Exhausts for motorcycle rally raid competition

Monday, August 18, 2014

Tags :  exhausts

Many of us are probably familiar with the fact that for many years there has been an event called the Paris-Dakar rally. It is often highlighted by the fact that it has been well supported by motor manufacturers as well as star drivers in the cars and buggies – famous names from rallying such as Ari Vatanen, Juha Kankunnen and Carlos Sainz, as well as circuit-racing specialists such as Henri Pescarolo, Jacky Ickx and Jean-Louis Schlesser. During the winter, when motorsport on TV is normally confined to reviews of the preceding season, the Dakar rally provides some exciting variety.

Attracting less attention than the car category but no less competitive is the motorcycle category. The motorcycles have evolved over the years in a number of ways. In the early days, the key criteria for a motorcycle to be successful were reliability, plenty of ground clearance and a big fuel tank. The requirements for ground clearance and a large-capacity fuel tank made the motorcycles quite ponderous initially, and they remained vulnerable to mechanical damage in the event of any accident. As competition grew, speeds increased and it became more important to make the motorcycles tolerant of any day-to-day damage caused during riding as well as minor accidents.

The BMW R80 was often the machine of choice for Dakar rally entrants, the flat-twin engine offering the necessary ground clearance and the basic motorcycle being renowned for reliability. The exhausts on the early motorcycles were particularly vulnerable to damage, with the unprotected primary pipes exiting forward from the cylinder heads and being swept underneath the head before exiting in a low-level silencer. Later variants swept the exhaust upwards, with a high-level silencer being less vulnerable in the case of the rider falling off and when crossing rivers.

Over the years, more manufacturers were drawn to the Dakar, and the basic engine configuration of single- and twin-cylinder engines with front-exiting exhausts meant the first part of the primary pipes were less prone to damage from a collision, but perhaps more likely to being damaged by stones thrown up by the front wheel. Following the example of the later BMW R80 machines, rally raid bikes now all have high-level silencers, although they are sometimes only upswept just before the silencer entry. Having the silencer exit at a high level at least protects the engine from the ingress of water via the exhaust if the machine were to come to a halt in the middle of a river crossing.

What has happened is that the primary pipes are now very carefully shielded from impact damage and are very often not visible for most of their length, particularly where they are routed low along the side of the bike. Metallic as well as carbon composite materials have been used to protect the exhaust system from stone impact damage and from the results of the rider falling off the machine.

In recent years, the trend for motorcycles has been towards smaller-capacity machines that are more agile and easier for the rider to handle. From 2014, only single- and twin-cylinder machines with a maximum capacity of 450 cc are eligible, with the result that the manufacturers who produce 450 cc motocross and enduro bikes have had a sound basis for their rally raid machines. The entry from Yamaha, for example, is a single-cylinder machine, although this has a forward-facing inlet and a rear-facing exhaust. In this case, the primary pipe is much better protected from damage than some rival machines owing to the fact that the rest of the engine acts as a combined stone and bash guard for the pipe.

The exhausts are better supported than on many road and competition bikes too, with extra supports between the cylinder head and the silencer bracket.

Written by Wayne Ward

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