15/6 Specifications

as Old as the Industry, as modern as the Hour
Featuring: Brief History; Engine Development; Recognition Features.

Brief History

The 15/6 engine was little more than a bored-out 14/6, thus providing more power and higher performance figures. This block saw many different bores and strokes, as Riley used it for their Racing Cars, thus needing it to fit several racing categories.
The 15/6 was the replacement for the old 14/6 in the Riley range, and was introduced in 1935, with the standard range of bodies and the Stelvio from the 14/6 range. The bigger engine gave more power and refinement for a more modern car.

The 15/6 remained in limited production until the recievers arrived in early 1938, although it is thought that some surplus blocks were put in cars much later. However, it was effectively replaced by the new 16/4 in 1937, and had been overshadowed by the 8/90 before that. Even so it sold steadily, and was available with a wide range of bodies.

Engine Development

In true Riley style, there were two 15/6 engines. The first was simply a bored out 14/6 hastily designed to update the ageing Stelvio and Winchester models, although it is doubtful if more than a handful of the latter were sold. The engine was also used for a handful of the MPH Sport cars.

The definitive 15/6 engine, however, was quite different. Whilst retaining the same basic building blocks as the old 14/6, the engine was a thoroughly revised and refined unit, incorporating all of the latest ideas in engine design, many of which were first implemented in the smaller 12/4 engine of the previous year. Whilst it is not entirely certain, it seems that some of the larger bore 2 litre 6 cylinder racing engines also owed their origins to the new 15/6 unit.

Recognition Features

There are, perhaps unfortunately, few outward signs to identify a 15/6 Riley from it's contemporaries. Perhaps this was Riley's attempt at understatement, or maybe a rare acknowledgement that costs needed to be kept under control. The chassis is a development of that used on the smaller engined 6 cylinder cars, and was itself further developed for the later V8 and Big 4 ranges. Similarly, the bodies were little different from those fitted to the other larger cars.
Most cars retained the traditional black radiator, but once the 16/4 was launched with the chrome-slat grille, it seems likely that some of the last 15/6 cars would have also had this fitted as a necessity.

Inside, the trim levels were higher than those of any other Riley model at the start, but clearly the arrival of the V8 in 1936 changed this, and it is likely that the trim of the 15/6 was reduced moderately to better distance the new flagship models.
Under the bonnet, even a casual observer could quickly identify a 6 cylinder rather than 4 cylinder engine, but sadly it is not so easy to differentiate between the 3 different sizes of 6 built.