Home arrow Technical Articles arrow Hot Air 03/08/2003 (Silencer Systems)
Hot Air 03/08/2003 (Silencer Systems) PDF Print E-mail

We have spoken a good deal about branch manifolds over the last few months and delved into the intricacies that govern the effectiveness or lack thereof of header pipes, secondary pipes, different formats of branches and the differing design purposes of branch manifolds. Yet, we have only covered the surface of a very vast subject, which we will expand on as time progresses.

There are two main methods of developing branch manifolds for the road car:

The first method is the development of a branch manifold, which will enhance power when coupled to the existing stock exhaust system (silencer system). This is done a lot overseas where catalytic converters (cats) are mandatory. The R & D required is extensive because, as most of us are aware, a lot of the latest model cars come equipped with well designed manifolds, down pipes and silencer systems. One of the latest overseas trends is to install highly polished stainless branches on to the existing exhaust, which is kept stock up to the cat and a cat-back performance silencer system thereafter incorporating fancy ‘Jap-style’ rear silencer sections.


I have had the privilege of encountering a few such systems and on closer inspection have come to the conclusion that these systems have limited performance applications, which makes one think that these conversions are mainly cosmetic. Constructed of polished grade 304 stainless steel, although very aesthetically pleasing, not many of us in the good old RSA can afford the extremely high cost of such systems.


The young (and young at heart) South African motorist is a performance junky, full of enthusiasm for all things trick and racy, so development of bolt-on branch manifolds (to stock exhausts) isn’t even a consideration due to the inherent power gain limitations! In S.A. the enthusiast wants maximum power and torque. Looks and sound, also play an important role (for example: the popular installation of polished cold air induction piping and air filter, for the resulting characteristic induction noise and amazing polished stainless tail pipes for looks), which brings us to the second method of branch development.


The stock manifold and down pipes, especially on the latest model cars have been painstakingly designed and developed by the factory to:

  1. Minimize noise to conform with first world noise abatement regulations

  2. Route spent combustion gases along the length of the vehicle to exhaust into the atmosphere away from the driver and passengers.

  3. Reduce vibration and resonance levels to specified standards.

  4. Meet mandatory exhaust emission standards.

In other words, the stock manifold and exhaust system were designed together to develop maximum power and torque according to engine design spec and to cater for the above requirements!


If we uncompromisingly open up the exhaust system by means of larger diameter tubing and less restrictive silencing, we have ourselves a lot more potential for exhaust manifold development, because the stock exhaust manifold was designed for the stock exhaust system.


It stands to reason, therefore, that the free-flow silencer system should be developed separately first, to meet maximum power gains with sporty but acceptable noise levels as measured outside and, more importantly, within the vehicle.


In South Africa a lot of existing branch manifolds have been developed on dynamometers together with free-flow systems. By this I mean the branch manifold has not been developed separately from the free-flow system, nor has the free-flow system been developed separately from the branch manifold. These are essential steps to obtain the accumulative power gains of two separate modifications, otherwise we cannot be assured of the effectiveness of both items!


In the development of a free-flow silencer system, the natural tendency is to utilize larger diameter tubing and silencer bore in gradual increments until power gains level off. This can sometimes be a mistake. In the case of the VR6, for example, mentioned in issue 19,we reduced the exhaust pipe diameter from 63,5mm to 57,15mm to achieve the best results.



In the next issue:

What is the best exhaust diameter?

What is the best silencer box?


That’s all for now!

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