine from "slogging" at low speeds. Downton had also fitted an electric carburettor heater, designed to stop the carburettor from icing up.

A centre console is fitted with Rev Counter, oil and water gauges.


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